'Dark fluid' with negative mass could dominate the universe - <AUTHOR> https://theconversation.com/bizarre-dark-fluid-with-negative-mass-could-dominate-the-universe-what-my-research-suggests-107922 <comment><USER2> Paper: [https://arxiv.org/pdf/1712.07962.pdf](https://arxiv.org/pdf/1712.07962.pdf)

Not a physicist, but my summary of the author's point would be:

If you allow for matter with a negative mass and plug it into a n-body simulation. You seem to get what looks like dark matter from first principles. Namely, a halo of non interacting matter around galaxies in just the right "non-cuspy" shape. Their conclusion is that this is worth considering, as almost all mainstream cosmology makes the assumption that mass >= 0, despite the fact mass <=0 doesn't seem to violate any physical invariants we know.

The idea is persuasively simple. Every other force besides gravity is polarised, so why not also gravity? It seems interesting to me, but I'm nowhere near knowledgeable enough to know whether it can be easily refuted.

<comment><USER3> Here's an argument:

If you think about it, "mass" actually means two different things. One one hand, there is mass as the "charge" of gravitational interaction, that is, the gravitational field generated by a body is proportional to its mass. Let's call this concept "gravitational mass". On the other hand, you have mass in the sense of "intertial mass", a body's resistance to change of velocity. Although we kinda take it for granted, it's weird that these two concepts coincide, and not something that would be necessarily true _a priori_.

Asserting this equivalence as a principle is the starting point for Einstein's theory of General Relativity, which is one of the most beautiful and thoroughly tested theories in modern physics.

On the other hand, you can show that the inertial mass cannot be negative (else the Lagrangian would not be bounded from below and therefore you could not minimise it; the whole of physics then comes crumbling down). Therefore, if that equivalence stands, the gravitational mass also cannot be negative.

<comment><USER4> > On the other hand, you can show that the inertial mass cannot be negative > (else the Lagrangian would not be bounded from below and therefore you could > not minimise it; the whole of physics then comes crumbling down).

Here's a purely thought-experiment argument for inertial mass not being negative:

If you had an object with negative inertial mass, then pushing on that object would cause it to accelerate into your hand. This is a positive feedback loop that immediately results in the object and your hand exerting infinite amounts of force on each other, because applying force just leads to applying more force.

<comment><USER5> Here's a thought experiment that shows that there can't be electrons:

"If you had an object with negative charge, then putting that object near a positive charge would cause it to accelerate towards the positive charge." Getting closer increases the force. "This is a positive feedback loop that immediately results in the object and the positive charge exerting infinite amounts of force on each other, because" getting closer "just leads to applying more force."

Thus, there are no electrons.

So, I don't think the thought experiment rules out negative mass. In fact, the article explicitly says "if a negative mass was pushed, it would accelerate towards you rather than away from you.", and I assume that if that's an obvious contradiction, the author would have caught it.

<comment><USER4> So, electrons are attracted to protons by the electromagnetic force, but they don't make it all the way there because they are repelled by some other force. You don't have a paradox because our model of the electromagnetic force doesn't specify that it's the only force there is.

But if a negative mass is moving towards you and encounters a repulsive force, that repulsive force will, by definition, move the negative mass further toward you. It would need to encounter an _attractive_ force to reach equilibrium.

Note that, unlike in the electron example, it doesn't matter what kind of force is being applied; the object's negative mass tells us that the response to any repulsive force is acceleration towards the force.

<comment><USER6> > they don't make it all the way there because they are repelled by some other > force

A repulsive force is not the best way to think about it. The potential of the nucleus is the usual -1/r, and goes to (negative) infinity at zero. A repulsive force would be incorporated into the potential and appear as a bump around the nucleus, and would mess up the electron orbital.

A hand-wavy explanation of why the electron doesn't fall in: if you try to push the electrons into the nucleus, you necessarily localize the electron into a smaller volume; this means its wavefunction must get "spikier" and therefore it has more kinetic energy. This kinetic energy rises faster than the potential energy drops, so the state of lowest energy is actually found at an average radius > 0.

Note that it took quantum mechanics to rescue the atom. A classical electron could fall into the nucleus.

I do not see any problem with a negative-mass particle accelerating towards the force. The analogy with opposite charges seems right to me.

<comment><USER7> A different hand-wavy explanation. The places that an electron can be found are described by a wave pattern. If the electron is staying in place around a nucleus, that wave pattern has to be a standing wave that reinforces itself. To reinforce itself it has to wrap around the nucleus an integer number of times.

This explanation doesn't just explain why it doesn't fall in, it also explains why there are discrete shells that it could be found in, corresponding to how many times it wraps around the nucleus. (It doesn't explain why only a finite number can fit in each shell though. Or why bigger shells can have more electron orbitals. Or...well the actual theory has to be good for something!)

<comment><USER4> I'm not really interested (here) in the reality of the interaction between the electron and the nucleus. I don't think the existence of an electromagnetic field is a good argument against its own existence as argued by FabHK further up.

I also don't think FabHK's argument works as an analogy to my problem with negative mass. The electromagnetic field is not self-reinforcing in the same way.

Imagine that you're holding a marble of negative glass in your fist. Negative glass is indistinguishable from ordinary glass except that its mass is negative rather than positive.

As we all know, the first step in solving any physics problem is to draw a free-body diagram. ( [http://www.smbc- comics.com/comics/20130616.png](http://www.smbc- comics.com/comics/20130616.png) ) Let's draw one here. First, we'll do one for an ordinary marble:

1\. The enormous mass of the earth attracts the marble downward proportionately to the marble's mass.

2\. The marble cannot accelerate downward, because it's stuck in your fist. Your fist experiences a downward force equal to the weight of the marble.

3\. By Newton's third law, your fist exerts an upward force on the marble equal to the force exerted by the marble on your fist. This is exactly equal to the weight of the marble, but in the opposite direction. The two forces cancel, and the marble is at rest.

Now for the negative marble:

1\. The enormous mass of the earth attracts the marble downward proportionately to the marble's mass. Because that mass is negative, the marble attempts to accelerate upward.

2\. The marble can't accelerate upward, because it's stuck in your fist. Your fist experiences an upward force equal to the weight of the marble.

3\. By Newton's third law, your fist exerts an downward force on the marble equal to the force exerted by the marble on your fist. This is exactly equal to the weight of the marble, and in the same direction, effectively doubling the marble's weight. The marble is now trying twice as hard to accelerate upward into your fist.

2\. (Again.) The marble can't accelerate upward, because it's stuck in your fist. Your fist experiences an upward force equal to double the weight of the marble. Nothing has moved; we're still just trying to work out the balance of forces within the system at rest.

3\. (Again.) You can see where this is going.

What is the conceptual breakthrough that rescues negative mass from this trap? (Note that saying the marble has negative inertial and gravitational mass, as opposed to negative inertial mass and positive gravitational mass, doesn't help: the marble will be trying to accelerate downward instead of upward, but it will still be doing it with infinite force.)

<comment><USER8> Maybe that's precisely why objects with negative mass do not exist on the Earth? But what stops them to exist in the void of space, between regular matter? And it doesn't need to be actual "objects", but isolated particles or a particle gas. In relativistic physics mass is dependent on the body's energy, so negative mass implies negative energy.

</comment></comment></comment></comment></comment></comment></comment></comment></comment><comment><USER9> Looks like the rest of the world is about to catch up with Jean-Pierre Petit's theories about negative masses surrounding positive mass objects like galaxies and holding them together... Even the proposal for the modification of Einstein's theories... Times are a'changin.

It took almost ten years (2007-2017) from JPP being shunned by the scientific community (and the highly politicised French Wikipedia) to others "discovering" the same things he had been saying all along. [https://arxiv.org/abs/0712.0067](https://arxiv.org/abs/0712.0067)

[http://jp-petit.org/papers/cosmo/2018-AstrophysSpaceSci.pdf](http://jp- petit.org/papers/cosmo/2018-AstrophysSpaceSci.pdf)

You may give yourselves the smallest pat on the back in the universes.

<comment><USER10> figure 1 of that paper is virtually identical to the galaxy rotation curve of the current paper! both were N body simulations

thanks for pointing out this earlier work

</comment></comment><comment><USER11> I found the author's Twitter summary of the paper useful as well: [https://twitter.com/Astro_Jamie/status/1070302359325151233](https://twitter.com/Astro_Jamie/status/1070302359325151233)

<comment><USER12> Threadified: [https://threadreaderapp.com/thread/1070302359325151233.html](https://threadreaderapp.com/thread/1070302359325151233.html)

</comment></comment><comment><USER5> I've personally verified this part of the paper:

> Observations clearly indicate that the Universe is not empty.

EDIT to add: Another nice, slightly Douglas-Adams-y quote:

> This implies that our Universe is just one of those things that happen on > occasion, and we can simply think of its existence as being illustrated by a > 1 billion-σ statistical event.

</comment><comment><USER13> >The gravity from the positive mass galaxy attracts negative masses from all directions, and as the negative mass fluid comes nearer to the galaxy it in turn exerts a stronger repulsive force onto the galaxy that allows it to spin at higher speeds without flying apart.

I don't get this, seems contradictory.

<comment><USER14> Maybe it was modeled as a curvature of space? So positive masses curve space so that everything moves toward them - including light, massless particles, and negative mass. And negative mass repels everything, including other negative mass, by shaping space differently.

[Edit: jbay808 has a better explanation below, and negative mass _attracts_ negative mass.]

That behavior is described here [https://en.wikipedia.org/wiki/Negative_mass#Runaway_motion](https://en.wikipedia.org/wiki/Negative_mass#Runaway_motion) but it's not what I was expecting either.

<comment><USER15> Yeah this helped me create a mental picture that kind of makes sense. It would clarify why negative mass is also concentrated in areas of high mass, and could also provide the mechanism for constant universe expansion, as the space between masses is constantly being pushed away by the diffuse negative mass. Heh, armchair physics is fun :)

</comment></comment></comment><comment><USER16> > Air bubbles in water can be modelled as having a negative mass.

Forgive the naive take on this, but it's a weird point to me... if air bubbles in water can be _modelled_ as having negative mass, but clearly do _not_ (they are made of particles with positive mass), then they are only "negative" in relation to the material surrounding them. So even if they can be modelled this way successfully, clearly the model doesn't imply for certain that they do have negative mass. So by analogy, just because a negative-mass model can explain the observations of dark matter, doesn't it still leave the question of whether anything "real" is implied by it? Perhaps it's just a reflection of a negative relative to some unknown bias (field), like the Higgs field, but in "absolute" terms is not actually negative.

(Not sure "absolute" has any meaning here..)

<comment><USER17> The concept of whether something is "real" is a metaphysical amusement. And it is never meant to be answered in modern physics. Physics has come a long way into what it is today from natural philosophy. I believe all physicists in this day and age subscribe to the notion of model-dependent realism in one way or another. [https://en.m.wikipedia.org/wiki/Model- dependent_realism](https://en.m.wikipedia.org/wiki/Model-dependent_realism)

Perhaps someday in the distant future we will discover that many assumptions in physics are simply wrong since we really do indeed live in a computer simulation and it is one where the Von Neumann architecture holds so it is always possible to alter "physics laws" like the Pauli exclusion principle and "physics constants" like the speed of light. And these "physics laws and constants" do get altered under certain if-statements or else there will be bugs and the simulation will crash, rebooting itself as a result.

Or perhaps this simulation does crash and reboot itself very often. It's like elixir. We simply are not aware of it. Maybe that could be why we have things like the Heisenberg uncertainty principle and quantum tunnelling.

<comment><USER18> Or not so distant future. There has been a relative standstill in physics in spite of perhaps more 'known unknowns' than ever before. The problem with models independent of 'reality' is a lack of falsifiability. This in turn means the model itself becomes indefinitely self sustaining even when it's completely wrong as each wrong prediction is then simply massaged back into the model to artificially produce a correct answer.

For instance a recent conversation I had was discussing the big bang and the cosmic microwave background radiation. Somebody thought that the CMB was evidence of the big bang. Of course when the CMB was first observed/measured it completely falsified our idea of a big bang due to the horizon problem -- regions of space that should not be causally connected are somehow homogeneous, which should be impossible. But instead of this observation != prediction indicating some fundamental problem we instead add in a magical hyper-inflation period to the model of the big bang so that the model can now "predict" what we see. And now you have people that believe that the CMB itself is evidence of the model's accuracy, when in reality the CMB refuted our models and we were forced to massage it back into the model in a rather arbitrary fashion. There is absolutely no physical reason to accept hyper- inflation other than 'if we add this magic event, then we can keep using this model.'

For a less contemporary example consider geocentricism - the idea that everything rotated around the Earth. Prior to Newtonian mechanics and other 'real' systems of interaction, we simply used models for orbital mechanics. And these models ended up being quite rediculous. You had planets doing magical swirlies, stopping and going backwards, and all other sorts of things. But because you can't falsify models detached from reality, everybody just shrugged their shoulders and accepted it for something on the order of centuries. And as time passes these models become even more difficult to replace because it ends up meaning you'd basically have to toss something on the order of decades, if not centuries, of past work. In this particular case astrology, for instance, was in the past a scholarly and academic field analogous in many ways to psychology today. Refuting geocentricism involved completely scrapping this entire field, and centuries of work within it, due to the fact it took things such as Mercury going backwards as key components of its analysis of human psychology.

The point of this all is that as you accept models, it can be that you're searching for answers at the entire wrong level of a problem. For instance astronomers in times of a geocentric universe may have been trying to explain why Mercury went backwards during its orbit, yet it's extremely difficult to answer something when you start with a wrong assumption -- in that case that the planet does indeed go backwards at some point, planets have these orbital swirlies, and so on. People like to rewrite history to blame geocentricism on the church, but inertia is not limited to divine belief.

</comment></comment></comment><comment><USER19> If anyone is interested in dark matter and dark energy I recommend this book: [https://www.amazon.com/Our-Mathematical-Universe-Ultimate- Re...](https://www.amazon.com/Our-Mathematical-Universe-Ultimate- Reality/dp/0307599809)

Written by this guy [http://web.mit.edu/physics/people/faculty/tegmark_max.html](http://web.mit.edu/physics/people/faculty/tegmark_max.html) is does a fantastic job of going from really simple concepts/experiments to blowing your mind.

</comment><comment><USER20> Would this be only gravitational mass that's negative or would it be both gravitational mass and inertial mass? Because negative inertial mass is zany and wierds me out. Negative gravitational mass behaves in a way that makes sense to me.

<comment><USER21> Has to be gravitational only. Otherwise positive mass is repelled from negative mass, but the negative mass accelerates towards it. So both masses accelerate in the same direction, until they have infinite kinetic energy!

Conservation of energy & momentum would still hold, because negative mass would have negative energy & momentum, cancelling out that of the positive mass.

But the above surely would be an 'unphysical' situation.

<comment><USER22> >Negative masses are a hypothetical form of matter that would have a type of negative gravity – repelling all other material around them. Unlike familiar positive mass matter, if a negative mass was pushed, it would accelerate towards you rather than away from you.

Pretty sure the author means both.

A continuously accelerating system seems "unphysical", but we have an example already: the accelerating expansion of the universe.

</comment></comment></comment><comment><USER23> I'm curious about the idea of "allow[ing] negative masses to not only exist, but to be created continuously." Given the law (in the scientific sense) that matter/energy cannot be created or destroyed, on a scale of 1 to FTL travel, how crazy is this idea?

<comment><AUTHOR> I thought it was less a law and more of an observation.

<comment><USER24> Scientific laws are just quantified observations.

</comment></comment></comment><comment><USER25> Sounds a lot like the concept of the Dirac sea to me.

[https://en.wikipedia.org/wiki/Dirac_sea](https://en.wikipedia.org/wiki/Dirac_sea)

Rather than have dark matter particles, have negative mass dark matter particles in every other location instead.

<comment><USER26> This is explicitly very different from that. There's no claim of "negative mass dark matter particles" in _ever_ location, rather, they have a specific distribution.

<comment><USER27> That distribution being all the places that aren't normal matter particles. So primarily outside of galaxies.

<comment><USER22> No. The negative mass matter clusters around galaxies because it accelerates towards positive mass and away from other negative mass. The area between galaxies becomes largely empty in the simulations.

</comment></comment></comment></comment><comment><USER28> I recall reading article in a popular science magazine about hypothetical negative mass with exactly these properties. It was about 25 years ago and the magazine was Russian language. Unfortunately, I can't recall its name now.

<comment><USER28> Oh, thanks to the power of the internet search, I found a scan of that article: [http://epizodsspace.airbase.ru/bibl/tm/1990/10/otrits- massa....](http://epizodsspace.airbase.ru/bibl/tm/1990/10/otrits-massa.html) The journal is "Техника-молодежи" (a Soviet style name that I am incapable of translating to English) and the article is from 1990.

And that article refers to a publication by Robert Forward in a journal with a name like Aerospace Technology or Aerospace Engineering. But I found an article in on the same topic in NewScientist: [https://www.newscientist.com/article/mg12517084-200-the- powe...](https://www.newscientist.com/article/mg12517084-200-the-power-of- negative-matter/)

Wikipedia, of course, has an article on Negative mass as well.

<comment><USER29> Thank you! The first thing I did when coming to this thread was search for posts containing "Robert Forward", as any discussion of negative inertial mass is incomplete without mentioning his work. So, kudos.

Anyone interested in the implications of negative mass should probably check out Timemaster, a sci-fi novel by Forward. Negative mass can hypothetically do some interesting things. Things such as allowing lightspeed travel by matching negative mass to positive mass in equal amounts, leaving a non-photon object with rest mass = 0, or producing energy by accelerating negative mass to high velocities.

Unfortunately, Forward is much better as an idea guy than he is as an author. The scene where the hero travels back in time and has a threesome with himself and his wife is a bit awkward...

</comment></comment></comment><comment><USER30> What's the relationship between negative mass and negative gravity and anti- gravity? Dark fluid is repulsive, so is it theoretically possible to collect a ball of it, put it between you and another positive mass, and fly apart?

<comment><USER31> Yes, that is essentially my understanding

</comment></comment><comment><USER32> Sounds a lot like phlogiston, especially since it apparently must be continuously created to matched observable behavior.

<comment><USER33>
      Beware the Physical Chem, my son!
      The laws that arn't, the constants that vary.
      Beware the phlogiston, my little one
      And of the molality be wary.

      He took his entropy in hand
      Long time the adiabatic foe he sought
      So rested he by the delta T
      And stood awhile in thought.

      And as in Newtonian Thought he stood
      The Physical Chem with Beer's Law Plot,
      Came Bohring through the orbital wood
      And took quantum leaps when hot!
      PV! RT! And with fugacity,
      The entropy discharged his wrath.
      It reached a degenerate state, and being late,
      He returned by the mean free path

I wonder if anyone will recognize this. :)

<comment><USER34> If by recognize you mean that it's a variation/remix of "Jabberwocky"[1], then yes.

The second corresponding verse (so this corresponds to "He took his entropy in hand"), so others can see the resemblance (I chose the second since the first is a bit harder to see):

      He took his vorpal sword in hand:
      Long time the manxome foe he sought—
      So rested he by the Tumtum tree,
      And stood awhile in thought.

[1]: [https://en.wikipedia.org/wiki/Jabberwocky](https://en.wikipedia.org/wiki/Jabberwocky)

<comment><USER33> Very cool. Today I learned something about a AXE (Alpha Chi Epsilon chemistry fraternity).

</comment></comment></comment></comment><comment><USER30> Here's an article describing the theory that sound waves have negative mass. It also describes it in terms of the behavior of fluids.

[https://www.realclearscience.com/articles/2018/08/11/could_p...](https://www.realclearscience.com/articles/2018/08/11/could_phonons_have_a_negative_mass_110719.html)

Maybe these phenomena are linked, and it's more immediate than cosmology.

via: [https://twitter.com/robinhanson](https://twitter.com/robinhanson)

</comment><comment><USER35> This then leads to the inevitable questions, is an Alcubierre Warp Drive possible, since one of its pre-requisites was particles of negative mass?:

[https://en.wikipedia.org/wiki/Alcubierre_drive](https://en.wikipedia.org/wiki/Alcubierre_drive)

>>a spacecraft could achieve apparent faster-than-light travel if a configurable energy-density field lower than that of vacuum (that is, negative mass) could be created

If this matter is popping into space continuously as the author describes, it could be possible to harvest it. The question is, how much of it is popping into existence in lets say a square km of space (something we could feasibly cover with our current tech), and how do we detect and capture it.

The author does readily admit that his theory may be wrong, but useful as a mathematical tool. It's like saying "My theory may be the Newtonian Mechanical model of dark matter + dark energy, but not the quantum (read: real) theory." I sure as hell hope he is correct and its a real particle we could capture. It could open up technology we have yet to realize and get us off this rock.

</comment><comment><USER36> Two passages from the article:

> Negative masses are a hypothetical form of matter that would have a type of > negative gravity – repelling all other material around them. Unlike familiar > positive mass matter, if a negative mass was pushed, it would accelerate > towards you rather than away from you.

> The gravity from the positive mass galaxy attracts negative masses from all > directions

...why aren't these contradictory?

intuitively... wouldn't a negative mass be _repelled_ by positive gravity?

(I am not a physicist of any kind, obviously)

In the author's Twitter thread [https://threadreaderapp.com/thread/1070302359325151233.html](https://threadreaderapp.com/thread/1070302359325151233.html)

there is this image: [https://pbs.twimg.com/media/Dtp7YjWW4AEIvSp.jpg](https://pbs.twimg.com/media/Dtp7YjWW4AEIvSp.jpg)

..which seems to answer my question

If I understood the picture:

\- positive mass gravities attract each other and result in acceleration towards each other

\- negative mass gravities attract each other, but the negative mass means this attractive force results in an opposite acceleration (they behave as if repelled)

\- a positive mass and a negative mass have gravities which repel each other so the positive mass accelerates away from the negative, but the negative mass inverts its gravitation repulsion into an acceleration _towards_ the positive (I find it hard to imagine how this interaction actually plays out, it's a bit counter-intuitive.. I guess they must cancel out rather than chasing each other faster and faster?)

</comment><comment><USER37> Interesting rebuttal from someone in the field (who is actually quoted in the paper): [http://backreaction.blogspot.com/2018/12/no-negative- masses-...](http://backreaction.blogspot.com/2018/12/no-negative-masses-have- not.html)

</comment><comment><USER38> One of the most interesting properties of matter with negative mass is that if something collides with it it accelerates in the opposite direction of the incoming object.

[https://en.m.wikipedia.org/wiki/Exotic_matter#Negative_mass](https://en.m.wikipedia.org/wiki/Exotic_matter#Negative_mass)

</comment><comment><USER39> Titles that describe poorly understood scientific phenomena as "bizarre", "mysterious" etc., hurts science, IMO. I would expect this from a journalist (though not excuse it), but an academic?

Why not something like "Negative mass dark 'fluid' halos around galaxies as an alternative to dark matter"?

</comment><comment><USER40> Stupid non-physicist question here: we know the universe is expanding, but where does it expand at? Are there physical areas which we can observe growing? And if so, shouldn't that mean that we observe distant objects as lighter than their interactions with closer objects would imply?

<comment><USER41> Space expands everywhere, also right in front of you, it is just a very small effect over short distances. Two points one meter apart expand away from each other with a speed of 0.07 nanometers per year. For short distances electromagnetic and strong forces just pull everything immediately back together as things want do move apart. Over larger distances, think the scale of galaxies, gravitational forces keep the stars, the gas, and all the other stuff together and prevent galaxies from expanding.

But once you move beyond the scale of galaxies and galaxy clusters there are no longer any forces strong enough to counter the expansion of all that space between galaxies and so in general the distances between galaxies are increasing. There are still exceptions, in clusters of nearby galaxies gravitational forces can still bind those galaxies together but with increasing distances between galaxies the expansion finally overpowers gravitational attraction.

It is important to remember that not only are all forces becoming weaker as distances increase but also that points are expanding faster away from each other as their distance increases. As said, two points one meter apart move away from each other with 0.07 nanometers per year but two points one kilometer apart move away with 70 nanometers per year because there are a thousand meters in between them, all of them simultaneously expanding at 0.07 nanometers per year.

<comment><USER42> > Space expands everywhere, also right in front of you, it is just a very > small effect over short distances ... .07 nanometers per year but two points > one kilometer apart move away with 70 nanometers per year because there are > a thousand meters in between them

No, what you wrote is contradicted by evidence from within the inner solar system (MESSENGER's observations of solar mass loss were highly sensitive; we have excellent VLBI too), from other star systems, especially eclipsing binaries and systems with occluding planetary systems) and from galactic dynamics (LSR tests, peculiar motions, and lots of DM/dynamics evidence for galaxies at different redshifts). It is not how the standard model of cosmology works either. Grossly, 0.07 nanometers per metre per year expansion everywhere would be impossible to hide from solid state physics, and even several everyday polymers and ceramics; an expansion term would have to appear in accurate descriptions.

We cannot say there is _no_ expansion at these scales, but the expansion is highly constrained and evidence requires that it effectively vanishes. A fifth-force mechanism like quintessence requires a shutdown mechanism inside galaxies that contain star systems like ours or TRAPPIST-1 or PSR~J0337+1715. Additionally it likely would need a shutdown in small structures (like asteroids) ejected from galaxy clusters by violent events, although we will not spot those in practice any time soon. Where there's a shutdown mechanism there's also a wake-up mechanism that has to be considered too, and high- redshift observations constrain the wakeup of quintessence action to relatively late times. What suppressed quintessence for a bit more than three billion years after the formation of the cosmic microwave background?

These type of modellers run into the hard problem that as they work out the parameters of their theory, they (so far) find they all are consistent with the standard cosmology. (That shouldn't be too surprising; LambdaCDM, the standard cosmology, was carefully built to concord with evidence "forward- compatibly".)

One way to put it is in the name: cosmic expansion, rather than universal expansion, distinguishing between effects apparent at the largest scales, and effects apparent everywhere in the universe, at all scales.

LambdaCDM is a model of an universe well-described by an expanding Robertson- Walker metric and matter in the large obeying the Friedmann equations. The expanding metric includes a term for the cosmological constant. The matter is essentially a space-filling fluid at rest, isotropic, homogeneous, and being diluted away by the expansion of the background Robertson-Walker spacetime. (It is in a special frame of reference in this model in which Dark Energy arises as a non-diluting homogeneous fluid imposing constant isotropic tension on the matter fluids. In general frames Dark Energy is just the cosmological constant.)

On the LambdaCDM model we can overlay the 'swiss cheese' model; this is standard too, but we are departing from cosmology and heading toward astrophysics. The motivation of 'swiss cheese' is simple: at the largest scales, the Friedmann Robertson-Walker model sketched above describes all observations between well and _extremely_ well. However, it does not describe gravitationally-bound systems like galaxy clusters, galaxies, or star systems. Those are much much better described with conventional clumping matter (and dark matter) inside a collapsing Tolman spacetime. Notably, none of these systems are homogeneous (they contain lumpy bits like planets and stars, and sparse bits like the interstellar medium) and all of them contain radiating orbiting material; that they are radiating implies gravitational collapse (there's also plenty of other evidence for that). The Friedmann-Lemaître- Robertson-Walker (FLRW) cosmological model does not describe these systems.

In 'swiss-cheese', the FLRW cosmological model is the cheese. If we treat the cosmological-scale matter fluid as a dust that is only homogeneous at the largest scales, the dust can be lumpier in some places and sparser in others. The lumpiest bits represent galaxy clusters that remain gravitationally bound over cosmological times. We then "swiss" this lumpy cheese procedurally: we cut out a region of the Friedmann matter on the Robertson-Walker background and replace it with a region of galaxy-cluster matter on a Tolman background, and stitch the two together using junction conditions on the boundary. (Typically we do this to the densest lumps, the galaxy clusters, but we could do the same procedure in deep intergalactic space instead. A spherical region of that will not be exactly void, since it will contain at least photons and neutrinos produced in the early universe, likely a bit of baryonic matter from big bang and supernova nuclear synthesis, and possibly a small amount of dark matter too: however all this stuff is so sparse that it would not generate a collapsing spacetime metric -- calculated out, it would resemble a slightly perturbed expanding Robertson-Walker metric. So we don't put "holes" there; our "holes" contain galaxies.).

In a swiss-cheese model there is simply _no_ expansion in the "holes", because the Tolman backgrounds that work do not contain a cosmological constant term. (The typical problem is that something that _does_ contain expansion, like a Kottler vacuole, evolves away from a mass-compensating comoving void, e.g., the hole grows much too fast or in strange ways that do not match any of the tens of millions of galaxy clusters in our sky).

Since Tolman/FRW swiss cheese models [a] are tractable in practice and [b] match observations extremely well, it is perfectly reasonable to take the hint that nature doesn't expand _at all_ inside the holes. That is, the non- expansion of the hole background carries down hierarchically; you don't need to introduce an expansion term into a metric describing an individual star or planet.

It would be very exciting to find _any_ metric expansion within the solar system, or in another solar system under close scrutiny, or at any scale smaller than that of the swiss-cheese "holes".

Since real matter systems like stars and planets can be very well described as a "hole" generating a metric like Schwarzschild out to some boundary, there is no motivation to add in a metric expansion term (it would just vanish within the boundary).

Finally, inhomogeneous cosmologies generally import these results, just like they import the local and global measurements of H_0. The viable scale of fluctuations in the Hubble parameter in such approaches is large compared to solar systems. So there's no relief in a "well, your model is wrong" (incidentally, I'd agree, there are some real problems with swiss-cheese).

In summary, the evidence is against your claim, and other strands of evidence support theoretical frameworks in which there is _no_ metric expansion around Earth/Earth-Moon. That includes frameworks in which one has explicit terms for such expansion: those terms must vanish around here.

\- --

See also: the much less wordy way of taking the same position at [http://curious.astro.cornell.edu/about-us/97-the- universe/ga...](http://curious.astro.cornell.edu/about-us/97-the- universe/galaxies/cosmology/538-as-the-universe-expands-why-don-t-galaxies- get-stretched-out-intermediate)

Compare: [https://medium.com/starts-with-a-bang/ask-ethan-if-the- unive...](https://medium.com/starts-with-a-bang/ask-ethan-if-the-universe-is- expanding-why-arent-we-71b46b5e9974)

<comment><USER43> I don't think this is correct:

"Grossly, 0.07 nanometers per metre per year expansion everywhere would be impossible to hide from solid state physics, and even several everyday polymers and ceramics; an expansion term would have to appear in accurate descriptions."

On a small scale, the effects of the expansion are overcome by other forces -- this doesn't mean that the expansion doesn't occur - merely that its effect is locally overcome and so it doesn't pull apart arrangements of atoms and molecules which are bound together by other forces.

This is even described in your second link.

<comment><USER41> My model was the following. Take the classical rubber sheet, place two marbles on it, then stretch the rubber sheet. The marbles are unbound and therefore expand away from each other with the expanding rubber sheet. Now connect the two marbles with a spring and again stretch the rubber sheet. The rubber sheet expands everywhere just as before but now the spring prevents the marbles from being pulled apart and makes them slip across the rubber sheet.

I can see where this model might be misleading or go wrong, it requires some friction between the marbles and the rubber sheet because all massive things are bound together at least by a tiny force and without friction the weakest imaginable spring would still prevent the marbles from separating. I have to think about this more carefully and try to figure out how badly this affects the model, maybe it's actually a really bad model.

But as far as I can remember, whenever raattgift said I am wrong, I was wrong. So I will reserve some time this evening for trying to work through his answer. I also skimmed the Ask Ethan article and at least at first it sound like what I intended to say, especially the following paragraph. On the other hand I did not notice any of raattgift's points in this article on a first quick pass.

 _The reason for this is subtle, and is related to the fact that the expansion itself isn't a force, but rather a rate. Space is really still expanding on all scales, but the expansion only affects things cumulatively. There's a certain speed that space will expand at between any two points, but if that speed is less than the escape velocity between those two objects — if there's a force binding them — there's no increase in the distance between them. And if there's no increase in distance, that impetus to expand has no effect. At any instant, it's more than counteracted, and so it never gets the additive effect that shows up between the unbound objects. As a result, stable, bound objects can survive unchanged for eternity in an expanding Universe._

<comment><USER42> Your italicized paragraph is a good clue.

I started a reply which was getting too long and technical, with the aim of looking at three prongs. Post-Newtonian elements are at work, and it is easy to fool oneself thinking of the underlying one: metric gravitation and how it manifests within extended objects. (It _does_ ; we can see that from the figure of the Earth and its internal structure, and from other roundish celestial bodies.) Where self-fooling is easiest is in thinking (1) in terms of forces, (2) using too large a set of local coordinates or inappropriate coordinates, and (3) studying an object that extends beyond the boundaries of "local".

I have some things to do but will return to your comment and its parent in a few hours with a more detailed comment that hopefully won't stray off into the weeds of technicalities. :D

<comment><USER41> After reading the Karen Masters link and your first response a few times, I think I am starting to understand what you want to point out. If the universe were empty and expanding, then some light non-interacting test dust would indeed get pulled apart everywhere and at all length scales. But when we add matter and let it collapse, the collapsing matter kind of pulls spacetime with it as it collapses and may eventually reach a kind of equilibrium where the effects of the expansion and the collapsing matter cancel out locally leading to a non-expanding region. If this is kind of correct, I have a very wrong model of the effect of mass on spacetime and have to rewatch Susskind's lectures on general relativity.

<comment><USER42> Yes, good, you've saved me some typing along these lines. (Well, in retrospect, maybe not that much :D )

In typical vacuum solutions of the Einstein Field Equations the metric is what determines the available geodesics[0]. Putting an isolated object into a vacuum solution causes it to "select" an appropriate geodesic from the ones available, and if left alone, that object will at every time be somewhere on that geodesic. A "test object" is pointlike and massless, so adding it to the vacuum does not change the background metric at all. But if we make it heavier, or bigger and rotating or oscillating, then the spacetime is no longer exactly modelled by the vacuum solution. At that point one might use perturbation theory, and consider the vacuum metric as a background and the metric the not-quite-a-test-object itself generates as a perturbation field overlaid on that.

The algebra usually looks like g_{\mu\nu} = \eta_{\mu\nu} + h_{\mu\nu} where the greek subscripts are the usual indices running 0,1,2,3 in 4-dimensional Lorentzian spacetimes (like ours, and most that you'll ever run into), \eta is the chosen background field, h is the perturbation field, and g is the "true" metric. One can also add perturbation fields or play around with higher-order contributions from self-interactions (say if the not-a-test-object is a black hole binary, or a solid fragment of a supernova (an Earth-massed blob of hot metal?) moving relativistically).

If we start with an expanding Robertson-Walker spacetime _vacuum_ (no matter, not even dark matter), and add a single galaxy cluster, we need to figure out the metric to see how it evolves (or to see what geodesics are available for test particles we throw in as probes).

We can do this in a couple of ways: either using perturbative methods like above, e.g. g = {RW} + {galaxy}, or start with a single g for the whole spacetime from a known set of appropriate solutions like Schwarzschild-de Sitter or Kottler, or by engaging in "inside"/"outside" stitching together of metrics like I described earlier (swiss-cheese). (There are other approaches too!)

Each has advantages and drawbacks.

The middle option has the problem that a galaxy cluster will only look like a Schwarzschild source from so far away that it shrinks to a point. Closer observers will see (optically, even!) that it's lumpy, and if they have sufficiently sensitive gravimeters or a probe like Synge's "five-point curvature detector" they will see that Schwarzschild is not quite accurate. In particular, the geodesics the components of the gravimeter or probe "find" are not the ones that would be generated in the model metric.

The first option is hard to do and usually leads one into numerical relativity. That's not such a bad thing these days, thanks to modern codes and supercomputers. However, it's often hard to extract intuitions from numerical solutions, and even harder to boil down into an explanation for others ("just run this code and you'll see" is not very satisfying).

The last option has been around for decades and is a bit half-way. Its advantage is that you generally can say intelligent things about what's going on far from the thin shell boundary, and can develop a good map between the evolution of the configurations of matter within the "inside" metric and that outside. Its disadvantage is that it is a painful amount of work that computers aren't very good at helping with yet.

Which one chooses will depend on some combination of the problem being studied, personal preference, and trade-offs between manual work, accuracy, and comprehensibility. One can combine the perturbation approach with the inside/outside approach, so that one has (dropping the indices) g_{outside} = \eta_{outside} + h_{outside} and g_{inside} = \eta_{inside} + h_{inside} and an Israel-Darmois junction between g_{inside} and g_{outside} which is at least in principle something one can think about functionally (a test object crossing the junction will have its momentum altered; if it just drifts across, the junction is something like a "kink" linking two otherwise smooth geodesics).

Now, back to the standard cosmology, using the "inside"/"outside" approach. In the "outside", the Robertson-Walker vacuum does just what you say:

> [as the] universe [is] empty and expanding, then some light non-interacting > test dust would indeed get pulled apart everywhere and at all length scales

and then

> But when we add matter and let it collapse

... we can no longer describe the whole spacetime as a Robertson-Walker vacuum that we're simply probing. Our matter perturbs the RW metric, so the true metric g must be the combination of RW and whatever metric the introduced mass generates. Since the introduced mass is collapsing, it's probably approximately described some sort of Tolman dust. So we select e.g. the Lemaître-Tolman-Bondi metric and perturb that in turn, so g = RW + LTB + O(h) + O(h^2) + ... where h is the deviation of the matter we introduced from exact LTB, and h^n is higher-order perturbations.

This g, like any other metric, will generate a set of geodesics throughout the spacetime. If our collapsing matter was a dust, then each of the individual particles will select its own metric. Flashes of light will find their own null geodesics determined by the metric, and so forth. The results are different from Robertson-Walker, at least close to the matter that we introduced. At even fairly short distances the higher order terms in h fall into irrelevance, and at large distances h itself becomes negligible.

I want to write a bit about extended objects, but that'll have to wait until a bit later. The key feature there is that the individual components of such objects are stuck together, so they don't find their own individual geodesics. The behaviour of extended objects in curved spacetime is fun!

> may eventually reach a kind of equilibrium where the effects of the > expansion and the collapsing matter cancel out locally leading to a non- > expanding region

You can move the thin shell of the junction around to explore that kind of thing. Or taking a purely perturbational approach you can look for regions of spacetime where geodesics have the characteristics you want (drop down test objects near point in spacetime near a suspected "cancelling-out" region and see if the inertially-moving test objects eventually collide or separate).

How you represent what's happening there is up to you. You could use your colloquial expression, a line from the Karen Masters link or something like it, or talk about the mathematical structures. The theory underdetermines the precise mathematical expression (there are lots of exactly equivalent ways of writing it down, and lots of so close it doesn't matter approximations); the English has it even worse. :/

However, the key thing is that exact vacuum solutions stop being exact when you add matter. Matter rarely cooperates with exact non-vacuum solutions (they typically are maximally symmetric: spherical arrangements of matter of uniform density, with no multipole moments from internal motions, etc. which is far from what we see measuring Earth's or Moon's gravitational fields with e.g. GOCE and GRAIL, and solar prominences big and obvious, galaxies can be spiral, a tiny black hole orbiting a large one will induce tides on the large one, and so on.)

\- --

[0] I'm deliberately going to avoid talking about non-geodesic trajectories through spacetime for now. May come back to that when discussing extended objects in a followup.

\- --

ETA: I should add that the _metric_ expansion is not really an expansion of space, but rather an extra term tacked onto the metric g. So following the perturbation notation above we could start with flat spacetime \eta and say g = \eta + {expansion} and end up with g = {expanding Robertson-Walker}.

This is quite common: the "true" background is Minkowski flat-space, and then the vacuum eternal spherically-symmetric black hole is a perturbation on that, and then there may be other perturbations. (Instead of starting with the "true" background of Schwarzschild.) This kind of thing leads to some insights about asymptotic flatness.

So for an expanding cosmos, we can start with a perfect flat non-expanding one and perturb that, expanding the _metric_.

(This is being really loose with terminology, but I think gets the point across reasonably. It's the metric expansion of space because there is a time parameter in the line-element of the metric; _spatial_ distances are determined by _when_ (coordinate-time) you are. g = \eta + f(t), where f is a function taking a time coordinate and generating a perturbation field; maybe better to write g(t) = \eta(t) + f(t) where g(t) is the metric's _spatial_ distance functions for all events on a slice of space that where everything is at the same time coordinate t; but this dives into 3+1 spacetime splittings which is another big can of worms...).

\- --

ETA2: the Overview section of this puts it well in a different way. (No claims about the other sections, I haven't read them yet.) [https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/m/Metric...](https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/m/Metric_expansion_of_space.htm)

<comment><USER42> A couple little things I won't turn into literal ETA3, just in case you've already been reading the long post above. :)

(2) below is also mostly for me, I think.

1\. Thanks, Michael Weiss. This is essentially the same argument I'm making, only terser. [http://math.ucr.edu/home/baez/physics/Relativity/GR/expandin...](http://math.ucr.edu/home/baez/physics/Relativity/GR/expanding_universe.html)

2\. One important thing about the expansion of the universe is that people hear "expansion of space" and reasonably think space has physical properties. [https://arxiv.org/abs/0707.0380](https://arxiv.org/abs/0707.0380) is a good rant about that, and [https://arxiv.org/abs/0809.4573](https://arxiv.org/abs/0809.4573) is another interesting take. There's a sort of Betteridge effect going on, in that none of the authors think that the concept of expanding space is awful, but they're instead capturing the "gotchas" that befall even working relativists stray into what philosophers call manifold substantivalism. (I hope that doesn't attract house philosophers, no offence. I don't think my text is all honey!)

<comment> delta-v Could I interpret it this way?

In the EFE, if we move the cosmological constant factor to the right handside, where the stress–energy tensor is, then stress–energy tensor and the cosmological constant factor have opposite signs and stress–energy tensor can overcome the cosmological constant factor.

When we say EM-forces/Strong/Weak forces "cancel out" the expansion of the universe, it isn't because of those forces are holding matters together. But they contribute to the stress–energy tensor and "offset-ed" the effect of the cosmological constant factor.

Even without those forces, as long as the stress–energy tensor is greater than the cosmological constant factor, the solution of EFE will be non expanding.

Does this sound right to you? Thanks.

<comment><USER42> Well, so you write down an initial values surface with that approach and let the matter evolve: either you get something physically plausible or you don't. We have some guides as to what is physically plausible, and of course evidence that any of them is wrong would be very interesting.

More theoretically, the LHS doesn't care about how you arrange the RHS at all. More finely, the metric does not care how you compose the metric. If you do it perturbatively, the leading term could be Minkowski or Gödel for all it cares, as long as the sub-leading terms then present a useful background for small perturbations that remain small (or better, vanish) rather than explode into large perturbations. Inside the solar system, Schwarzschild gets that right, and nobody has shown you need to correct for the global behaviour of the cosmic expansion.

> ... if we move the cosmological constant factor to the right handside ..

Before the 1920s (!) there was a discussion about where to put an everywhere isotropic tension in the EFEs. [https://arxiv.org/abs/1211.6338](https://arxiv.org/abs/1211.6338)

In section 3, the author quotes Einstein's response about how to determine the density. The part after, "Later, he finishes with..." seems especially germane, and cf. section 4 especially its last sentence (wherein "dark energy" in that context means a source field with a potential and dynamics and a coupling to the other source fields and a set of initial values).

[Heh, typo in the second sentence of the last paragraph of §3, "vale" instead of "value".]

> (matter forces) contribute to the stress-energy tensor

Ok, but if you hold that the CC acts isotropically everywhere you can think about decomposing the curvature tensor into its Ricci (and Weyl) components. Weyl tensor encodes the stretch-squash astigmatism: a spherical volume in the presence of a nonvanishing Weyl start to look more like a U.S. football. Ricci scalar encodes the isotropic change in volume. For a volume, nonvanishing Weyl with a vanishing Ricci is volume-preserving; a vanishing Weyl and a nonvanishing Ricci is a contraction or expansion.

The cosmological expansion at cosmological scales clearly is Ricci scalar rather than Weyl, since matter in the large remains isotropic and homogeneous.

Shuffling \Lambda over to the source side does not change that observation: we don't see broken cosmological-scale isotropy, so we must still have a vanishing Weyl and a nonvanishing Ricci scalar on the LHS. How does that happen? Presumably in the metric, since it's the obvious choice of dynamic field (although of course you could insist on making the RHS as complicated as you like, and there have been cases where having the metric maximally static with gravitational dynamics shuffled into "fake" matter is useful -- the original Hawking Radiation paper did just that, for instance; and of course you might want a quintessence-style field instead of a CC, and bite the bullet on recovering observations through that field's behaviour).

Ultimately what we care about is that we have the correct EOMs, and for test particles the EOMs in our labs and in our experimental platforms elsewhere in the solar system, and observed for astrophysical objects throughout our galaxy and the cluster it's in, are nowhere near the EOMs of FLRW. They are _much_ nearer to Schwarzschild.

</comment></comment></comment></comment></comment></comment></comment></comment></comment></comment></comment><comment><USER44> My favorite bit from the author on Twitter: [https://threadreaderapp.com/thread/1070302359325151233.html](https://threadreaderapp.com/thread/1070302359325151233.html)

> The next-generation radio telescope - the Square Kilometre Array > @SKA_telescope will be able to test this theory, and directly confirm or > invalidate its predictions. 13/17 It is rather surprising that the model > predicts the properties of a LambdaCDM universe.

As a casual observer this is is what gets me excited! We'll get our answers one way or another.

</comment><comment><USER45> Presumably you could describe this as a theory of levity. For happy spacetimes.

</comment><comment><USER46> The possibilities for Star Wars puns are endless.

There are alternative explanations that theorized that the 2nd law is not linear for extremely weak forces.[1] Thus, two masses that were sufficiently far apart would experience an attraction larger than that predicted by an inverse square law.

I think some particular applications of these theories were proved wrong some years ago, but I can't find those results.

[1] [https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics](https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics)

<comment><USER47> Actually, Star Trek had an episode where a giant space amoeba pulls the Enterprise into a "zone of darkness" where thrust towards the amoeba pushes the enterprise away from the amoeba. Sounds similar. Of course they destroyed the creature with some antimatter.

[https://en.wikipedia.org/wiki/The_Immunity_Syndrome_(Star_Tr...](https://en.wikipedia.org/wiki/The_Immunity_Syndrome_\(Star_Trek:_The_Original_Series\))

</comment></comment><comment><USER48> Negative mass... holy shit with this we could break the speed of light

<comment><USER49> How?

<comment><USER48> By offsetting the mass of a system, to produce a zero mass vehicle.

<comment><USER50> Take a net negative mass vehicle, and accelerate it by having it collide with its propellant. Would this be an anti-rocket?

<comment><USER48> How does it come to a stop, the vehicle gains too much mass?

<comment><USER50> The mass part of the vehicle could either detach from the negative mass component. Or the vehicle could eject mass to reduce velocity.

</comment></comment></comment></comment></comment></comment><comment><USER51> "Negative masses are not a new idea in cosmology. Just like normal matter, negative mass particles would become more spread out as the universe expands – meaning that their repulsive force would become weaker over time. However, studies have shown that the force driving the accelerating expansion of the universe is relentlessly constant. "

Is it though? How can you measure a universe-size force that takes billions of years to "move" on a human lifetime scale?

</comment><comment><USER52> Not a physicist. If negative mass exists, is it featureless, or is it composed of units which can combine to form analogous negative mass atoms, negative mass molecules, etc?

<comment><USER53> It would presumably be composed of units which could well join together into larger structures. But these would have to be small scale (the size of atoms or molecules) because gravity causes negative masses to move away from each other. So it wouldn't clump together into planets and galaxies.

</comment></comment><comment><USER54> Would this also explain galactic voids as regions of large negative mass? It would seem that deviations in the Hubble constant bear a void would confirm this theory.

</comment><comment><USER55> > Negative masses are a hypothetical form of matter that would have a type of > negative gravity – repelling all other material around them. Unlike familiar > positive mass matter, if a negative mass was pushed, it would accelerate > towards you rather than away from you.

That assumes that inertial mass = gravitational mass, which is assumed to be true, not not proven.

<comment><USER56> > That assumes that inertial mass = gravitational mass, which is assumed to be > true, not not proven.

The assertion has been tested experimentally. Inertial and gravitational mass are seen to be equivalent within the bounds of experimental accuracy. The wikipedia article on the "Equivalence Principle" has lists of tests for various versions of the principle: [https://en.wikipedia.org/wiki/Equivalence_principle#Modern_u...](https://en.wikipedia.org/wiki/Equivalence_principle#Modern_usage)

<comment><USER55> And the negative mass postulated here? We don't know if it's still equivalent there because we have never tested it.

It would be a lot simpler if inertial mass was negative gravitational mass in this theory.

Then you have repulsive gravity with normal behavior under force.

<comment><USER56> I see I misunderstood that you were specifically questioning the equivalence for this postulated negative mass. I thought your statement was a more general one.

</comment></comment></comment></comment><comment><USER57> I love the choice of the word "could" for this title. Makes it sound like the plot for a science fiction book X-D

</comment><comment><USER58> Here comes the Alcubierre Warp Drive!

<comment><USER59> To quote the author [https://twitter.com/Astro_Jamie/status/1070343971338153984](https://twitter.com/Astro_Jamie/status/1070343971338153984)

> It is quite likely that the negative masses in this study are a mathematical > tool, rather than real physical matter. This rules out a lot of sci-fi, > which is disappointing of course!

<comment><USER35> To be clear, the author IS proposing that there MAY be negative mass particles, not that this is all mathematical. That statement was simply a tip of the hat to the fact that none have yet been detected and its possible his theory is just a "accurate way to model" dark matter/+dark energy. It's just a nice way saying "My thoery might be the Newtonian Mechanics of Dark Matter/Energy, close but possibly wrong."

Why crap on the fact that this may lead to a warp drive.

</comment></comment></comment><comment><USER60> Reminds me of this (very old) theory of gravity: [https://en.m.wikipedia.org/wiki/Le_Sage's_theory_of_gravitat...](https://en.m.wikipedia.org/wiki/Le_Sage's_theory_of_gravitation)

<comment><USER61> Non mobile link: [https://en.wikipedia.org/wiki/Le_Sage's_theory_of_gravitatio...](https://en.wikipedia.org/wiki/Le_Sage's_theory_of_gravitation)

</comment></comment><comment><USER62> No problem with negative masses, but where does this continuously generated fluid come from?

</comment><comment><USER63> I'm confused.

From the article:

"This is explained by the Hubble-Lemaître Law, the observation that more distant galaxies are moving away at a faster rate."

If we observe an accelerating universe how can be that galaxies in the past move away at a faster rate?

<comment><USER64> Because more and more negative mass fills in the space left behind by the expansion creating further expansion?

<comment><USER65> why would negative mass fill in the space rather than just "zero mass?"

<comment><USER64> Negative mass has greater pressure to displace vacuum in a similar way that mass does? That was my assumption. Perhaps not!

</comment></comment></comment></comment><comment><USER66> If we can prove that dark matter exists with negative mass, this may pave the way for fundamental research on other phenomena with negative mass, like anti- gravity effects.

</comment><comment><USER67> If you put a negative mass and positive mass side by side and release from rest, they will accelerate indefinitely and break conservation of energy. Of course science should be open to any possibility, no matter how strange. But I feel the author understates its strangeness. And requiring negative mass to be continually created makes this theory not all that much "simpler" than the standard dark matter+dark energy.

<comment><USER68> They would accelerate indefinitely, but it wouldn't break conservation of energy. Gravitational force is inversely proportional to distance^2, so potential energy (integral from 0 to infinity of Force dx) still converges to a finite number.

Same with normal gravity, but backwards.

<comment><USER21> I think the weirdness is, the distance between masses wouldn't change, they'd just accelerate together, in the same direction, indefinitely.

Both mass would experience negative repulsive force:

F=Gm(-m)/r^2

=-Gm^2/r^2

The positive mass accelerates away from the negative mass, because F=ma

=> ma=-Gm^2/r^2

=> a=-Gm/r^2

Now here's the kicker. If inertial mass (the m in F=ma), is the same thing as gravitational mass. Then, _the negative mass accelerates towards the positive mass_. Because

F=(-m)a

=> F=-ma

=> -ma=-Gm^2/r^2

=> a=Gm/r^2

So accelerates in same direction as positive mass.

Technically, conservation of energy & momentum is maintained, because the negative kinetic energy of negative mass would cancel out positive energy of positive mass.

But I think the above can't be natural, because the magnitude of kinetic energy would grow to infinity, leading to even more impossibilities.

So you'd need to 'hack' the theory of gravity and make inertial mass different to gravitational mass. So the particle has negative gravitational mass, but positive inertial mass, to make laws of physics stay sane :)

<comment><USER5> From what I gather, the negative mass repels the positive mass (which is thus accelerated _away_ ), and the positive mass attracts the negative mass, which (because it has negative mass) is thus also accelerated _away_.

Now, the kinetic energy of the positive mass grows, but the kinetic energy of the negative mass is negative and falls (because its mass is negative...), so energy is conserved.

EDIT to add: I think I gathered wrong. Apparently, there is runaway motion (same direction), energy and momentum is still conserved (since one mass is negative), and since total mass is zero, the two particles reach speed of light. Intriguing. See paper.

</comment></comment></comment></comment><comment><USER69> Could this repulsive 'Dark Fluid' be what they use on the Enterprise to generate artificial gravity? They could pipe the stuff through the ceiling to press you down against the floor. But that would make the gravity point the wrong way in the decks above and below. But if they alternated the direction of "up" on each deck, maybe they would cancel each other out.

</comment><comment><USER31> Completely a layperson who's only read science for the masses type physics and astrophysics, but now imagine that there are all sorts of undiscovered phenomena that are actually just the inverse of existing properties of nature we know. Does that make sense, or resonate with more rigorous scientists, Reade archers, students?

</comment><comment><USER70> Negative mass is required to produce warp drive... We might not be stuck here forever

</comment><comment><USER71> Does his theory explain the Bullet Cluster and baryon acoustic oscillations?

</comment><comment><USER72> Dark fluid, negative mass?

Rubbish, it's turtles all the way down!

</comment><comment><USER73> Anyone read up on David Wiltshire's timescape model?

After reading it, I became more skeptical of dark matter and dark energy theories as the cause of the Universe's apparent accelerating expansion.

</comment><comment><USER74> Could be made into a nice Landspeeder!

</comment><comment> time-domain0 Neither an experimental physicist nor cosmologist, but another possibility is that our universe shares very slight space-time interactions with other universe(s) in a multiverse where its mass-energy casts negative mass "shadows" in ours. Blackholes in one creates areas of repulsion and expansion in the other. Maybe this is where the missing mass-energy is? It's there, but it's not in our universe.

</comment><comment><USER75> How abstract concepts, introduced to establish artificial symmetry, could be used to describe aspects of reality which does not rely on any abstract notions whatsoever?

Some processes are symmetrical to an outside observer, which does not imply that anything must be or should be symmetrical. It is an observer's preference to see symmetry everywhere.

There is no such fucking things as "dark" liquids or negative "masses" merely because a model superimposed on reality have nothing to do with reality itself.

The impossibility is the same as the principal impossibility of revealing the CPU's actual wiring from the level of code it runs. There is not a single fucking way to do it in principle, no mater what fancy guesswork one would use or what kind of a wrongly simulated model one will superimpose on what one is able to "see" and examine.

This is not even science, but some sort of contest of abstract theology, crafted to please fellow reviewers and sectarians.

</comment><comment><USER76> Alright question for all you genius physicists- what makes you visit this forum which is primarily a discussion board for news and startups (primarily)in the field of Information Technology? I'm curious because I don't know you're your domain intersects with this forum's.

</comment><comment><USER77> Eezo?

</comment><comment><USER78> A "dark fluid" with negative mass COULD dominate the Universe, sure.

But so could galactic-scale electric currents and magnetic fields, and is more likely.

No one ever talks about that.

<comment><USER79> Both these are real things we measure with radiotelescopes.

They are not strong enough to produce the necessary effects, they are however interesting phenomena - [https://arxiv.org/pdf/1302.5663.pdf](https://arxiv.org/pdf/1302.5663.pdf).

<comment><USER80> The biggest tell that the Electric Universe theory is bunk is that anybody who ever talks about it can't hardly get two sentences in before dropping in the "but nobody ever talks about magnetic fields or electric currents at this scale"... which is easily observed to be utterly false. Astrophysicists talk about it a lot, and you can find even more discussion if you add "plasma" to the search terms.

If Electric Universe advocates are so wrong about something so easy to check, it doesn't give me much reason to check out anything else they say. (The fact that I have done so nevertheless and I've never managed to find them making an actual prediction is another. It seems to be one of those recursive handwave theories that never quite lands on anything concrete no matter where you search, but it sure does know that the standard theory is wrong.)

</comment></comment></comment><comment><USER81> Then we are definitely in a simulation. That is the fabric that holds the universe together.

<comment><USER82> That's a complete non-sequitur.</comment></comment>


SHOW HN: Gadget Explorer – fun little way to find cool gadgets - <AUTHOR> http://www.digitpedia.com/gadget-explorer/ <comment><AUTHOR> I only had access to my laptop for a week so with all my work on my PC I decided to create a minisite that was just a bit of fun, it's fairly useless, that is unless you want to buy something random, like a gold vacuum for £800,000. I felt the existing content top lists (you know the type '21 most craziest gadgets in the world') of gadgets aren't that nice to use and this was a better way to discover cool gadgets. Nothing special to this from a design or creation point of view, built with Wordpress and then I used a blank theme to customize it myself. But I enjoyed making it and I hope people find it a nice experience.</comment>


Clair v2.0: the container security scanner, now with Alpine Linux - <AUTHOR> https://coreos.com/blog/celebrating-clair2.0 <comment><USER2> if you spelled it with a y, your security measures could involve flooding rivers to overrun botnet zombies!</comment>


W3C give up on preventing PWAs from tracking users - <AUTHOR> https://www.theregister.com/2020/07/31/w3c_progressive_web_app_privacy/ <comment><USER2> A PWA has lots and lots of issues regarding trackability. start_url is just a very minor part of that. An application that is actually a weird website will be able to track you, there will be Javascript with tons and tons of attack surface for this.

If you don't want tracking, use proper local applications and deny them network access.

</comment><comment><USER3> This smells like a story Apple shopped out to keep defending their 30 percent racketeering operation. PWAs are better than native apps for privacy and security in almost every single way.

</comment><comment><USER4> There are so many more ways to track you, not sure why the fuss about PWAs which almost noone is using.

For example you can just use WebGL for fingerprinting the browser.

</comment><comment><USER5> Once again proving W3C is absolutely useless.

</comment><comment><USER6> A great opportunity for Firefox to implement PWAs with privacy protection and use it as main selling point.

<comment><USER2> The only winning move is not to play. The only privacy-preserving PWA doesn't have network access. Which excludes the 'W' part...

<comment><USER7> Just disconnect your phone from the internet.

Native apps aren't much better. The real solution is to use FOSS apps that you can check yourself and trust regardless of pwa or native.

Your browser and device already had APIs to track you long before PWA standard and they still do.

[https://arstechnica.com/gadgets/2020/06/tiktok- and-53-other-...](https://arstechnica.com/gadgets/2020/06/tiktok-and-53-other- ios-apps-still-snoop-your-sensitive-clipboard-data/)

[https://www.theverge.com/2020/7/25/21338151/instagram-bug- ca...](https://www.theverge.com/2020/7/25/21338151/instagram-bug-camera- privacy-ios14-apple)

[https://github.com/facebook/facebook-ios- sdk/issues/1374](https://github.com/facebook/facebook-ios-sdk/issues/1374)

[https://github.com/facebook/facebook-ios- sdk/issues/1427](https://github.com/facebook/facebook-ios-sdk/issues/1427)

</comment></comment></comment><comment><USER8> Why can't they refetch the manifest.json when cookies are cleared? That would give it a new ID.

<comment><USER9> Then you are just pushing where the uuid is stored up stream another step.

In order to refetch the manifest you will have to remember it's location. Just use /<uuid>/manifest.json as the manifest location and have the server inject that into manifest file when fetched.</comment></comment>


Beautiful Image Hover Effect Using Only Webkit CSS (No JS) - <AUTHOR> http://www.nikesh.me/blog/2010/05/sexy-image-hover-effects-using-css3/

<comment><USER2> The dark box flipping around on top of the picture seems gratuitous and pointless. It'd be a nicer effect if the picture just zoomed and became brighter.

<comment><USER3> I totally agree, I'm guessing that the example included that just to demonstrate what was possible as each picture had a different dark box effect.

Other than that, this looks awesome, at least in Chrome on Mac.

</comment></comment><comment><USER4> There is a big flaw in CSS3 implementation of animation:

If the animation is interrupted midway (i.e the animation happens on :hover, and the user moves the mouse away), the reversed animation always takes the same amount of time. This can result in the reverse animation proceeding at different speeds (try setting the -webkit-transition-duration to 5s, and hover your mouse over the element for just a second).

Instead, the browser should precisely reverse the animation it has already played, e.g. if half the animation has already occured, for 0.25 seconds, the reverse animation should similarly last only 0.25 seconds.

<comment><USER3> The example in the linked article behaves exactly as you describe, at least in Chrome on Mac. If I just fleetingly hover over something, it pulses up and down at the same speed for the same amount of time. It just looks _right_.

</comment></comment><comment><USER5> Yeah, but how is that going to work in the iPad _since it has no hover?_

</comment><comment><USER6> Nice demo, but I feel that the title is a little misleading as the CSS is more so webkit-specific CSS than it is CSS3.

</comment><comment><USER7> When I looked at the markup, I thought, "I would use JS to insert those mask divs." Does anyone else feel that same base compulsion to keep the markup clean?

<comment><USER8> Not really. Using JavaScript to add mask <div>'s is a messier solution, requiring more KB of code, especially if you want it to work on all browsers, even those that don't properly support DOM manipulation. Also the JavaScript would have to run after the other parent <div> has already been downloaded and rendered, meaning that there would be a brief time when there was no mask.

In my opinion, it is just easier and cleaner to add an extra <div> to the code than to add a bunch of extra lines of JavaScript to do the same thing.

<comment><USER7> Just so I'm not missing something, are there browsers which would support the Webkit CSS but not support DOM manipulation? Or are you concerned with people running NoScript style plugins?

Not being hostile, just want to clarify.

<comment><USER8> Yes, NoScript is a problem. However, I was referring to other scenarios in general where a problem can be solved by just adding a <div> in HTML code. It seems more economical to me to add the <div> manually to the HTML code as in this Webkit example rather than writing a JavaScript routine to manipulate the HTML code at runtime on the client's machine as you suggested.

</comment></comment></comment></comment><comment><USER9> I'm not sure you can call _-webkit-transition-duration_ CSS3.

That said, the animations are really just sugar, and would be painful in any browser that doesn't handle them very fast (I used to hate lightbox). Since the effect may still be worthwhile without them, and purdy with them, I prefer this to javascript.

<comment><USER10> I do agree with the usability concerns. The less animation the better, imho. If you remove the animation component that almost all "lightbox-like" implementations use, it's quite a handy feature tho.

But then again, I guess the point of the article was about showcasing what one could achieve with CSS alone.

</comment></comment><comment><USER11> Arrrrg he used only the -webkit hacks and did not put the actual CSS3 commands for other browsers.

i.e. -webkit-box-shadow:0px 0px 30px #ccc; should have box-shadow:0px 0px 30px #ccc; and so on. It just ruined the entire article..

<comment><USER12> It is just an example to show how differently we can use CSS3 transition property ... I don't think it ruined the entire article..

<comment><USER13> No, I completely agree. But I work with some CSS purists and they would probably think the same thing. Ruined I tell you ! RUINED !

<comment><USER14> CSS purist should learn that vendor prefixes are not hacks.

</comment></comment></comment></comment><comment><USER15> This looks nice, but could someone remind me, why is CSS better than JavaScript for this kind of functionality?

<comment><USER16> The advantage of doing it in CSS is that browsers can implement animation themselves.

Animation in JavaScript is a bit of a hack - run a loop with setInterval, change the value of various CSS values for each frame, dynamically adjust the frame rate based on the amount of time left, implement your own easing...

If an animation is described to the browser directly (fade from this value to this value taking this much time) the browser can implement all of the above itself, in a standard way. With access to APIs like Core Animation, the browser can even take advantage of hardware acceleration.

I argue that it makes sense for browsers to provide an animation API. The only remaining question is what form that API should take. It can either be exposed as CSS syntax, or as part of the DOM APIs exposed to JavaScript (document.animateElement(el, ...) for example).

CSS is meant to handle presentation logic, so if you define animation as part of the presentation layer of your site then putting it there isn't really that crazy.

<comment><USER15> Implement the whole animation API in CSS? What if I want the animation to be triggered by button click instead of hover?

<comment><USER17> Handle the click with javascript, adding a CSS class to the element. The class definitions should look like those of :hover in this example.

</comment></comment></comment></comment><comment><USER18> That looks really cool. How big a %age of the mainstream browsers can show this effect?

<comment><USER19> Well since it uses Webkit I guess just Chrome and Safari. It looks like Firefox is behind on animations, although they've implemented transforms now.

<comment><USER18> I'm looking at it using firefox and the highlight seems to work for me.

<comment><USER20> There are some mask effects you're missing. Firefox ignores -webkit-* CSS.

</comment></comment></comment></comment><comment><USER8> Very nice! The code is simple and easy to read as well. Now if only webkit had more thorough coverage in browsers so that we could use these pure CSS effects and know that all our visitors can see them.

<comment><USER3> Effects like this should never be counted on for "all our visitors", it's really more of a progressive enhancement/graceful degradation thing. Example: hover effects won't ever work for people using touch-screen devices.

</comment></comment><comment><USER21> i think we have differing opinions on what is beautiful and sexy.

</comment><comment><USER22> Only for webkit

</comment><comment><USER23> In contrast with what others have said, it works for me in Opera 10.53 in Linux.

</comment><comment><USER24> try moving the mouse around over the images and then look at your CPU graph

<comment><USER25> A quick peak at 25% as soon as I hover and that's it (three year old 15" MBP). Seems kinda tolerable.

</comment></comment><comment><USER26> This could be done without JS for years. The neat part is doing it without images.</comment>


RSSted Development - <AUTHOR> http://american.com/archive/2009/june/rssted-development

<comment><USER2> The article is extremely long and overly articulate, considering it discusses the consumer's preference of _the short, the sweet, and the bitty_.</comment>


I laugh so hard I get tears: Hacker News Onion (Twitter feed) - <AUTHOR> https://twitter.com/HackerNewsOnion <comment><USER2> > Hackathon Developer Gets Development Environment Working With Two Whole > Hours To Go

This one just hits home with anytime I try to program on a different computer.

"Ok, I have 5 hours to program, let's do this" ... 4 hours later ... "Ok, all my sublime plugins and themes are installed, let's start coding!"

<comment><USER3> I don't know if it is good or bad that I don't have an environment I rely on that much

<comment><USER2> ha yeah that was definitely an exaggeration. I don't think many people _need_ a complex environment, it's more about personal preference. If I can do a one- time setup that saves me time on all of my future projects, rather than take longer to complete each project, that overhead is well worth it to me.

</comment></comment></comment><comment><USER4> I made a dumb thing a while ago you can play with to try and differentiate between them and real HN quotes: [http://hack.pizzey.me/](http://hack.pizzey.me/)

It's usually pretty easy due to the predictable format of HN Onion, but when you get one that doesn't follow that form it can be amusingly difficult.

</comment><comment><USER5> >Recruiter mistakenly hires real ninja.

>Team finds this totally sweet until ninja commits seppuku when told to use graphical IDE.

</comment><comment><USER6> Mime type interviewed for the first time.

Says: <comment></comment></comment>


Mast Raises $7M for a Phone Featuring Separate Work and Personal Numbers - <AUTHOR> http://techcrunch.com/2015/10/15/mast-raises-7-million-for-a-phone-service-sales-organizations-will-love <comment><USER2> So, a dialer app with better dual sim features, some of them cloud powered?

<comment><USER3> Impossible to tell from the article, the video or the website. They say it's a "phone" but it seems more like an app. On the other hand, how could it be natively integrated, I didn't think iPhone allowed that.

</comment></comment><comment><USER4> Wow, I worked in mobile telecom billing in the early 2000s and we were talking about doing stuff like this _back then_. I'm surprised this might finally become reality over a decade later. Then again, we were saying that mobile payment would soon be mainstream in the USA back then, too. :/

</comment><comment><USER5> You can do some pretty cool stuff when you're an MVNO. No need for custom dialers (which wouldn't be much fun on iOS anyways).

The system uses inbound calls, calling history and contacts to learn how to handle outbound call. User preferences control the defaults.

Get a call from Fred on the first number, all calls to Fred will use that number. Make a call to Mary with the second number, future calls to Mary will use the second number.

Throw in multiple sets of contacts from your work and personal email accounts and it's going to be pretty smooth.

Full disclosure: the co-founder is a friend. I have no involvement in Mast though.

</comment><comment><USER6> Google voice could have done this if they would just separate their UI by #.

Currently when you switch phone numbers, if you receive a text to number A and reply when logged in as "Number B" \-- you send as Number B.

</comment><comment><USER7> See CellRox ([http://www.cellrox.com/](http://www.cellrox.com/)) they created a phone w/ separate numbers and virtualization enforced separation with easy switching between the two environments.</comment>


'Unique' cannabis compound reverses brain aging in mice - <AUTHOR> https://www.dw.com/en/unique-cannabis-compound-reverses-brain-aging-in-mice/a-44401750 <comment><USER2> Paper: [https://www.nature.com/articles/nm.4311](https://www.nature.com/articles/nm.4311)

Previous discussions; [https://news.ycombinator.com/item?id=14293415](https://news.ycombinator.com/item?id=14293415), [https://news.ycombinator.com/item?id=14583668](https://news.ycombinator.com/item?id=14583668)

</comment><comment><USER3> It feels like we're heading into the Hype Cycle [1] with cannabis-derived treatments/products/cures, with waves of legalization serving as the classical 'technology trigger'.

I say that mostly because, although this is a solid study with interesting conclusions, 'Cannabis does [amazing thing!]' articles are getting more and more common and mainstream, and I think people are primed to accept them, for want of cures and treatments, for desire to justify existing habits (c.f. the now discredited red wine health studies [2]), and because 'medicine with all these great effects was kept down by the powers!' is a great narrative.

Mostly, I'm finding myself mostly curious what, in 15 years, we'll know these compounds are actually good for, and steeling myself for a _lot_ of bullshit and bad science in the meantime.

[1]: [https://en.wikipedia.org/wiki/Hype_cycle](https://en.wikipedia.org/wiki/Hype_cycle) [2]: [https://www.scientificamerican.com/article/red-wine- research...](https://www.scientificamerican.com/article/red-wine-researcher- implicated-misconduct/)

</comment><comment><USER4> I just don't like anything with 'stoned' effect. Pot, too much alcohol, ketamine.. I can`t find the point in being stoned or to lower my thinking capabilities. Stronger opiates I would never ever try because there is no point besides running away from some problem that should be confronted. With the help of psychedelics maybe? :)

<comment><USER5> My experience is not lowered thinking abilities, but different thinking abilities. If you conceptualize thinking as traversing a graph of thoughts, 'uppers' enhance depth-first traversal, THC enhances breadth-first traversal. This can be a useful mode for generating ideas.

<comment><USER6> What type of mix even is that?

<comment><USER7> That sort of question is highly personal. I've heard many, many people espousing the virtues of some strain of weed or other (eg claiming it helps you think and doesn't make you fall asleep so much) but I've never actually found one that doesn't primarily make me sleepy. I do have access to an enormous variety to try (and I've definitely done my due diligence, so to speak). This has led me to believe that for some people, some strains work differently than for others. This meshes well with my observation that everyone seems to have different recommendations.

<comment><USER8> Have you ever tried a low dosage via vaporization?

Smoking itself, because of carcinogens and oxygenation, will lead you to the sluggishness many people associate with kush.

Fuck smoking. /rant

<comment><USER7> I've tried a low dosage via vaping yes. It still made me drowsy. I can't really smoke anything because my lungs respond poorly, so I generally use tinctures/edibles (if I use at all).

<comment><USER8> Awesome. Well, since we're all trying so hard, I'll throw out one last idea for you: the strain blue dream. One or two hits of that vapor is sufficient for me!

Wishing you the best.

</comment></comment></comment></comment></comment></comment></comment><comment><USER9> Delta 9 THC is the most common compound in the cannabis plant comprising up to 35% of flower weight. Title is...strange. I was expecting to read about some minor accessory cannabinoid.

<comment><USER10> You seem to have confused "unique" with "minor". Delta 9 THC may be common in cannabis, but it is unique to cannabis. The title isn't weird at all.

Also, delta 9 THC may be the most common cannabinoid in cannabis (well, in one of three major chemotypes), but it's not the most common compound in the cannabis plant.

</comment></comment><comment><USER11> If progress in technology continues at this pace, in a few years we will be able to indefinitely extend the life of mice.

<comment><USER12> So… The first immortal mice might have already been born.

Imagine being a mouse living forever in a small glass box in a longevity museum.

<comment><USER13> Sounds horrible to live forever in a glass box

<comment><USER14> Depends how stoned you are.

</comment></comment></comment></comment><comment><USER15> Too bad it gives me panic attacks.

<comment><USER16> You're most likely overdosing -- something that's very easy to accidentally do with the crazy strong pot out there these days. It's even easier to overdose for newbies who have basically no tolerance and often mistakenly think they have to smoke a full joint (or even just a full big puff of some strong pot) to get high. That's probably way, way too much.

If you are willing to give it another chance, you could try finding the weakest pot you can find, then smoke the tiniest amount you can. If you feel nothing, wait a couple of days and try again, this time taking a tiny bit more.

Repeat as needed until you very slowly and gradually work up to a dose that gets you very mild, positive effects, and no paranoia or other symptoms of overdose.

<comment><USER17> I've always found it odd that there has been this quest for stronger and stronger cannabis.

In my experience it all costs the same. That super dank hydo that has had daily love and care sells for the same price as bush weed that was planted in a forest and then harvested a few months later.

I don't really smoke weed, but when I do I much prefer smoking spliffs (tobacco and weed, rolled into a joint). I think the French have the right idea, they smoke weed all day long and are never too high, because they are basically smoking cigarettes with a touch of green in them. Of course, it's terrible for you because you're basically smoking giant cigarettes with no filter.

<comment><USER18> > Of course, it's terrible for you because you're basically smoking giant > cigarettes with no filter.

This is a super easy thing to do, but kind of difficult to explain. I'll give it a try anyway:

Disassemble the filter of a cigarette. Split a small part of it (vertically) and fold it in half. Tear off the middle of the rolling paper's filter (about a centimeter in length). Place the small part of the cigarette filter into the middle of the rolling paper's filter, and fold the sides into a "W" shape like you usually would.

Do that once, smoke a joint, and when you're done with it, disassemble the makeshift filter you've made. Once you see how tar turned your makeshift filter almost completely black and realize all of that would end up in your lungs otherwise, you'll never roll a joint without this step.

It makes the process of rolling a bit more complicated (and almost impossible to do properly without having scissors near you), but it's totally worth the effort.

<comment><USER19> Or just buy some of these [https://www.amazon.com/Raw-Threads-Regular-Natural- Unrefined...](https://www.amazon.com/Raw-Threads-Regular-Natural- Unrefined/dp/B00AHHDF80)

Any tobacco store that sells rolling tobacco will have a variety of options available in sizes/densities/etc.

<comment><USER20> I think they give it a disgusting taste.

I rather have no filter, or much better, pipe filters. They are ceramic, paper and charcoil.

[https://www.amazon.com/Dr-Perl-Junior-Pipe- Filters/dp/B007TV...](https://www.amazon.com/Dr-Perl-Junior-Pipe- Filters/dp/B007TV2LE6)</comment></comment></comment></comment></comment></comment>


Americans don't realize state funding for higher ed is falling, new poll finds - <AUTHOR> https://hechingerreport.org/americans-think-state-funding-for-higher-ed-has-held-steady-or-risen-survey-finds/ <comment><USER2> It's crazy how fast tuition has changed for flagship state universities. I went to my states flagship just over a decade ago and paid $4500 in tuition for the entire year that was fully covered by a state scholarship that's available to every in-state high school graduate with a certain GPA.

I just looked up what this costs now. $12,000 in yearly tuition and the same scholarship that used to cover all tuition now only covers $7500 (62%). I don't think I would have been able to afford that a decade ago without taking significantly more debt (and possibly private debt) than the small amount of FAFSA loans I did take.</comment>


Companies using tests aimed at separating stars from duds - <AUTHOR> http://www.boston.com/business/articles/2010/09/12/when_hiring_employers_use_tests_to_separate_stars_from_duds/

<comment><USER2> Hmm, the balls puzzle has me stumped.

Say I pull one ball from each box, and I get two white balls and a black ball. Obviously the box that the black ball came from the box that contains all black balls.

But how can I tell which box contains all white balls, and which contains a mix of black and white balls, without pulling out a second ball?

<comment><USER3> You've missed a key piece of information: _The labels are all wrong._ Not just unreliable. _Wrong._

(P.S. You can do it in one ball.)

<comment><USER4> These puzzles are more about recognizing fuzzy areas in the problem definition than about any sort of logic. In conversational English, "the labels are all wrong" does not guarantee that each label is guaranteed wrong, only that at least one of the labels is done incorrectly.

Another example: You have a room with one light bulb. Outside the room are three switches. How do you determine which switch controls the light bulb by only opening the door once.

This problem requires you to suspend certain assumptions about the real world (you can't see light coming from underneath the door), while preserving other ones (you can hold the light bulb, and it heats up, it stays hot). Solving the problem is more about finding the right level of fuzzying the problem definition than any sort of test of logic.</comment></comment></comment>


Steve Jobs Solved the Innovator's Dilemma - <AUTHOR> http://blogs.hbr.org/cs/2011/10/steve_jobs_solved_the_innovato.html

<comment><USER2> This I think is why the general business people never seem to understand Apple.</comment>