# Natural units - how and why

1. Dec 17, 2013

### arman.k.blog

So I have been going through a book on physics-based mathematics. I have seen the author using natural units (h = c = 1) in formulae. Why is this done? Most importantly, doesn't it mess up the true calculation? For example, take e = mc^2. If I set c = 1, it becomes e = m. So if I am given a mass and have been told to calculate the energy, it's the same as the given mass! How is this all consistent? I don't get the concept. I would be glad if someone would explain it in a simple manner. Thanks in advance!

2. Dec 17, 2013

### ShayanJ

Its not that confusing.We're just saying that,our length scale is somehow that light travels one unit of it in one unit of our time. Or alternatively our time scale is somehow that light travels one unit of our length scale in that time and then say we don't care what are those time and length scales!!!Its the same about h.
And about the formula E=m. Energy is not the same as mass here! Let's say the unit of time and length scales we chose are a and b.Then we have $E(kg a/b)=m(kg) c^2(a/b)$ its just we have c=1 in the unit a/b! and of course our unit of energy here becomes different from joule.We may also alter the unit of mass to an arbitrary one which again changes our unit of energy.

3. Dec 17, 2013

### rbj

that and the page on Planck units, maybe that can help.

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