The exploration of the universe is endless, and the duty of physics is to understand our origins by understanding the universe. Over the course of decades of science, great scientists have worked hard to advance physics and gain a better understanding of human existence. However, what tools do physicists use to carry out this magnificent project? Throughout history, ancient thinkers, in order to study the existence of the universe, created a series of guesses and perspectives, which are combined to form philosophy. After hundreds of years of development, philosophy slowly appeared too general and people needed a more detailed description of phenomena and things. As a result, physics has emerged to fill this gap. And theoretical physics is a branch of physics, it uses mathematical models and the tools of theoretical physics to solve problems in classical mechanics. The advancement of theoretical physics has helped physicists solve the problems that have confused them for centuries, and has had a more significant role in breakthrough of human technology.
The Re-perception of Space and Time
Ancient philosophers proposed many similar “earth-hearted” theories through guesswork and subjective thinking to describe the universe, which then slowly became a classical universe based on Newtonian mechanics. In some aspects, however, it is still incomplete. Thus, re-perception of space and time provides another solution about universe’s structure, which is established by the creation of relativity and the theory about stable speed of light.
First and foremost, the discovery of the principle of constant light speed is a great advancement of theoretical physics. To be more specific, in the 1760’s, an apple hit the head of Newton, which let him begin thinking on gravity, then discovering the gravity, leading to the creation of Newton’s theory of gravity (NASA, May 4, 2017). Based on his classical mechanics, scientists began to revive the Ether theory abandoned in the 18th century, arguing that there was an “ether” in the universe as a medium of transmission of light, and claimed that “time” was a constant amount full of space which measures every process (Hawking & Hawking, 2001). However, theoretical physics began to be inconsistent with the actual phenomenon, since light bent when scientists were measuring in different places. This was a huge blow to theoretical physics until Einstein's special theory of relativity explained this phenomenon: the speed of light in a vacuum was always constant, regardless of the state of motion of the reference system used by the observer (Einstein, 1905). After Michelson-Morley experiment was finished by physicists Michelson and Morley, this hypothesis was certified greatly. Therefore, physicists began denying the original hypothetical theoretical system of the universe, and the principle of constant light speed has become a milestone in the cognitive universe.
Secondly, the creation of relativity by Einstein provided another explanation about structure of universe. When Einstein thought about the new theoretical system of the structure of the universe, he thought that people are hit on the head by an apple could be equivalent to people and the ground rise together then touch the apple. At the same time, this equation may explain why the person standing on the ground feels the same as when he is in an accelerated container. Einstein’s premonition that acceleration was closely related to gravity, the space might not as flat as the Newtonian universe but is curved, and the equation above will be proven (Hawking & Hawking, 2001). In this way, relativity was born. Re-perception of space and time is an indispensable breakthrough in theoretical physics, and it is also a manifestation of people jumping out of existing knowledge systems and thinking about problems in new ways.
The Creation of Quantum Mechanics
It is an interesting process to study the changing attitudes of people towards science. On the last day of the nineteenth century, when the famous physicist Kelvin was talking to other physicists, he had never forecasted that the black-body model and the theory of the speed of light, which at that time seemed to be just “two dark clouds” over physics, had destroyed the original complete physics building, and created the greatest achievement in the history of physics today. In fact, the theory of light velocity leads to relativity, and the black-body model results in quantum mechanics. According to the process of quantum mechanics’ advancement, there are two representative examples: the explanation of the photoelectric effect and the uncertainty principle.
First and foremost, the photoelectric effect is a phenomenon found by German physicist Hertz in 1887. The phenomenon has troubled physicists for years, but the explanation of it also promotes theoretical physics. To be more specific, black-body is an ideal model, as it absorbs and radiates electromagnetic waves, but does not reflect them (Yang, 2017). By studying radiation of black-body, physicists Rayleigh and Jeans were established the Rayleigh-Jeans formula through classic theories of physics to explain what they have found. However, they discovered that some of the phenomena were not suitable for outcomes. How to solve this question? This confused people in many years until physicist Planck made a hypothesis: the energy carried by the vibrating charged particles is not continuous. He created black-body radiation law to explain it (E=hv). In his formula, “h” represents Planck constant, which is the first description of quantum. Although this formula interprets black-body’s radiation perfectly, Planck still doubted his formula. After that, physicist Einstein used black-body radiation law to expound photoelectric effect, affected the discovery of light’s wave-particle duality greatly (Wang, 2018). Thanks to this explanation, Einstein was nominated for a Nobel prize in physics. In this long process, the interpretation of the photoelectric effect contains the achievements of many physicists, which promotes the development of quantum mechanics.
Secondly, the uncertainty principle is also one representative instance. While Einstein was exploring the theory of relativity, the work of Austrian physicist Schrödinger and German physicist Heisenberg left him helpless (Hawking & Jackson, 1993). The famous thought experiment “Erwin Schrödinger's Cat” and uncertainty principle confused Einstein, he made a famous statement against them: “God does not play dice with the universe”. Why did Einstein disagree with quantum mechanics? According to the uncertainty principle, people cannot determine the position of a particle and its velocity at the same time (Hawking & Hawking, 2001). Therefore, the randomness of quantum mechanics is too absurd to accept. Nevertheless, the acceptance of this particular theory represents a major advance in theoretical physics, suggesting that physicists have become tolerant and receptive to the standards of the laws of physics. Thanks to this tolerance, new theoretical physics allows physicists to explore nature that is not limited to classical physics.
The photoelectric effect and uncertainty principle are just two representative examples of theoretical physics. Indeed, there are many important theories here to illustrate phenomena and interactions in quantum mechanics, and they come together to lead the breakthrough of theoretical physics.
The Effect of Theoretical Physics on People’s Lives in The Future
The study of black body radiation and light led to two of the greatest theoretical physics theories of modern times: quantum mechanics and general relativity. In the long-term development, physicists based on general relativity to re-explore the macrocosm, through quantum mechanics to study the microscopic world, to promote the great progress of physics. Nowadays, machines invented by quantum mechanics have benefited humans in real life, such as lasers, electron microscopes and nuclear magnetic resonance technologies. However, scientists and physicists still ask themselves: can theoretical physics help humans in other aspects? In fact, there have two ways that are able to influence people’s life even their future: predict the future and space-time travel.
First and foremost, predict the future is one possible way to achieve. Before German physicist Einstein has created theory of relativity, even before German physicist Hertz has discovered the photoelectric effect, French physicist Laplace had come up with a scientific hypothesis in 1814: “There is a creature that knows the exact position and momentum of each atom in the universe and can use Newton's law to show the whole process, past, and future of cosmic events”. This is called Démon de Laplace, was the first time a physicist had made a hypothesis about satisfy the conditions for predicting the future. Nevertheless, modern interpretations of quantum mechanics have led physicists to question the reason behind the Démon de Laplace. After German physicist Heisenberg finished uncertainty principle in 1927, physicists all considered that people cannot measure the speed and position of specific particles at the same time (Wang, 2018). Does this mean that Laplace's assumption is unachievable? Today's physics does not have the capacity to achieve Démon de Laplace’s level, but it is able to reach half of Laplace’s theory, this solution is called wave function (Hawking & Hawking, 2001). Wave function is used to describe the state of microscopic systems in quantum mechanics. It means although physicists cannot measure particle’s conditions of speed and position together, they have ability to use function vaguely describe these two quantities. This gives physicists hope that, perhaps in the future, physics will be able to achieve the approximate state of the “Démon de Laplace”, then vaguely predict the micro-state, the macro-world, and finally have capacity to predict the approximate future.
Secondly, under general relativity, physicists begin think that whether space-time travel is possible in large-scale universe, or in other words, does general relativity allow space-time be curved such a point that let macro-space-time shuttles can be achieved? To be more specific, after Einstein proposed the theory of relativity, time changed from the absolute amount to relative, gravity can not only bend space without affecting time (Einstein, 1905). This suggests that everyone's time is different, allowing the emergence of fictional movies’ scenes: the subjective time of pilots passing through the space-time tunnel is only a few months away, but the Earth's time has passed for years. However, this is all based on speed. In theory, Hawking argues, passengers on planes will have fewer life as they continue to travel in the opposite direction of the Earth's rotation, will increase in opposite way. Why people do not feel that? Because in one way, they do not have “continue flying”, and in other way, this effect is too small that even less than “the benefit that do not eat junk food in planes”.
Not only limited by speed, there has another theory to against time-space travel hypothesis: Time Paradox. Although this theory was first proposed in the novel, people should not ignore it. This paradox points out one possible situation: if a traveler shuttles back through time and space and kills his grandfather, will he still exist? Or more difficult, will he get caught up in this circle of time and never escape? Even though American physicist Everett offer an explanation called parallel universes, will the parallel world that the traveler shuttles back to and his own world affected by his actions? Obviously, people do not have the experience of space travel and never encounter any people from the future asking for stones (In the Avengers 4, in order to save another world in parallel universes, Captain America once again shuttled through time and space, returned the infinity stones in the older past, thus avoided everything from the start). However, some scientists suggest that whether people can achieve time-space travel by following the boundaries of the universe, just like around Earth. This is an interesting hypothesis, but it does not fit the theories. According to modern physics, physicists argue that human still do not have capacity to figure out where is center of the universe, so they are not able to determine the boundaries of the universe. Moreover, Einstein's theory of relativity predicts the fact that the universe is expanding, so that people can never orbit the universe with the help of light-speed spacecraft. On the other side, if this voyage is completed, human will be destroyed by the blue shift of the universe (sign of the contraction of the universe). Is that means people will never achieve goal of time-space travel? In fact, space-time shuttles in the micro-world are common, people might find a way to decrease their macro size, same as the ant man in Marvel movies.
Although theoretical physics is similar to philosophy or even metaphysics in some respects, it conforms to positivism because it has a framework that is proved by reality. Predict the future and space-time travel are two goals of theoretical. Although they are hard to achieve, they provide the hope to physicists to analyze this exciting world.
References:
Einstein, A. J. A. d. P. (1905). On the electrodynamics of moving bodies. 17(891), 50.
Hawking, S., & Hawking, S. W. (2001). The universe in a nutshell: Odile Jacob.
Hawking, S., & Jackson, M. (1993). A brief history of time: Dove Audio Beverly Hills.