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List of major unsolved problems in physics: - Theory of everything - Quantum gravity - Hierarchy problem - Strong CP problem - Physics beyond the standard model - Interpretation of quantum mechanics - Matter–antimatter asymmetry - Proton decay and spin crisis - Neutrino mass - Extra dimensions - Arrow of time - Problem of time - Dark matter - Dark Energy - Horizon problem - Fine tuned universe - Shape of the universe - Size of the universe - Blackhole information paradox - Origin and future of the universe
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Potential energy is defined as the energy difference between the energy of an object at a current position and the energy of the object at a reference position (generally, infinitely distant position) in a force field.
The gravitational potential energy of a combination of an object with mass M and another object with mass m separated by distance R is expressed by the following formula using the gravitational constant G.
The potential energy is zero when the distance between objects is infinite, and the negative energy increases as the distance decreases by gravity.
Because there can be no negative energy in the real space, potential energy should be considered as fictitious energy. Regarding potential energy as “energy debt” is easy to understand. Then what do objects borrow energy from? The answer is the vacuum space. Potential energy is the energy debt borrowed from “the vacuum energy bank”. An increase in the negative energy means an increase in the energy given by the vacuum space.
Therefore, the law of conservation of energy is established only when the vacuum energy is counted.
When an object is attracted to another object by gravity, a certain amount of energy is given to it from the vacuum space. Hence its energy debt increases by the amount given from the vacuum space, and its momentum energy increases then it accelerates.
On the contrary, when applying a force to an object and moving it against gravity, it returns a certain amount of energy to the vacuum space. Hence the energy debt decreases by the amount returned to the vacuum space, and its momentum energy decreases then it decelerates from the initial speed.
We say “potential energy increases” when the energy debt decreases, but we should say “potential energy decreases”.
Euler’s identity - beauty in its purest form.
Albert Einstein, Physics and Reality [General Consideration Concerning the Method of Science] (1939), in Out of My Later Years, Philosophical Library, New York, NY, 1950, pp. 59-65
Happy Birthday, Albert Einstein! Genius Scientist Turns 140 Years Old Today.
The year 1905 came to be known as Einstein’s Miracle Year. He was 26 years old, and in that year he published four papers that reshaped physics.
The first explained what’s called the photoelectric effect – one of the bases for modern-day electronics – with practical applications including television. His paper on the photoelectric effect helped pave the way for quantum mechanics by establishing that light is both a particle and a wave. For this work, Einstein was later awarded a Nobel Prize in physics.
Another 1905 paper related to Brownian motion. In it, Einstein stated that the seemingly random motion of particles in a fluid (Brownian motion) was a predictable, measurable part of the movement of atoms and molecules. This helped establish the Kinetic Molecular Theory of Heat, which says that, if you heat something, its molecules begin to vibrate. At this same time, Einstein provided definitive confirmation that atoms and molecules actually exist.
Also in 1905, Einstein published his Special Theory of Relativity. Before it, space, time and mass all seemed to be absolutes – the same for everyone. Einstein showed that different people perceive mass, space and time differently, but that these effects don’t show up until you start moving nearly at the speed of light. Then you find, for example, that time on a swiftly moving spaceship slows down, while the mass of the ship increases. According to Einstein, a spaceship traveling at the speed of light would have infinite mass, and a body of infinite mass also has infinite resistance to motion. And that’s why nothing can accelerate to a speed faster than light speed. Because of Einstein’s special relativity, light is now seen as an absolute in a universe of shifting values for space, time and matter.
The fourth 1905 paper stated that mass and energy are equivalent. You perhaps know something of this work in Einstein’s famous equation E=mc2. That equation means that energy (E) is equal to mass (m) multiplied by the speed of light © squared. Sound simple? It is, in a way. It means that matter and energy are the same thing. It’s also very profound, in part because the speed of light is a huge number. As shown by the equation, a small amount of mass can be converted into a large amount of energy … as in atomic bombs. It’s this same conversion of mass to energy, by the way, that causes stars to shine.
But Einstein didn’t stop there. As early as 1911, he’d predicted that light passing near a large mass, such as a star, would be bent. That idea led to his General Theory of Relativity in 1916.
This paper established the modern theory of gravitation and gave us the notion of curved space. Einstein showed, for example, that small masses such as planets form dimples in space-time that hardly affect the path of starlight. But big masses such as stars produce measurably curved space.
The fact that the curved space around our sun was measurable let other scientists prove Einstein’s theory. In 1919, two expeditions organized by Arthur Eddington photographed stars near the sun made visible during a solar eclipse. The displacement of these stars with respect to their true positions on the celestial sphere showed that the sun’s gravity does cause space to curve so that starlight traveling near the sun is bent from its original path. This observation confirmed Einstein’s theory, and made Einstein a household name.
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Wormholes were first theorized in 1916, though that wasn’t what they were called at the time. While reviewing another physicist’s solution to the equations in Albert Einstein’s theory of general relativity, Austrian physicist Ludwig Flamm realized another solution was possible. He described a “white hole,” a theoretical time reversal of a black hole. Entrances to both black and white holes could be connected by a space-time conduit.
In 1935, Einstein and physicist Nathan Rosen used the theory of general relativity to elaborate on the idea, proposing the existence of “bridges” through space-time. These bridges connect two different points in space-time, theoretically creating a shortcut that could reduce travel time and distance. The shortcuts came to be called Einstein-Rosen bridges, or wormholes.
Certain solutions of general relativity allow for the existence of wormholes where the mouth of each is a black hole. However, a naturally occurring black hole, formed by the collapse of a dying star, does not by itself create a wormhole.
Wormholes are consistent with the general theory of relativity, but whether wormholes actually exist remains to be seen.
A wormhole could connect extremely long distances such as a billion light years or more, short distances such as a few meters, different universes, or different points in time
For a simplified notion of a wormhole, space can be visualized as a two-dimensional (2D) surface. In this case, a wormhole would appear as a hole in that surface, lead into a 3D tube (the inside surface of a cylinder), then re-emerge at another location on the 2D surface with a hole similar to the entrance. An actual wormhole would be analogous to this, but with the spatial dimensions raised by one. For example, instead of circular holes on a 2D plane, the entry and exit points could be visualized as spheres in 3D space.
Science fiction is filled with tales of traveling through wormholes. But the reality of such travel is more complicated, and not just because we’ve yet to spot one.
The first problem is size. Primordial wormholes are predicted to exist on microscopic levels, about 10–33 centimeters. However, as the universe expands, it is possible that some may have been stretched to larger sizes.
Another problem comes from stability. The predicted Einstein-Rosen wormholes would be useless for travel because they collapse quickly.
“You would need some very exotic type of matter in order to stabilize a wormhole,” said Hsu, “and it’s not clear whether such matter exists in the universe.”
But more recent research found that a wormhole containing “exotic” matter could stay open and unchanging for longer periods of time.
Exotic matter, which should not be confused with dark matter or antimatter, contains negative energy density and a large negative pressure. Such matter has only been seen in the behavior of certain vacuum states as part of quantum field theory.
If a wormhole contained sufficient exotic matter, whether naturally occurring or artificially added, it could theoretically be used as a method of sending information or travelers through space. Unfortunately, human journeys through the space tunnels may be challenging.
Wormholes may not only connect two separate regions within the universe, they could also connect two different universes. Similarly, some scientists have conjectured that if one mouth of a wormhole is moved in a specific manner, it could allow for time travel.
Although adding exotic matter to a wormhole might stabilize it to the point that human passengers could travel safely through it, there is still the possibility that the addition of “regular” matter would be sufficient to destabilize the portal.
Today’s technology is insufficient to enlarge or stabilize wormholes, even if they could be found. However, scientists continue to explore the concept as a method of space travel with the hope that technology will eventually be able to utilize them.
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