Is it a twin paradox or a twin paradox?

Scientists Reveal the Twin Paradox! The black hole slows down time and widens the age gap between the twins!

The special theory of relativity states that the faster an object is, the slower time is.

Imagine twin brothers, one of whom steps aboard a spaceship for a long-range space trip near the speed of light, while the other stays on Earth. As a result, when the traveler returns to Earth, he should be younger than his brother who remained on Earth.

But with him as a frame of reference, the earth is also moving at close to the speed of light, so the brothers on the earth should also be younger than him.

This creates a paradox, who is young? Some argue that special relativity is wrong.

Albert Einstein famously proposed the theory of relativity, the theory that time can be changed, and soon after, a genius condemned him with the twin paradox.

Although this paradox has long been falsified.

But we can get a glimpse of genius's counterintuitive thinking.

Say that a pair of twins are born on Earth.

A child remains on earth.

At the same time, another child left Earth in a spaceship at close to the speed of light.

Who is younger among their twins?

Suppose you think that time becomes slower when you move close to the speed of light.

Well, most people would think that children who leave Earth at the speed of light are younger, but when a spaceship leaves Earth at close to the speed of light.

Of course, the answer is easy, just put the two children together and compare them, and don't tell everyone that the two children are the same young.

Then Einstein's soul would be disturbed.

The Gewinon Paradox or Getwin Fallacy is a thought experiment on the special theory of relativity. There are twin brothers, one aboard a spaceship for a long-distance space trip, while the other stays on Earth. As a result, when the traveler returns to Earth, he finds himself younger than his brother who stayed on Earth.

This result seems to contradict the special theory of relativity: each of the twins thinks that the other is moving relative to them, and therefore each thinks that the other should be younger than themselves due to the effect of time dilation. Special relativity states that all observers are equally meaningful, and that no frame of reference is preferential.

As a result, the traveler would expect to see a twin brother younger than him when he returned to Earth, but this is the opposite of what his brother thought.

But in reality the traveler's expectation is wrong: special relativity does not say that all observers have equal significance, but only observers in the inertial frame (i.e., observers who do not perform accelerated motion) have equal significance. But the spaceship undoubtedly accelerates at least once during its journey, so the Voyager is not an inertial frame.

Conversely, the brother who remained on Earth was in an inertial frame for the entire voyage (if we ignore the relatively small acceleration caused by the Earth's mass and movement), so he was able to distinguish him from his brother.

Some people who solve this paradox will think that special relativity cannot be applied to accelerating objects, but only general relativity, which is incorrect. For example, the age of the twin brothers can be accurately calculated by finding the integral of the spacetime interval in the space-time path traveled in any of their inertial frames (these paths are called worldlines). The approximation method can be used to calculate the relativity behavior of an accelerating spacecraft (see Relativity Rocket).

The only case where special relativity does not apply is when the effects of gravity cannot be ignored, and then general relativity is really needed.

This result is projected by the special theory of relativity (the phenomenon of time dilation of a moving clock) and can be verified experimentally: scientists can detect the particles produced in the upper layers of the atmosphere on the ground. If there is no time dilation, those seeds would have decayed before they reach the ground.

First of all, the twin paradox is also a completely solvable problem in special relativity, and general relativity is not required. The status of the twins is not equal. All formulas of special relativity are for two frames of inertia.

An inertial frame can be defined as follows: a frame of reference in which particles that are not subjected to force remain at rest or move in a straight line at uniform speed. If the people on Earth and the people on the spaceship can be regarded as inertial frames, then the two must never return and will never see each other again, so it is not a paradox for the two to see each other in time slowing down.

When two people meet, one of them must have gone through a process of acceleration and deceleration (such as a person on a spaceship), and in this process, you can't simply apply the clock and slow formula of special relativity (but that doesn't mean that it can't be solved by special relativity), and the final conclusion is that the person on the spaceship will be younger. Then, in general relativity, the restriction of the inertial frame is removed, and the two brothers can be discussed on an equal footing, but the conclusion is still that the one on the spaceship will be younger, and there will be no difference between the quantitative and special relativity conclusions. It's like Achilles' problem of chasing a turtle, you can have a deeper understanding of the problem by understanding the limit, but to calculate the result, you only need to learn about the problem in elementary school.

SweetyGirlssss's question: The condition for the special theory of relativity to be true is the inertial frame. The inertial frame is the starting point of the whole theory, or something like a postulate or definition, that is, it is assumed that we can find an inertial frame, and that the actual existence of an inertial frame is not the same thing (general relativity holds that there is no global inertial frame except in the absence of a gravitational field in all space).

This is like the points, lines, and planes in Euclidean geometry, and it is absolutely impossible to find objects that meet this definition exactly, but we still use Euclidean geometry. Based on the comparison of the predictions given by Maxwell's equations and relativistic mechanics with the observations, we can verify the accuracy of the frame of reference we have chosen to approximate an inertial frame. If one of the twins is good enough as an inertial frame, then the other is certainly not a good inertial frame, and this conclusion remains the same; Of course, it is also possible that neither is good, we can find a good inertial frame, such as the sun or the galactic center frame of reference, to describe the motion of these two people separately, then we can calculate exactly how old the two people were when they met, and what the result is.

In addition, to correct your statement, the one that can precisely define an inertial frame in special relativity is what I said above: a frame of reference in which an object that is not subject to force remains stationary or moves in a straight line at a uniform speed. As for the fact that gravitational forces are not able to find a particle that is not affected by force, this is one of the reasons why we need general relativity, and in fact special relativity cannot deal with gravitational problems, and you have already shown that gravity must be ignored in these problems.

The Twin Paradox: A Thought Experiment on Special Relativity.

An object with velocity, and an object with zero velocity, in an instantaneous time, is relatively meaningless, you know its velocity, but you are in any frame of reference, it is unmeasurable, however, you can't say that it has no velocity.

However, there is no absolute inertial frame, and it is impossible to precisely define an inertial frame within the framework of special relativity.

The Twin Paradox: A Thought Experiment on Special Relativity.

The twin paradox is simply explained as follows.

According to Albert Einstein, in different frames of inertia, the absolute is meaningless at the same time. It's like 3 million kilometers away, I see your clock 10 seconds slower than mine, you see my clock 10 seconds slower than yours, and if you don't believe that it takes time for light to travel, you think it's very contradictory. In the same way, in different inertial systems, the elder brother thinks that the younger brother is younger than himself, and the younger brother thinks that the younger brother is younger than himself, which is also true but not easy to understand, only when the brothers come together can they compare who is younger in the end.

The brothers, who are moving away from each other at high speed, think that the other is younger than themselves.

You can also use the theory of relativity to answer this question, and I am against it.

The more difficult twins are spaceships orbiting the Earth at the speed of light, flying at a fixed distance from the Earth, and communications can be received in a very short time. Since the relative distance is constant, then the communication time is constant, and the time is the same. That is, speed does not affect time.

The theory of relativity is to establish a four-dimensional coordinate system, and add a time coordinate system to the three-dimensional coordinate system of space. In such a coordinate system, velocity will affect time. If velocity affects time, then energy affects speed, temperature (heat energy) affects energy, and by changing the formula, then changing the temperature can also change time.

For example, AB and 2 places are 300,000 kilometers apart, and light is emitted for 1 second from A to B, and vice versa. If the light is emitted from the midpoint of AB, it will be seconds to A or B respectively, and the light will be emitted at the same time, and the time will be seconds. If the relative velocity of two lights is measured at the same time according to the theory of relativity, because the relative velocity is still c and the time is seconds, then only the AB spacing can be shortened, that is, the ruler is reduced.

The distance that should be the same has been shortened.

If the distance is not changed, the time of the light must slow down.

A key point is that in general relativity, it is the difference in gravitational potential that causes the difference in clock speed, and it is important to note that it is not caused by the difference in gravitational field strength.

The elder brother who rode the rocket explained that he was young in this way: when he did the exercise at a constant speed, he saw that his younger brother was getting younger; Although he was in a strong equivalent gravitational field at the time of departure and landing, because he was very close to his brother at that time, the gravitational potential of the two was not much different, and the difference between their clocks during these two phases can be ignored. He is also in a strong equivalent gravitational field when he turns around, and he is very far away from his brother at this time, so that the gravitational potential he is in is much lower than the gravitational potential that his brother is in, and he will see his brother grow old rapidly. Combining the various stages, the younger brother is older.

The younger brother is always in an inertial frame, and he uses the special theory of relativity without having to consider the general theory of relativity to explain the younger brother's youth.

The Twin Paradox: A Thought Experiment on Special Relativity.