Time-Reversal Symmetry Explained

In summary, time-reversal symmetry refers to the ability for a physical system to behave the same way when played in reverse, and this is often demonstrated by substituting -t into an equation and obtaining the same result as the original equation.
  • #1
fricke
39
3
I completely have no idea what time-reversal mean.
Why does, by substituting -t into an equation and if the result is the same as the original equation, then the equation is said to be time-reversal symmetry?
Also, what does that 'symmetry' mean there? An even function?
 
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  • #2
fricke said:
I completely have no idea what time-reversal mean.
Why does, by substituting -t into an equation and if the result is the same as the original equation, then the equation is said to be time-reversal symmetry?
Also, what does that 'symmetry' mean there? An even function?
http://math.ucr.edu/home/baez/time/

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  • #3
fricke said:
I completely have no idea what time-reversal mean.
Why does, by substituting -t into an equation and if the result is the same as the original equation, then the equation is said to be time-reversal symmetry?
Also, what does that 'symmetry' mean there? An even function?
Time reversal symmetry means that the physical laws governing a dynamical system would be equally descriptive if that system was played in reverse. For instance, if you showed a movie of the motion of the planets in some solar system to a physicist, and then showed the same movie in reverse, it would be impossible for her/him to decide which of the movies was played forwards and which was played backwards, because both would be equally consistent with Newton's equations.
 
Last edited:

1. What is time-reversal symmetry?

Time-reversal symmetry is a fundamental concept in physics that states that the laws of physics should remain unchanged when time is reversed. This means that the behavior of a physical system should be the same whether time is moving forward or backward.

2. How does time-reversal symmetry affect our understanding of the universe?

Time-reversal symmetry is a crucial aspect of our understanding of the universe. It helps us to explain why certain physical processes behave in a particular way and allows us to make predictions about the behavior of systems in both the past and future.

3. Is time-reversal symmetry always preserved?

No, time-reversal symmetry is not always preserved. In some physical processes, the symmetry may be broken, meaning that the behavior of a system will not be the same when time is reversed. This is often observed in processes involving the weak nuclear force.

4. How is time-reversal symmetry related to entropy?

Entropy is a measure of the disorder or randomness in a system. In a system with time-reversal symmetry, the entropy should remain constant when time is reversed. However, in systems where the symmetry is broken, entropy may increase when time is reversed, making it a useful tool in determining if a process is time-reversal symmetric.

5. Can time-reversal symmetry exist in the quantum world?

Yes, time-reversal symmetry can exist in the quantum world. In quantum mechanics, time-reversal symmetry is described by the time-reversal operator, and it is an important concept in understanding quantum phenomena, such as particle interactions and the behavior of quantum systems.

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