Using black holes as their models, an international team of researchers has found that if three or more objects move around each other, history cannot be reversed.
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Historically, scientists have had to rely on statistical arguments based on increasing entropy to explain why time only moves in one direction.
Researchers believe they have demonstrated that fundamentally time cannot be turned backwards in all cases because things don’t always happen the same way in reverse.
The researchers came to this conclusion after simulating the dance of three orbiting black holes. By running the simulation in reverse, they found that time can’t be reversed in 5% of the calculations.
Find out more about these 3 simulated black holes, how they broke the symmetry of time, and how this discovery may shape our understanding of the basic laws of nature in this Elements.
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Why Does Time Go Forward Instead of Backward?
“Most of the laws of physics, like gravity and quantum mechanics, are symmetric with respect to time. That means that it doesn’t matter whether time moves forward or backwards. If time ran in reverse, all the laws of physics would work the same. That is, all the laws except one.”
How Gravity Explains Why Time Never Runs Backward
“If time’s arrow follows the increase of entropy, and if the entropy in the universe is always increasing, then it means that at some point in the past, entropy must have been low. Therein lies the puzzle: why was the universe in such a low entropy state in the first place?”
Can Time go Backward?
“t seems intuitively plausible that it can, but the concept creates a variety of paradoxes. For example, a time-reversed galaxy would be invisible to us because light would flow into it instead of out.”
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