The CPT Theorem says if you replace matter with anti-matter, reverse charge, parity, and time, you will have a universe that is a mirror image of our own. That seems reasonable on the face of it. But then it goes on to say that the laws of physics will be the same when time is reversed????
Let’s pretend you are bored surfing the internet and you decide to go outside and watch paratroopers jump out of an airplane. You are standing on solid ground. Gravity is holding you firm to the earth. It has an attractive force. You look up. You see a guy jump out of the plane. He falls, his chute opens and you watch him glide to the ground. Gravity works the same way for him as it does for you: it’s an attractive force pulling him to earth.
Now, somebody flips the switch, and time reverses. You are still standing on firm, solid ground. Gravity is still an attractive force for you. But the paratrooper guy? Well he’s now falling up! Gravity is a repulsive force for him. Gravity is no longer consistent; it has changed!
You suddenly wake up and realize you were just having a bad dream. You are in your bedroom, time is moving forward and all is well with the laws of physics. You decide to play with your magnet. There are some iron filings stuck to it and there is another iron filing flying toward it. Electromagnetism seems to work as you expect. Then someone flips the switch. Time reverses. The iron filings that were stuck to the magnet stay stuck. So far, so good--but the iron filing that was flying toward your magnet is now flying away! Electromagnetism is messed up! You can’t cure it by waking up this time. The only cure is forward time.
Conclusion: It is no accident the arrow of time goes forward. The laws of physics depend on it.
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