# What if time was round like a circle?

I got a question what if time was round? I.E. time Started about 20 million or more years ago counted down to 0. Now once it reached 0 time reversed and we started going backwards in time but kept on advancing in our lives so once theoretically we could have another ice age polar ice caps melting throwing off the natural order causing the world to go back into an ice age which history would be repeating itself showing we really could be going back in time instead of forward. then once it gets to 20 million again it starts over. ponder that and let me know if you have somthing to add to my theory

Sounds very theoretical. I suppose it is entirly posible. Its like the concept of a closed loop universe, where space curves up on itself.

philster said:
I got a question what if time was round? I.E. time Started about 20 million or more years ago counted down to 0. Now once it reached 0 time reversed and we started going backwards in time but kept on advancing in our lives so once theoretically we could have another ice age polar ice caps melting throwing off the natural order causing the world to go back into an ice age which history would be repeating itself showing we really could be going back in time instead of forward. then once it gets to 20 million again it starts over. ponder that and let me know if you have somthing to add to my theory
The proper term is "periodic," not "round." Time flowing backwards would seem to violate the principle of entropy which states that the entropy of the universe is always increasing or remaining constant. Events going backwards means that entropy is decreasing and thus a violation of a law of physics. It doesn't mean it can't happen. I just means that if it does then we'd have to change that law.

Pete

eNathan said:
Sounds very theoretical. I suppose it is entirly posible. Its like the concept of a closed loop universe, where space curves up on itself.
You're thinking of a spatially closed universe. He's referring to a temporally closed universe. You can have one without the other.

Pete

pmb_phy said:
The proper term is "periodic," not "round." Time flowing backwards would seem to violate the principle of entropy which states that the entropy of the universe is always increasing or remaining constant. Events going backwards means that entropy is decreasing and thus a violation of a law of physics. It doesn't mean it can't happen. I just means that if it does then we'd have to change that law.

Pete

However, chances are, as Hawking argued, we wouldn't be able to observe a universe in which entropy increased--or atleast if we did we would perceive time "backwards" (therefore we'd still claim entropy increased with time)--because the process of forming knowledge in our brain of past events increases entropy as whole.

εllipse said:
However, chances are, as Hawking argued, we wouldn't be able to observe a universe in which entropy increased--or atleast if we did we would perceive time "backwards" (therefore we'd still claim entropy increased with time)--because the process of forming knowledge in our brain of past events increases entropy as whole.
If time ran backwards and it was verifiable, as it must be to belong to science, then it is therefore a violation of the principle of entropy.

So while you propose such a thing how can you bring it into science? I.e. how do you propose that we observe time running backwards and what does it mean??

Pete

Is there any law of physics that states entropy cannot decrease if time were to flow backwards? I always assumed that by entropy increasing with time, that was specific to moving forwards in time.

Alkatran
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philster said:
I got a question what if time was round? I.E. time Started about 20 million or more years ago counted down to 0. Now once it reached 0 time reversed and we started going backwards in time but kept on advancing in our lives so once theoretically we could have another ice age polar ice caps melting throwing off the natural order causing the world to go back into an ice age which history would be repeating itself showing we really could be going back in time instead of forward. then once it gets to 20 million again it starts over. ponder that and let me know if you have somthing to add to my theory

If time went backwards, we wouldn't be able to know it. We'd go backwards too. For all we know, time IS going backwards. The only evidence we have that it's 'going forward' is... our own consciousness.

pmb_phy said:
If time ran backwards and it was verifiable, as it must be to belong to science, then it is therefore a violation of the principle of entropy.

So while you propose such a thing how can you bring it into science? I.e. how do you propose that we observe time running backwards and what does it mean??

Pete

You can't observe time running backwards; that's the point. Since it takes an increase in entropy in order for us to form memories of the past, we won't ever remember something from when the universe was at a lower state of entropy. Instead, our thoughts always progress as entropy increases, and thus we move forward in time as entropy increases. Hawking proposes 3 "arrows of time": entropy, awareness, and the expansion of the universe. By argument similar to what I have stated, he proves the "arrow" of entropy and awareness must be the same (we always perceive time in the same direction that entropy increases). It may be possible to perceive time in the opposite direction of the expansion of the universe, though, but for that entropy would have to decrease as the universe expanded.

And this question really doesn't have anything to do with relativity.

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Seeing as all energy will be becoming more ordered as it converges to a point, I would have thought entroy increase and expansion are more tightly bound together. If the Universe were contracting as time move forward (into the future), and entropy decreasing, I would have thought we would remember only the future (i.e. get stupider with time) and so see time as running in the opposite direction to the expansion, and therefore see entropy increasing rather than decreasing and the Universe expanding rather than contracting - i.e. everything would be exactly the same as it is now. We would call backwards in time forwards and vice versa. In principal this could be true of our Universe.

However, cause and effect becomes very weird. In a contracting Universe, for instance, humans are created by worms, bacteria and detritus feeders for no apparent reason. Animals choose to split up with their mates because they deem them as having the best traits to have already assimilated their progeny. A glass is made from smaller pieces of glass coming together, and is destroyed by people melting it for no personal gain. Something is very wrong with this Universe.