A body traveling for infinte time

[Varun Bhardwaj]

but the universe is expanding too fast for that to happen.

Mass can neither be created nor be destroyed.
Energy can neither be created nor be destroyed.
They are conserved.
You are wrong. because ( universe is expanding = universe is shrinking )

 

[craigi]

I think that infinite of any kind does not exist in presence of time.
because if anything is changing with time than it will never reach to infinite.
it can only reach infinite if it change in zero time.
because now universe is running with time , Universe is not infinite , because it is accelerating.
But the space (in which all 3 Dimensional body with mass exist ) has infinite volume because its mass is zero.
Is that true ?
if the body travel infinite distance than it needs infinite time , but if the universe is not infinite than it will not take infinite time to come back to its initial position?

Nothing can reach infinity.

One model of the universe is infinite with expansion. You can visualise it as new space emerging in existing space.

The relationship between mass and space is a complex one, we know that there is a relationship but we don't have a full picture of it yet. It's a very active area of research. The old model is that mass exists in space and deforms it, we don't know if this is.going to hold up.

For an object to return to its initial position we would require that the geometry of the universe to be finite and closed, like a sphere but in higher dimensions. It's very difficult, or even impossible to visualise.

We would also require a limit on the expansion (or contraction) of the whole universe, which is distinct from the observable universe. If new space were to be created at a faster rate than you can traverse it then you're certainly not going back to your starting point.

The answer is we just don't know. There are too many unknowns but it is plausible.

 

[phinds]

OK...I also said "if". I was suggesting a scenario under which you could get back where you started, but I wasn't saying that our universe looks that way; I was saying it doesn't. It sounds like a disagreement, but I'm not seeing a point we disagree on.

OK, I guess this is another case of my response getting ahead of my brain (apparently not having understood the post to which I am responding). I think I may be getting old. Yeah, that's it. Getting old. That's my story and I'm sticking with it

 

[craigi]

Mass can neither be created nor be destroyed.
Energy can neither be created nor be destroyed.
They are conserved.
You are wrong. because ( universe is expanding = universe is shrinking )

The model actually introduces expansion driven by the conservation of energy, which is equivalent to mass.

Sounds like fuzzy logic to me.

-Choose a random number with infinite precision.
-Can’t be done with infinite precision so there is zero probability.
-But you do get one of them, even though there was zero probability.
-If you got the zero probability event once, you can get it an infinite number of times.
-Therefore zero probability events occur infinitely many times.

Do I have it right?

You're right that it can't be done. Quantum physics prohibits it. It's completely out of the realms of our experience, which is fortunate because the predictions in this thread vary as much as they possibly could. We need to treat it as a mathematical problem. The only way that it has any physical relevance is if at least one of the dimensions of the universe is infinite, which is exactly what we were talking about. There is an analogue between the cases of bounded with infinite precision and unbounded with finite precision. It just seems, to me at least, a little easier to talk of zero probability events in the context of the former.

 

[dauto]

Just remember than when dealing with infinite sets, events with probability measure zero are not "impossible". They can even happen twice.

And if you don't know what "measure" means in this context, your logic is likely to be wrong, with probability measure 1

No doubt. If craigi had talked about choosing a rational number instead of choosing a real number I wouldn't have been so quick in declaring the probability to be zero. The real numbers are much more dense than the rational numbers.

 

[phinds]

Mass can neither be created nor be destroyed.

Uh ... this is nonsense. have you ever heard of the atomic bomb?

( universe is expanding = universe is shrinking )

More nonsense

 

[Varun Bhardwaj]

Thanks you all for finding my mistake.

 

[A.T.]

No, it won't ever reach it. How could it? the galaxy is moving away at superluminal speeds.

Your misconception is explained here (at 1:40):

https://www.youtube.com/watch?v=XBr4GkRnY04

 

[dauto]

Your misconception is explained here (at 1:40):

https://www.youtube.com/watch?v=XBr4GkRnY04

Yeah, I saw that.

 

[stevendaryl]

Infinite time does not and cannot exist, so why bother trying making a thought experiment that begins with an impossibility?

I think that's just his way of saying: If we wait long enough.

 

[xAxis]

Quote by Bobbywhy

"Infinite time does not and cannot exist, so why bother trying making a thought experiment that begins with an impossibility?"

What do you mean? If expansion o the universe is accelerating, then time will always exist.

 

[phinds]

Quote by Bobbywhy

What do you mean? If expansion o the universe is accelerating, then time will always exist.

Yes, and what does that have to do with the statement that infinite time does not exist?

 

[Khashishi]

There's another problem with the original question. There isn't a unique way to define the same point in space at two different times. This is because velocities are relative and there is not a unique point that can be considered to be at rest. At large scales, it is possible to use the cosmological microwave background as a reference for absolute rest, but the laws of physics don't require this at all.