My ignorance of time travel.

[saenbateman]

Click on the link and read the text.
http://yfrog.com/2otimegj

Please enlighten me.
On time travel why would block A bounce back?

Some of my friends assume with time travel things just instantaneously just disappear and reappear at the point in space to what time you're travelling to.
Even though this is all hypothetical I thought because time isn't universal but relative that even going back in time you may still have a different past, E.G. You couldn't visit yourself 10 minutes ago as the atoms that made up you ten minutes ago went into the time machine and came back with you, a new set of atoms don't just appear and make up the old you and if they did then there would be more mass in the universe and because of E=MC^2 then there is more energy a fundamental point is physics you can't create energy on;y transfer it.

 

[saenbateman]

I am by no means smart I was just thinking about this due to the grandfather paradox and was hoping you could help me.

 

[Commander Eagle]

The question doesn't make sense. Number one, why does time slow for block A because you put block B in a time machine? Number two, if block A stops, it won't be impacting block B, and so can't transfer energy in the first place. Number three, the bit about energy being lost doesn't make any sense: if block B is in a time machine, it isn't there for block A to hit in the first place, so there's nothing for it to transfer energy to. Number four, even ignoring the other three points, it's impossible to know, because we have no idea how time travel would work - and it's doubtful that it is even possible. To answer the question, we would have to know exactly how this time machine works.

This question is either poorly worded or nonsensical.

 

[saenbateman]

1) Because it's going back in time.
2) stops due to the time machine going back in time, it was a way to get you to imagine time is not just a back and forward thing it goes at different speeds.
3)I have no idea what you mean

 

[Commander Eagle]

1) Because it's going back in time.

Block B was put in the time machine. Block A wasn't.

2) stops due to the time machine going back in time, it was a way to get you to imagine time is not just a back and forward thing it goes at different speeds.

This doesn't make any sense. The objection was that, since B was put into a time machine and therefore not present, A couldn't hit B to transfer energy into it. This has nothing to do with what I said.

3)I have no idea what you mean

Block B was put into a time machine. It is, therefore, not where it should be when it should be. So Block A has nothing to run into. When it reaches the point where it was supposed to hit block B, there's no block B to hit, so it can't transfer the energy.

 

[saenbateman]

Block B was put in the time machine. Block A wasn't.

Yes and you're point?

 

[Commander Eagle]

Block B was put in the time machine. Block A wasn't.

Yes and you're point?

If block B was in the time machine, why does time slow for block A?

 

[ladiesman391]

Watch the movie "Back to the Future" it really is helpful in painting a simplistic version of what may occur if time travel were possible and you met yourself in the past or future.

What if, hypothetically, you travelled faster than the speed of light in your own body, wouldn't things then go in reverse like rewinding a movie? Instead of seeing it in normal, forward "Play" mode you would see it in "Rewind" mode, energy that is slower than the speed of light (including sound) would move in reverse as you would be sensing where the energy travelled FROM not where the energy travelled TO....

If you travelled close to, but slightly slower than the speed of light things would begin to slow down around you as you they are not travelling so quickly relative your position.

Relativity.

 

[saenbateman]

Because it's in a time machine to go back in time.

 

[ladiesman391]

Because it's in a time machine to go back in time.

Hahaha block A doesn't get put in the time machine, time does not slow down for block A, time slows down gradually for block B (as it begins travelling faster and faster) as it approaches the speed of light, once it exceeds the speed of light everything travels in reverse.. get it...

 

[Commander Eagle]

Because it's in a time machine to go back in time.

But block A is not in the time machine. From what perspective is block A's time slowing?

 

[ladiesman391]

"So what happens to block A and why?"

Block A keeps travelling along, it just keeps on rolling, as block B is not there for it to bump into it continues along maintaining it's momentum as it still holds this momentum that it would have (had block B still been there) transferred onto block B.

 

[Commander Eagle]

"So what happens to block A and why?"

Block A keeps travelling along, it just keeps on rolling, as block is not there for it to bump into it continues along maintaining it's momentum as it still holds this momentum that it would have (had block B still been there) transferred onto block B.

Yeah, that's what I figured, too, but I think the question is poorly worded. I'm pretty sure it meant to ask something other than "What would happen to block A if block B weren't there?".

 

[ladiesman391]

The question doesn't make sense. Number one, why does time slow for block A because you put block B in a time machine? Number two, if block A stops, it won't be impacting block B, and so can't transfer energy in the first place. Number three, the bit about energy being lost doesn't make any sense: if block B is in a time machine, it isn't there for block A to hit in the first place, so there's nothing for it to transfer energy to. Number four, even ignoring the other three points, it's impossible to know, because we have no idea how time travel would work - and it's doubtful that it is even possible. To answer the question, we would have to know exactly how this time machine works.

This question is either poorly worded or nonsensical.

It doesn't say in the question that time slows down FOR block A, it says block A slows down (relative to block B now approaching the speed of light).

Then when block B hits the speed of light, time STOPS (relative to block B), time does not stop for block A, block A has no idea that time has stopped, from block A's perspective everything is still travelling at the same normal speed.

Then when block B passes the speed of light, relative to block B, everything starts moving in the reverse of the way it was moving previously.

 

[Commander Eagle]

The question doesn't make sense. Number one, why does time slow for block A because you put block B in a time machine? Number two, if block A stops, it won't be impacting block B, and so can't transfer energy in the first place. Number three, the bit about energy being lost doesn't make any sense: if block B is in a time machine, it isn't there for block A to hit in the first place, so there's nothing for it to transfer energy to. Number four, even ignoring the other three points, it's impossible to know, because we have no idea how time travel would work - and it's doubtful that it is even possible. To answer the question, we would have to know exactly how this time machine works.

This question is either poorly worded or nonsensical.

It doesn't say in the question that time slows down FOR block A, it says block A slows down (relative to block B now approaching the speed of light).

Ah. My bad, then - but the question still is poorly worded. Unless it was written by a sadistic theoretical physics teacher who just wanted to torture his students. You know there's at least one of them who tried to figure it out.

 

[ladiesman391]

Yeah i understand what you mean when you say "it depends on how the time machine works"....

What really needs to be answered here is what happens the instant when you reach a speed faster than the speed of light?

Would you split into two at the point you hit a speed faster than the speed of light.... with the 2ND you (travelling faster than the speed of light) seeing the original FIRST you travel in reverse.

It's that instant you hit the one mile per hr faster than the speed of light where the question needs to be answered....

If we do split into two then according to the question the second block B would see the first block B travelling in reverse back to the position it came from. SO in that instance block B would return to the position where it was hit by block A and block A would hit into it. BUT if we don't split into two then block B would witness block A going straight through the position of where block B should have been.... get it?

 

[ladiesman391]

What really needs to be answered here is what happens the instant when you reach a speed faster than the speed of light?

Would you split into two at the point you hit a speed faster than the speed of light.... with the 2ND you (travelling faster than the speed of light) seeing the original FIRST you travel in reverse.

This is the point where you would wonder if energy is being created from nothing... not transferred.... is it possible to create a new alternate "you".... it would be like an outer body experience where you see everything happen around you in reverse. The millisecond you hit a speed faster than light you would leave your old body and be moving around in your new body witnessing your old body moving in reverse.

 

[ladiesman391]

is it possible to create a new alternate "you".... it would be like an outer body experience where you see everything happen around you in reverse. The millisecond you hit a speed faster than light you would leave your old body and be moving around in your new body witnessing your old body moving in reverse.

This also opens the question to another dimension. Would the old you be able to see the new you observing him... I don't think the old you could because the new you travels faster than the speed of light, i think you would hit another dimension so to the old you the new you would be invisible. But i'm actually unsure what would happen there... my head gets stuck at that point, i could speculate but if anyone else could elaborate that would be great...

 

[Master_Ghost_Knight]

This is what we call a badly put problem. It means that what ever was given in the problem is in itself contradictory or a non starter.
1. Why the hell does time need to get slower and slower before the event? Does it make any difference if it was normal time?
if you aregoing to say that the problem must be solved in stop time then the answer is prety simple, nothing at all happens becausefor something to happen it had to be a time where something asn't and another when it became to be meaning that there is at least a minimum of plank time for anything to happen at all.
2. If B travels back in time why the hell is the past version of B gone? If you had removed the B in the past then when the A past goes by nothing happens because B past isn't there.
3. I can't even understand if on the second go the time for A is going backwards or forwards or if the critial point should be before or after the colision had took place.

Until you can clear this details, the best answer I can give you is Not Aplicable.

If time travel were possible (even though it isn't) there wouldn't be any problem for a past version of something to stop existing the moment that something travels in time, the total sum of energy would increase in the past but it would decrease back again in the future and so the total is still zero.
It would be impossible for yourpast self to disapear because:
1. Who the hell is your past self?
2. If your past self disapeared then you don't even exist much less entered in the time machin and traveled back in time.

 

[Ozymandyus]

As others have noted it is extremely poorly worded. In any case, block A should travel the exact same path that it did originally. There should now be two copies of Block B at the time of the original collision, but the block B that is time travelling is either still on its post-being-hit-by-A trajectory OR is on some other trajectory depending on how exactly the time machine works. In any case, there is no particular reason that block B being sent back in time should have any effect on the original collision unless it is put in the path of block A, which the question gives no indication of.

So Block A should still bounce back, off the past version of block B which still exists, even though another copy of block B from the future exists somewhere as well.