Time Travel: What are the Theories & Factors?

[bcrowell]

Does anyone know the best way for me to study SR, taking into account that I am a bit behind with the math?

Some good books about special relativity are (from easiest to hardest):

Takeuchi, An Illustrated Guide to Relativity
Mermin, It's About Time: Understanding Einstein's Relativity
Taylor and Wheeler, Spacetime Physics

The advantage of Takeuchi and Mermin is that they require very little background in math or physics. Their disadvantage is a total lack of connection to experiment.

 

[hanii]

does this mean that our heart rate would slow down...and all our body functions also slow down...if we were traveling at 90% of c so that our age doesn't increase compared to the person on the earth?

 

[rede96]

does this mean that our heart rate would slow down...and all our body functions also slow down...if we were traveling at 90% of c so that our age doesn't increase compared to the person on the earth?

No, not exactly. For you, wherever you are, (Called your Frame of Reference, or FoR as you might have seen posted by people.) you age at the same rate. It is only when you move relative to someone else that they will see you age slower.

The strange thing about Relativity is that you will also see them age slower too.

 

[rede96]

Some good books about special relativity are (from easiest to hardest):

Takeuchi, An Illustrated Guide to Relativity
Mermin, It's About Time: Understanding Einstein's Relativity
Taylor and Wheeler, Spacetime Physics

The advantage of Takeuchi and Mermin is that they require very little background in math or physics. Their disadvantage is a total lack of connection to experiment.

Brilliant, thanks.

 

[edgepflow]

Is the Al-Khalili book good?

Yes, in my opinion this one sticks out above the other popular books on the subject.

 

[DaveC426913]

does this mean that our heart rate would slow down...and all our body functions also slow down...if we were traveling at 90% of c so that our age doesn't increase compared to the person on the earth?

As rede96 intimates, yes and no.

Your heart rate and metabolism will be observed to be at a different rate than that of an observer moving relative to you. You experience nothing untoward.

But note: the time dilation is quite real; it is not an illusion. Time really is marching by at a different rate for the two of you.

 

[Tanelorn]

Hong Kong scientists 'show time travel is impossible'


http://news.yahoo.com/hong-kong-scientists-show-time-travel-impossible-150026913.html


Looks like the odds that any form of time travel exists are now extremely short.

 

[phinds]

Hong Kong scientists 'show time travel is impossible'


http://news.yahoo.com/hong-kong-scientists-show-time-travel-impossible-150026913.html


Looks like the odds that any form of time travel exists are now extremely short.

What does the speed of a photon have to do with the possibility of time travel?

 

[DaveC426913]

What does the speed of a photon have to do with the possibility of time travel?

Read here:
"The possibility of time travel was raised 10 years ago when scientists discovered superluminal -- or faster-than-light -- propagation of optical pulses in some specific medium, the team said.

It was later found to be a visual effect, but researchers thought it might still be possible for a single photon to exceed light speed."

It is a specific circumstance where it looked like time travel might be possible. That specific circumstance has been ruled out. It says nothing about any other possible solution to time travel.

 

[phinds]

Read here:
"The possibility of time travel was raised 10 years ago when scientists discovered superluminal -- or faster-than-light -- propagation of optical pulses in some specific medium, the team said.

It was later found to be a visual effect, but researchers thought it might still be possible for a single photon to exceed light speed."

It is a specific circumstance where it looked like time travel might be possible. That specific circumstance has been ruled out. It says nothing about any other possible solution to time travel.

Yes, I saw that statement but infered that the "ruled out" applied to ALL possible mechanisms somehow. Thanks for that clarification

 

[Tanelorn]

Well it seems like if we can't bend the rules enough for a single photon, a very tiny piece of information, then it doesn't hold much hope for real time travel with photons or anything else.

Time travel might involve having to leave and re-enter this universe entirely, but that doesn't make sense with any real Physics I know of.
This also assumes the past actually exists to be able to enter it and not a perpetual infinitesimally wide present.

 

[DaveC426913]

Well it seems like if we can't bend the rules enough for a single photon, a very tiny piece of information, then it doesn't hold much hope for real time travel with photons or anything else.

Well, that's like of like saying, if we can't bend the rules enough for a pig to fly, it doesn't hold much hope for American Airlines.

 

[Tanelorn]

lol. Well that is another way of looking at it I guess.

Another way of looking at my view is that time is more like a singularity than a dimension in which one can travel up and down. ie. Only the present ever exists because the present, which is where the 3Dimensions of space exist, is only infinitessimal width.

A similar way of looking at it is that the preset, where all the action is going on, is like the stylus playing a record. ie. narrow as a singularity. The past and future exist as potential information only, but the stylus isn't there so you can't travel there because the action of energy conversion (or music) isn't playing there yet.

A computer processing information in a large file is also similar to the above.

 

[DaveC426913]

lol. Well that is another way of looking at it I guess.

Another way of looking at my view is that time is more like a singularity than a dimension in which one can travel up and down. ie. Only the present ever exists because the present, which is where the 3Dimensions of space exist, is only infinitessimal width.

A similar way of looking at it is that the preset, where all the action is going on, is like the stylus playing a record. ie. narrow as a singularity. The past and future exist as potential information only, but the stylus isn't there so you can't travel there because the action of energy conversion (or music) isn't playing there yet.

A computer processing information in a large file is also similar to the above.

These are all examples of traveling though one spatial dimension at a constant rate through the time dimension; which is unfortunately not doing much to illuminate the issue.

 

[Tanelorn]

Dave, I think you are probably referring to the way in which time slows in a spaceship as one moves at near light speed through space?

My answer is that whilst I agree that the passage of time passes more slowly, the present time is still the only time ever being experienced inside the spaceship during the journey. So, for me, I still don't think I could describe time as being like a dimension of space that I can move forward or back, only the present ever exists and only in the present does matter and energy exist and interact. The rest is been and gone and exists only in history books and the future is yet to be.

The matter and energy of neither the future nor the past can interact in any way with the matter and energy of the present. We could today be occupying the same spatial coordinates as a supermassive black hole, but there isn't even a quantum of interaction on the matter of the present in the same location. I think we may well have all been overly influenced by H G Wells and Dr Who et al into seeing time in the wrong way.

 

[phinds]

My answer is that whilst I agree that the passage of time passes more slowly, the present time is still the only time ever being experienced inside the spaceship during the journey. So, for me, I still don't think I could describe time as being like a dimension of space that I can move forward or back, only the present ever exists and only in the present does matter and energy exist and interact. The rest is been and gone and exists only in history books and the future is yet to be.

I see your point, and it is reasonable, but it is impossible (I think) to discuss some relativistic effects without reference to time as a dimention and it is absolutely standard in physics to treat time as a dimension in the 4d existence that is space-time.

 

[DaveC426913]

So, for me, I still don't think I could describe time as being like a dimension of space that I can move forward or back,

Correct. Because it is not like that.

The key thing about a time-like dimension, as opposed to a space-like dimension, is that we are constrained to move through it only forward, and only at a fixed speed.

 

[Tanelorn]

So the basis for ever achieving true Time Travel is exceedingly weak? i.e. backwards and forwards at will and at any speed.

 

[phinds]

So the basis for ever achieving true Time Travel is exceedingly weak? i.e. backwards and forwards at will and at any speed.

I think "weak" is a very strong categorization of the basis. "Nonexistant" may not be true, but I think it would be closer to the current understanding.

 

[Cosmo Novice]

So the basis for ever achieving true Time Travel is exceedingly weak? i.e. backwards and forwards at will and at any speed.

Forward time travel - assuming the caveat that we have relatavistic travel, is entirely plausable. Future destination time could even be factored into the equation to arrive at a certain "when".

Backwards time travel is altogether different, barring CTCs, tachyons and the doctors TARDIS it is highly unlikely this is possible - you would need FTL. If we could go FTL, we could time travel but again I don't think it possible to ever achieve true FTL and I think it unlikely there is a mechanism which allows "percieved" FTL travel.

Just my two cents worth