Do you think time travel will ever be possible?

[cquark]

Originally posted by: jb

Originally posted by: f95toli
The problem with that idea is that you can not use entaglement (=quantum teleportation in this case) to transfer information faster than the speed of light.

i thought that it was thought of as instantaneous. i could be wrong.

Entanglement does have instantaneous effects, but not ones that can be used to transfer information.

For example, if you start with a spin 0 system and it decays into two spin 1/2 particles travelling away from each other rapidly. Sometime later when the particles are say 1km apart, you collapse the wavefunction of one of them by measuring its spin. You have a 50/50 chance for +1/2 or -1/2. Let's say that it's +1/2. The other particle, 1km away, instantantously also collapses its wavefunction and by conservation of spin, we know its spin to be -1/2.

One problem for sending information is that you have no control over whether your measurement yields +1/2 or -1/2. You can't decide what data to send, as your measurement is random. If it's not random, then the states aren't entangled, so your measurement wouldn't produce any instantaneous effects.

 

[ahurtt]

nevermind

 

[Jon855]

I doubt that it is even possible at all. Sure the space and light does bends but it has nothing to do with time at all. Time's unchangable at all. Only the matters does changes, time is not a matter.

 

[f95toli]

Originally posted by: Jon855
I doubt that it is even possible at all. Sure the space and light does bends but it has nothing to do with time at all. Time's unchangable at all. Only the matters does changes, time is not a matter.

No, in GR time is just the fourth dimension; objects with large mass do indeed "bend"
spacetime.

You can actually measure this effect even on earth, satellites in orbit are affected by the gravitational field of earth and the passage of time slows down (relative to a frame on earth).

 

[BurnItDwn]

I say no, otherwise time travelers would have probably visited us by now.

 

[cquark]

Originally posted by: BurnItDwn
I say no, otherwise time travelers would have probably visited us by now.

As I pointed out above, this argument doesn't work, because the time travel permitted by General Relativity doesn't give you a way to travel to a time before you constructed the time machine, so you wouldn't see people from the future until you build a time machine.

 

[thereaderrabbit]

I say no on scientific and religious grounds (strangely enough)-

1. Thermodynamics states that entropy of a closed system can only increase with time... Entropy is build upon random movements at a molecular level... Most particles are without memory at molecular level... Thus you must reverse a random process that has no memory of it's initial state billions of times to go back only a few seconds of time... I don't think it's feasible.

2. And now for the 'God reason'. Personally- I do believe in God and Jesus. As a scientist I believe in a Big Bang based start of the universe... I cannot fathom God letting me go back and change Jesus's time on earth nor can I fathom God letting me mess with the big bang. So I guess, what I believe is that if there is a God, it is not man.

If you want to relive the moment just get it on tape the first time

-Reader

 

[thereaderrabbit]

I still like the idea of being frozen and then later unfrozen as a way to go forward in time. If this was safe- you could arrive far off in the distant future and not have aged a day.

Still it's not what people want to imagine as time travel going forward. And that area of science is truly stuck at understanding why many smaller animals can be revived after being frozen short times, but not after long times.

-Reader

 

[pakigang]

I ain't scientist or anything but just a thought

Light and time are 2 different things. They are independant from each other. For example a light travelling from a distant star which reached us in lets say 10 years. Even if we travel faster than light and reach the star, the process of light emmitance has already been done, time doesn't wait for the light or the speed it travels at. It won't be a time travel, just travelling faster than light.

Just my puny brain.

 

[MobiusPizza]

Well what scientist claims was that if you travels a higher speed, tims slow down in your perspective (Proved with atomic clocks; See my notes). They thought if you can travel at speeds greater than speed of light, it might be possible that the earth has elapsed 10 years when you have realised you just spent 10 second on the craft.

Note: I never trusted the atomic clocks straped onto some Boeing 747 experiment where it really shows the atomic clocks measures the time slower. I have high doubt in this experiment; since not everything was controlled. We know that when matter travels they gain mass. The principle of an atomic clock is to measure the one second as the time for a casesium atom to oscillate 300000 times (forgot the actual number and magnitude). BUT, increasing mass means the oscillation is slower. Basic mechanics theory explains that. So that the atomic clock is EXPECTED to be slower. HOW did the scientists uses and develop complicated explanations like general relativity to explain that while there's an already simple explanation around? ;When they couldn't even know whether the general relativity theory was indeed 100% correct.

 

[cquark]

Originally posted by: AnnihilatorX
Well what scientist claims was that if you travels a higher speed, tims slow down in your perspective (Proved with atomic clocks; See my notes). They thought if you can travel at speeds greater than speed of light, it might be possible that the earth has elapsed 10 years when you have realised you just spent 10 second on the craft.

We also observe time dilation on a daily basis in the lab with decay times of elementary particles.

Note: I never trusted the atomic clocks straped onto some Boeing 747 experiment where it really shows the atomic clocks measures the time slower. I have high doubt in this experiment; since not everything was controlled. We know that when matter travels they gain mass. The principle of an atomic clock is to measure the one second as the time for a casesium atom to oscillate 300000 times (forgot the actual number and magnitude). BUT, increasing mass means the oscillation is slower. Basic mechanics theory explains that. So that the atomic clock is EXPECTED to be slower.

Your mass does not increase as your speed increases. While many popular accounts alter the definition of mass, they're creating a new concept called relativistic mass, which you cannot substitute into every physics equation in place of mass. They're moving some of the kinetic energy over to the mass energy term to explain special relativity in a simpler, but misleading, way.

HOW did the scientists uses and develop complicated explanations like general relativity to explain that while there's an already simple explanation around? ;When they couldn't even know whether the general relativity theory was indeed 100% correct.

GR isn't a more complex explanation of mechanics; it's a theory of gravity, and it's the most precisely verified theory of physics that exists.

 

[cquark]

Originally posted by: thereaderrabbit
I still like the idea of being frozen and then later unfrozen as a way to go forward in time. If this was safe- you could arrive far off in the distant future and not have aged a day.

Vernor Vinge's Realtime book is an excellent fictional account of such time travel and its implications.

 

[cquark]

Originally posted by: thereaderrabbit
I say no on scientific and religious grounds (strangely enough)-

1. Thermodynamics states that entropy of a closed system can only increase with time... Entropy is build upon random movements at a molecular level... Most particles are without memory at molecular level... Thus you must reverse a random process that has no memory of it's initial state billions of times to go back only a few seconds of time... I don't think it's feasible.

You don't have to reverse a process to go back in time; you have to rotate your dimensions to swap your radial and time coordinates. Applying entropy to curved spacetime is even more difficult than applying conservation of energy (see my post above for that problem.)

2. And now for the 'God reason'. Personally- I do believe in God and Jesus. As a scientist I believe in a Big Bang based start of the universe... I cannot fathom God letting me go back and change Jesus's time on earth nor can I fathom God letting me mess with the big bang. So I guess, what I believe is that if there is a God, it is not man.

The time travel permitted by General Relativity doesn't give you a way to travel to a time before you constructed the time machine, so you couldn't travel back to 1CE unless you found a 2000-year old time machine.

 

[thereaderrabbit]

Originally posted by: cquark

Originally posted by: thereaderrabbit
1. Thermodynamics states that entropy of a closed system can only increase with time... Entropy is build upon random movements at a molecular level... Most particles are without memory at molecular level... Thus you must reverse a random process that has no memory of it's initial state billions of times to go back only a few seconds of time... I don't think it's feasible.

You don't have to reverse a process to go back in time; you have to rotate your dimensions to swap your radial and time coordinates. Applying entropy to curved space-time is even more difficult than applying conservation of energy (see my post above for that problem.)

I don't buy this explanation (yet). Swapping your 'radial and time coordinates' would not seem so troublesome to me if it were not for the fact that radial coordinates are so complex (as you need three pieces of information to fully define a location of an atom and there are then an unimaginable number of these particles which make up the universe) and *most notably* there is not any reverse button for entropy on the molecular level (with few exceptions which include the field I'm studying - rheology). What I'm driving at is that any shot's you've taken my first theory seem to be oversimplifications of the physical world.

So I still see time travel (going backwards) as impossible in any practical level. I think what I need more than an argument as to why I'm wrong, is one as to why time travel is right

-Reader

 

[cquark]

Originally posted by: thereaderrabbit

Originally posted by: cquark

Originally posted by: thereaderrabbit
1. Thermodynamics states that entropy of a closed system can only increase with time... Entropy is build upon random movements at a molecular level... Most particles are without memory at molecular level... Thus you must reverse a random process that has no memory of it's initial state billions of times to go back only a few seconds of time... I don't think it's feasible.

You don't have to reverse a process to go back in time; you have to rotate your dimensions to swap your radial and time coordinates. Applying entropy to curved space-time is even more difficult than applying conservation of energy (see my post above for that problem.)

I don't buy this explanation (yet). Swapping your 'radial and time coordinates' would not seem so troublesome to me if it were not for the fact that radial coordinates are so complex (as you need three pieces of information to fully define a location of an atom and there are then an unimaginable number of these particles which make up the universe) and *most notably* there is not any reverse button for entropy on the molecular level (with few exceptions which include the field I'm studying - rheology). What I'm driving at is that any shot's you've taken my first theory seem to be oversimplifications of the physical world.

You're not changing the whole universe. You're just rotating your radial and time coordinates. No one else's coordinates are modified. We're not talking about rewinding the history of the universe, so entropy doesn't come into this in any way, even if we could define it consistently in a curved spacetime, which no physicist has been able to do yet. The universe is a four-dimensional object; all of those points in the past are still out there and available to be accessed if you have a time machine. The time traveller simply moves from one 4-point to another 4-point; nothing else is altered.

Yes, I am guilty of simplifying matters to a high degree. So are you by ignoring the differences between flat 3-dimensional space and curved 4-dimensional spacetime; however, that's an essential difference because time travel is impossible in a 3-dimensional flat space with separate flat 1-dimensional time, but is permitted in a curved 4-dimensional spacetime. That difference is also the reason why thermodynamics isn't the obstacle it would be in flat Newtonian physics.

It's true that the swapping coordinates explanation in a highly curved spacetime is a highly simplified explanation. There are a lot of details in how frames are transformed in the region of a black hole, and understanding Morris and Thorne's time travel paper requires a solid understanding of Lie algebras and nonEuclidean geometries. I've heard Kip Thorne's popular book Black Holes and Time Warps is good, but I haven't read it myself. If this post doesn't help you understand general relativistic time travel, perhaps his book would be a good place to look.

 

[DennyD]

It would create a time loop that would encompass anything and everything in the universe.
1. You build a time machine
2. You go back in time and accidentally kill your mom/dad/both before you were concieved
3. You would then never had been born
4. If you were never born, you would never have gone back in time and killed your parents
5. If you never went back in time and killed your parents, you WOULD have been born
6. If you were born, the original timeline would be in place and you would have built the machine and gone back and kill your parents.
7. See #3

And here's something to think about:
What if we're all living in someone's time travelling past?

 

[Chubs]

Originally posted by: AnnihilatorX
Well what scientist claims was that if you travels a higher speed, tims slow down in your perspective (Proved with atomic clocks; See my notes). They thought if you can travel at speeds greater than speed of light, it might be possible that the earth has elapsed 10 years when you have realised you just spent 10 second on the craft.

I don't quite understand the whole "clock proof" for time dilation. Why can't it be that the speed the clock is moving is just impacting the clock's ability to keep accurate time? Just because the tool we use to measure something is affected doesn't mean that what we're measuring is affected, does it?

 

[MobiusPizza]

Originally posted by: cquark

Originally posted by: AnnihilatorX
Well what scientist claims was that if you travels a higher speed, tims slow down in your perspective (Proved with atomic clocks; See my notes). They thought if you can travel at speeds greater than speed of light, it might be possible that the earth has elapsed 10 years when you have realised you just spent 10 second on the craft.

We also observe time dilation on a daily basis in the lab with decay times of elementary particles.

Note: I never trusted the atomic clocks straped onto some Boeing 747 experiment where it really shows the atomic clocks measures the time slower. I have high doubt in this experiment; since not everything was controlled. We know that when matter travels they gain mass. The principle of an atomic clock is to measure the one second as the time for a casesium atom to oscillate 300000 times (forgot the actual number and magnitude). BUT, increasing mass means the oscillation is slower. Basic mechanics theory explains that. So that the atomic clock is EXPECTED to be slower.

Your mass does not increase as your speed increases. While many popular accounts alter the definition of mass, they're creating a new concept called relativistic mass, which you cannot substitute into every physics equation in place of mass. They're moving some of the kinetic energy over to the mass energy term to explain special relativity in a simpler, but misleading, way.

That's not right. In particle accelerators, feeding more energy increases energy of the particle. It's kinetic energy is increased. However the increase in kinetic energy did not correspond to a equvalent increase in the speed of the paticle when it is near the speed of light. The mass of the particle is increased as a result of the increase in kinetic energy. Particles does increase their mass when they are travelling near speed of light. When you feed in more energy, the energy is converted to mass, of the form E = mc^2. So that although the kinetic energy (0.5*m*v^2) is increased, the speed v was barely increased at all while the mass m did.

At least that's what I've heard from my teachers. Particle gain mass instead of increasing speed near speed of light. I believe it because pariticle accelerators constantly feed in energy, yet the particle did not break the light barrier at all. Their mass must have increased.

Originally posted by: Velk

Originally posted by: AnnihilatorX
If time travel is possible, we should be seeing people from future by now.

And if life on other planets is possible we should already have been overrun by hostile aliens that look like elvis - what's your point ? 8)

The two points are irrelavent to each other. Aliens shares the same time frame with us. It is highly possible that they have not have technology to intersteller travel yet.
Time is different. Time is infinite and runs forever. It has 100% chance, given the universe is stable and human live long and time-travel is possible; that we would see people coming from future.

Originally posted by: cquark
Note that the time travel permitted by General Relativity doesn't permit travel to a time before you constructed the time machine, so you wouldn't see people from the future until you build a time machine.

That means two things:
1) We cannot build a time machine now since in the past no one had built one
(Or do you mean travel to future is possible?)
2) Even if we build one now we wouldn't be able to travel to the past

 

[cquark]

Originally posted by: AnnihilatorX
At least that's what I've heard from my teachers. Particle gain mass instead of increasing speed near speed of light. I believe it because pariticle accelerators constantly feed in energy, yet the particle did not break the light barrier at all. Their mass must have increased.

I've got a PhD in theoretical physics and I've worked at a particle accelerator. They don't show that the mass increased. Use the relativistic definition of momentum p = mv / sqrt(1 - v^2/c^2) and you can avoid moving the energy into the mass term.

You can use the concept of relativistic mass to explain that, but it will mislead you elsewhere, as Taylor and Wheeler point out in the classic text on relativity, Spacetime Physics:

"Ouch! The concept of `relativistic mass' is subject to misunderstanding. That's why we don't use it. First, it applies the name mass--belonging to the magnitude of a four-vector--to a very different concept, the time component of a four-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of space-time itself."

or if you want an older authority, Einstein also made the same point:

"It is not good to introduce the concept of the mass M = m/(1-v2/c2)^1/2 of a body for which no clear definition can be given. It is better to introduce no other mass than `the rest mass' m. Instead of introducing M, it is better to mention the expression for the momentum and energy of a body in motion."

 

[cquark]

Originally posted by: AnnihilatorX

Originally posted by: cquark
Note that the time travel permitted by General Relativity doesn't permit travel to a time before you constructed the time machine, so you wouldn't see people from the future until you build a time machine.

That means two things:
1) We cannot build a time machine now since in the past no one had built one
(Or do you mean travel to future is possible?)
2) Even if we build one now we wouldn't be able to travel to the past

It's closer to (2). If you built a time machine today, you couldn't travel into the past before you built it, but tomorrow you would have the ability to travel one day into the past, two days later you could travel two days, and so forth.

 

[Gannon]

Originally posted by: f95toli
I think whole idea of having an "opinion" is flawed in this case, simply because we do not have enough information. Anyone who answers this question is simply guessing.

For some reason many people tend to think of moderns physics as a form of philosophy, but it is not; it is science and a question like "is time travel possible" has a definite answer (yes or no) but we do not know enough about the universe to answer it yet.

Maybe in 20 years if e.g. string theory continues to develop.

The reason why it's considered philosophy is because it is not supported yet by experimental evidence. You need actual experimental data to get a working theory, most of string theory is certainly NOT based on evidence. It's based on speculation and conjecture

 

[f95toli]

I don't agree. The difference between science and philophy is that there is a, at least in principle, "correct" answer to questions in the former.
The fact that we do not have any data yet does not change that, as long as it is in principle possible to test the possibility of time travel (or string theory) in an experiment it is science.

This is actually an area or active research, I've seen a few papers on wormholes in respected journals (but in most cases they don't use the term wormhole in the paper); if stable (or semi-stable) wormholes do exist then it (probably) follows that time travel is possible.

However, AFAIK there is no astronomical evidence for stable wormholes yet.

 

[Velk]

Originally posted by: AnnihilatorX

Originally posted by: Velk

Originally posted by: AnnihilatorX
If time travel is possible, we should be seeing people from future by now.

And if life on other planets is possible we should already have been overrun by hostile aliens that look like elvis - what's your point ? 8)

The two points are irrelavent to each other. Aliens shares the same time frame with us. It is highly possible that they have not have technology to intersteller travel yet.
Time is different. Time is infinite and runs forever. It has 100% chance, given the universe is stable and human live long and time-travel is possible; that we would see people coming from future.

The argument that given an infinite universe, the chances of an alien race of elvis impersonators developing far more quickly than humankind, inventing faster than light travel, coming to earth and invading must be a certainty because there's an infinite number of chances for it to happen is just as absurd as your initial argument that if it's possible to invent a time machine then someone must have done it at some point in the future and decided to come here and make a spectacle of themselves for exactly the same reason.

The sum of any number of non zero probabilities, including infinity, is never 1. If you flip a coin 6 trillion times it's still possible that every single toss was tails, and if you flip it again the chance of it being tails again is still 50%.

Even given that, your rationalisation is kind of weak - time may be infinite, but the universe is not. Even if the universe lasts an infinite amount of time, the sun does not. Even if the sun lasts an infinite amount of time, the earth does not. Not that that is actually relevant given the whole argument is bogus anyway.

 

[CptFarlow]

I agree with Son of a N00b and AnnihilatorX. If time travel into the past, which I do not believe we can do, then sometime in the past or present we would have seen people from the future. Now, just as Son of a N00b stated, near-light speed traveling would slow time to the traveler. Take this for example. Astronauts who are in the space station for months at a time come back and their watches are off from before. It is because of the increase in speed that they experience. At a greater level, well, Son of a N00b explained it perfectly.

This is also my opinion. Oh and, Back to the Future was all wrong. But still a good trilogy.

 

[Stove]

Originally posted by: f95toli

This is actually an area or active research, I've seen a few papers on wormholes in respected journals (but in most cases they don't use the term wormhole in the paper); if stable (or semi-stable) wormholes do exist then it (probably) follows that time travel is possible.

However, AFAIK there is no astronomical evidence for stable wormholes yet.

Yeah seen stuff on this too- problem is most models of stable wormholes need the existence of matter with negative mass which is proving hard to come by.