time travel

[dejitaru]

We're all travelling through time at the rate of one second per second - but that's not what I mean.

E=mc^2

...one twin stays behind, while the other gets into a space ship and begins travelling near the speed of light. When he returned, the twin who stayed behind was much older than his brother, etc.

I say that's a bit flawed.

They'd both be travelling near c relative to one another.

Light isn't special. It's restricted by gravity, even this speed limit.

Why c? Why "the speed of light"? This may be the speed of these gravitons.
Uh huh, but why that speed?

Even still, all of the experiments ratifying this theory were performed on Earth.

Time slows for an object when moved across a gravitic field, much as an aluminum slug is slown when moved across a magnetic field.
In theory, that is. Gravity may be only residual.

By a scheme based on Einstein's famous theory, we may be able to travel great distances forward, or even backward through time.
Since it is not pactical to travel to a large body each time this travel is desired, we would need to replicate in a laboratory what is encountered when this happens.
By passing through a ring of this high gravity material, the subject


How, specifically, could we emulate gravity for this application?

-cutting this short, have other things to do-

 

[kylebisme]

i dont think the slowing of time is relitive to gravity. in the absence of gravity, and in a vacum, imagine two simple clocks wich are made by placeing a bounceing ball inside a box bouncing, from the top to the botom of the box with the same amount of kenitic energy, each bounce equals one tick. here is a rough asci reprsentation:
_
.
_

now those clocks, standing still, the ball bounces straight up and down like so:
_
|
_

however set i one of the boxes in motion relative to the other and the ball bounces like so:
_
/
_

obviosly the slanted path is a longer distance and sence balls have the same amount of kenitic energy, the clock in relative motion takes a longer time to make one tick. hence i belive you are headed down the wrong path with your belief that a large gravitaiton feild is the key element to time travel. as for your question as why the speed of light, it is more for example purposes than anything i belive. sence eninstein belived c to be a constant and maxim value it was used for the explanation, simply becuase the greater the speed the greater the efect of relitivity on the differnce in ageing of the twins. also one thing i would like to point out is that gravitons are theortical constructs, while they may actualy exist such things have yet to be proven and speculating on their speed is ventureing far into the relm of conjecture. lastly, as for how to emulate gravity, thats a hard one to say, though sence gravtation atraction is a relitive condion if you could find a way to isolate a portion space-time small enough you could concvably create a singularty out of the least massive object. granted then comes the question of how would one isolate a portion of space-time but i figured i would mention it sence you asked.

 

[Sohcan]

...one twin stays behind, while the other gets into a space ship and begins travelling near the speed of light. When he returned, the twin who stayed behind was much older than his brother, etc.

I say that's a bit flawed.

They'd both be travelling near c relative to one another.

The "twin paradox" is itself flawed. While one may think that they are both travelling at near c relative to each other, the paradox is broken when you realize that the "astronaut" changes inertial frames (since he has to accelerate/decelerate four times), whereas the stationary observer remains in a single inertial frame. If you plot a space-time diagram, it's easy to see that the astronaut ages more slowly relative to his twim brother on earth. A correct analysis doesn't use mere time dilation, but instead uses the invariant interval delta s ( (delta s / c)^2 = (delta t)^2 - (delta x / c)^2 ).

Why c? Why "the speed of light"? This may be the speed of these gravitons.
Uh huh, but why that speed?

The absolute velocity of light in a vacuum is determined by the relative fundamental strength of electric and magnetic fields, both fundamental constants of nature. Light is a self-propogating wave composed of perpendicular electric and magnetic fields; it's no surpise that its constant velocity is determined by the fundamental strengths of the respective field constants.

c is easily derivable from Maxwell's differential equations for electromagnetic fields. In fact, Maxwell and others noted this connection to electromagnetic waves and the propogation velocity; Einstein was merely the first to assert that this connection means that light must have a constant velocity in a vacuum. It turns out that c = 1 / (e0 * u0) ^ .5, where e0 (epsilon naught) is the permittivity of free space and u0 (mu naught) is the permeability of free space.

 

[dejitaru]

however set i one of the boxes in motion relative to the other and the ball bounces like so:
_
/
_

In what relative velocity? What determines the specifics of the slant?

also one thing i would like to point out is that gravitons are theortical constructs, while they may actualy exist such things have yet to be proven and speculating on their speed is ventureing far into the relm of conjecture

Exactly.

The "twin paradox" is itself flawed. While one may think that they are both travelling at near c relative to each other, the paradox is broken when you realize that the "astronaut" changes inertial frames (since he has to accelerate/decelerate four times), whereas the stationary observer remains in a single inertial frame.

They would both accelerate/decelerate relative to one another.

What of two particles isolated in theoretical laboratory conditions - moving away from one another at the speed of light with no acceleration?

They would both be be travelling only c, but an observer standing on one of the particles would see the other as moving twice that speed.

It then must be relative to something else.

 

[kylebisme]

relitve to the clock that is "at rest" that is. the angle of the slant is determined by the accleration of the clock though space-time. the faster it goes, the more the angle of the slant and therefor the slower the clock ticks.


also your comments at the end are fundementaly flawed an observer standing on one of the particles would never see another partical traveling in the other dicrection at all no mater how slow or fast as the immage would never catch up to the observer, looking directly back while traveling at the speed of light would in essence be like looking into a black hole.

 

[dejitaru]

relitve to the clock that is "at rest" that is. the angle of the slant is determined by the accleration of the clock though space-time. the faster it goes, the more the angle of the slant and therefor the slower the clock ticks.

What direction would it slant? How is this not inertial? Is there a formula for this?

also your comments at the end are fundementaly flawed an observer standing on one of the particles would never see another partical traveling in the other dicrection at all no mater how slow or fast as the immage would never catch up to the observer, looking directly back while traveling at the speed of light would in essence be like looking into a black hole.

Well, yes, I meant that only in theory.

What object is "stationary"?

 

[kylebisme]

it slants in the direction of motion, i think you guys are looking too hard at something that is very simple. there realy is not trouble with inerta because the ball will simply be stuck to the back of the box due to accleration, however the path it travels is still at a slant relitive to the clock "at rest" as it is now not only traveling up and down, but forward also. it is esentaily the same thing as if you thow something straight up in the air while rideing on a train train, the path is like this:

/\

albit more rounded of course. were as if you thow somehing straight up wile "standing still" the path is striaght up and down. as for a forumula, while it obviously could be expressed mathmaticly i dont rightly feel up to the task at the moment, my math skills are rather rusty. as for the question "What object is "stationary"?" im not sure you what you are asking in refernace to. if you mean in general, noting is realy stationary in space-time, however in relitive comparion from various subjetive viewpoints some things lack desernable motion. that is what i am refering to when i say that one clock is "at rest." sure if you take into account that the earth wich we are useing to judge the "at rest" state is acutaly is spinning in on its axis and rotating around the sun, and that the sun is traveling its own course in this expanding universe in wich we live, yes the paths is much more complex. however that does not discount the fact that the clock "in motion" will tick slower than the clock "at rest."


also, as for you meaning what you said only in theory, fair enough but i dont see where you were going with it. however it does prompt me to bring up a theory of my own. imagine two people x and y where the sum of their velosties is euqal to c. now place those two people on paths perpindicular to each other and traveling in oposite directions. each person would the veiw the other as traveling at c, and thefore would appear to be a flash of light, more specifcly clusters of photons rather than a objects of mass wich they both consider themselfs to be. now in aply this situation backwards and imagine that clusters of photons can be contious and cabable of observation. then imagine such a culster of photons traveling along side a simiar cluster of photons at aproximatly the same speed and in aporximatly the same dicrection, would not those intelegent clusters of photons assume eachother to not be clusters of photons at all but rather objects of mass?

 

[KeillRandor]

Compared to the theory of special relativity, this is what my course book in modern Physics says about the general theory of relativity (involved in the Twin paradox)

"The general theory calls for an altogether different level of mathematical sophistication, one rarely achieved by practising physicists"

So I think it's a fugile attempt to explain the Twin paradox in detail here at AT-HT forum....


"If you think you understand the theory of relativity, you have not understood it"

 

[dejitaru]

also, as for you meaning what you said only in theory, fair enough but i dont see where you were going with it.

It seems written in stone that nothing can move faster than light, yet an observer on either of these particles would see the other moving twice that..
Say these particles are planets. If this observer were to launch a particle in the direction direction he's travelling, it would be 3x that.
Time doesn't slow when approaching c. The relative time effect is an exception.
If there are no offending chunks of mass nearby, relative time is reduced.
E=mc^2 only applies on Earth.

"If you think you understand the theory of relativity, you have not understood it"

Hmm, I first heard that quoted about Schroedinger's cat.
Of course there is much to be learned (it's still a theory)

imagine two people x and y...would not those intelegent clusters of photons assume eachother to not be clusters of photons at all but rather objects of mass?

Depending on the observer, most probably (perhaps they would need training on how to identify clusters of particles, eh?).

Or maybe I don't understand the question.

 

[Sohcan]

They would both accelerate/decelerate relative to one another.

Accelerated frames are not relative. Like I said, if you do the math with the invariant interval delta s, you arrive at the correct solution. Problems using special relativity cannot be dealt symmetrically; you have to take a view of an unaccelerated system.

What of two particles isolated in theoretical laboratory conditions - moving away from one another at the speed of light with no acceleration?

They would both be be travelling only c, but an observer standing on one of the particles would see the other as moving twice that speed.

Not so...If two particles travel away from each other at near c (say, v1 and v2), and you move to the frame of reference of one of the particles, you need to use relativistic velocity transformation to find the perceived velocity of the other particle. The simple method (without diving into four-vectors) is that the transformed velocity = v2' = (v2 - v1) / (1 - v2 * v1 / c). If both particles are moving at .9c in the lab frame, the transformed velocity of particle 2 in particle 1's frame is about .9945c.

E=mc^2 only applies on Earth.

The correct relativistic equation, E = mc^2 / (1 - (v/c)^2)^.5, certainly does not apply only on earth...it is a fundamental equation important to both special relativity and relativistic quantum mechanics. Trust me on this, I have a degree in physics.

Hmm, I first heard that quoted about Schroedinger's cat.
Of course there is much to be learned (it's still a theory)

There's very little that's not a theory in physics, but quantum mechanics is not only one of the most thoroughly tested of modern physics, but is also arguably the most practical. Quantum mechanics, quantum thermodynamics, and modern solid state physics are responsible for everything from the semiconductor industry and nuclear energy to the use of (analog) soundtracks in film. There were numerous triumphs of quantum mechanics correctly predicting fundamental observables in nature, such as the extremely accurate modeling of the g spin-factor of the electron to the use of Schroedinger's equation and numerical methods to predict the energy levels and degenerate splitting of various elements and molecules.

 

[rgwalt]

You can think of the problem with the Twin Paradox this way... The person on the space ship would "feel" the acceleration and deceleration. The act of accelerating and decelerating gives the feeling of gravity (also known as "gee" force). This is easily measurable. When the person on the space ship decelerated, turned around, and accelerated back towards Earth, there would be a measureable force that the observer on Earth would not experience. This acceleration is what violates the Twin Paradox.

Ryan

 

[dejitaru]

You can think of the problem with the Twin Paradox this way... The person on the space ship would "feel" the acceleration and deceleration. The act of accelerating and decelerating gives the feeling of gravity (also known as "gee" force). This is easily measurable. When the person on the space ship decelerated, turned around, and accelerated back towards Earth, there would be a measureable force that the observer on Earth would not experience. This acceleration is what violates the Twin Paradox.

What if he were not in a rocket ship, yet accelerated by a field which simultaneously moves every molecule of the body, such that there is no locally detectable acceleration?
Why must the acceleration be relative to nothing? Why is it the acceleration itself and not the means?

 

[rgwalt]

That field would still apply a force to the astronaut that could be measured. This acceleration is what sets the astronaut apart from his/her twin on Earth.

Ryan

 

[dejitaru]

How does the universe know which object is accelerating? The acceleration is relative to what?

What if there is no acceleration?

 

[dkozloski]

Years ago Hewlett-Packard carried some Cesium beam Atomic clocks around the world to compare the accuracy to some standard clocks in other countrys. The aircraft used was a Boeing 707 which is sub-sonic. Even at that the H-P clocks were accurate and stable enough to demonstrate a time discrepancy attributable to the speeds and distances flown. This project was thoroughly outlined in an article in Scientific American magazine.

 

[ReiAyanami]

that cuz they forgot to overclock it

 

[Wolfie]

I may not sound as technical as some of you, but this caught my attn. and I have one question.
WHAT IF
Someone was in a plane, flying in the oppisite direction of time. Say to the west. And continued for a while at a high rate of speed. Would he age faster then the people that stayed behind? Or would he age slower?

Wolfie

Or did I completely oversee what you where talking about with the spaceshuttle?

 

[Sohcan]

Originally posted by: dejitaru
How does the universe know which object is accelerating? The acceleration is relative to what?

There's nothing "magical" about accelerating frames (one that is accelerating with respect to another non-accelerating reference frame). Galilean relativity and Newton's laws of motion also only apply in inertial (non-accelerating) frames: any reference frame that moves at a constant velocity with respect to an inertial frame is also an inertial frame. The classical laws of mechanics are invariant in these frames and can use the Galilean transformation to move from one reference frame to another. The mathematics is simply different when dealing with a frame that is accelerating due to an external force. If you have had high school physics, you may have seen the classic film entitled "Frames of Reference" from 1960 that demonstrates the effects of non-inertial frames on classical dynamics.

Einstein's Special Relativity starts with a similar supposition; one of his two postulates is that the laws of physics are the same in all inertial reference frames (the second postulate is the constant velocity of light in a vacuum). Just like in classical dynamics, when one is dealing with non-inertial frames (in the case of the accelerating astronaut in the twin paradox), one cannot simply use the Lorentz transformation derived from Special Relativity to determine which one of the twins is older; doing so creates the false paradox.

It is critical to realize that the astronaut changes reference frames when he slows down, turns around, and speeds up to return to Earth. If you attempt the analysis from the perspective of the astronaut, Special Relativity fails because he changes inertial frames. General Relativity, on the other hand, reformulates some of the ideas of Special Relativity so that they are invariant to accelerating frames. But while Special Relativity uses linear algebra in its formal definition, General Relativity uses some pretty complex tensor analysis to which I haven't been exposed yet (since I decided not to continue physics into graduate school, switching to computer architecture instead ).

 

[berserker]

Wolfie (and I think a few of the other ppl here):

Time distortion has nothing whatsoever to do with velocity. It has everything to do with acceleration. To answer your question, yes, if you were in a plane that accelerated continuously, time would dilate and cause you to age slower than anyone that had not experienced that acceleration. HOWEVER, the effect is very, very small until you get to about 95% of c.


And, to be precise, it is not acceleration, but GRAVITY that has the dilating effect on time. The effects of gravity are INDISTINGUISHABLE from acceleration. This is why, in testing, clocks closer to the Earth ran slower than those that were placed at a higher altitude.

 

[Sohcan]

Time distortion has nothing whatsoever to do with velocity. It has everything to do with acceleration.

Time dilation is most certainly not dependent on an acceleration. As I noted in my previous post, Special Relativity only deals with inertial (non-accelerating) frames of reference. The relativistic transformation multiplier gamma, used in Lorentz transformations and four-vector notation, is only dependent on velocity: gamma = 1 / (1 - (v/c)^2)^.5. The simplest equation for time dilation is t' = gamma * tau, where t' is the time interval in the transformed frame and tau is the proper time interval in the rest frame.

Gravity and acceleration also produce time dilation effects, but that is in the realm of General Relativity instead of Special Relativity.

 

[Chaotic42]

You might like "In search of Schrodinger's Cat". Check it out a library. It might answer some of your questions.

 

[dejitaru]

And, to be precise, it is not acceleration, but GRAVITY that has the dilating effect on time. The effects of gravity are INDISTINGUISHABLE from acceleration. This is why, in testing, clocks closer to the Earth ran slower than those that were placed at a higher altitude.

Dammit, I said that in the first post and was berated for it.

Time dilation is most certainly not dependent on an acceleration.

I agree.

Why is the effect not reversed with deceleration?

 

[DJFuji]

But as you approach the speed of light, your mass becomes infinite. Theoretically, doesnt this make traveling at speed C impossible?

dejitaru, in your first post, it sounds a LOT like you're referring to the wormhole created by a blackhole. If i understand it correctly, the black hole become a entrance to a wormhole which tears through the fabric of space-time to place you in a different location and time.

Sohcan, what is your opinion of the multiverse theory of space-time? That there are a limitless number of alternate dimensions which branch off when we try to alter the past so that we can never alter our OWN past; merely an alternate reality branched off that resembles ours. This theory seems to perfectly remedy both the grandfather paradox and the paradox of the marble's origin.
(you see a marble at 12:00. At 12:05 you decide to send it back in time 5 minutes ago. So at 12:00 you see the marble as planned. Question: where did the marble come from?)

 

[Sohcan]

Why is the effect not reversed with deceleration?

Good question....I haven't taken a formal class on general relativity, so I can't really give you an answer.

But as you approach the speed of light, your mass becomes infinite. Theoretically, doesnt this make traveling at speed C impossible?

The mass dilation is actually an old convention that no one uses anymore...it's not really accurate to say that mass becomes approaches infinitely large as velocity increases towards c. I guess it stems from E = (gamma) *mc^2 (where gamma = 1 / (1 - (v/c)^2)^.5)...evidently some thought that this meant that "effective mass" increased with velocity via (gamma) * m. It's more accurate see that the relativistic kinetic energy required to move an object at velocity v = (gamma - 1) *mc^2.

Sohcan, what is your opinion of the multiverse theory of space-time? That there are a limitless number of alternate dimensions which branch off when we try to alter the past so that we can never alter our OWN past; merely an alternate reality branched off that resembles ours.

It's hard for me to comment since multiverse theory isn't a formally developed theory, it's more of a supposition or hypothesis. Relativistic and non-relativistic quantum mechanics theory may also have seemingly "weird" conclusions, but it's all formally derivable using integral calculus and linear algebra and is still the conceptually the simplest model. More importantly emperical observations and measurements in atomic and particle physics have verified quantum mechanics for a century. In the afterword of my quantum mechanics textbook, the author briefly mentions multiverse/many worlds (among other things) as an alternate answer to the problems solved by quantum mechanics, so evidently the established physics community is considering it. But AFAIK it would be hard to develop multiverse into a formal theory, and possibly even harder to find emperical evidence to support it.

 

[Akira13]

I believe HowStuffWorks.com has an article entitled "How Time Travel Will Work." It is very interesting, and addresses the "twin paradox." It also suggests ways that natural phenomona could be used for time travel.