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Einstein may have been wrong about not surpassing the speed of light? (pg. 7)
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| DJ_Science |
| quote: | Originally posted by pozz
for example, in the special theory of relativity (the one everyone is discussing), space is warped around the presence of matter. blackholes are these points in space where matter has reach infinite density and thus you have relativistic time dilation. in the General theory, one he developed later, space itself is curved and causes the effect of gravity. a reversal of terms that is, as of yet, unproven, but tremendously productive for modern physics. |
I think you are a bit confused about the development of the special and general theories of relativity. Special relativity is completely mute about the subject of gravity. It only deals with non-inertial (non-accelerating) frames of reference which excludes those in a gravitational field. At this stage it was still believed that gravity was induced by masses and no one thought it was due to curved spacetime. The general theory of relativity was developed as an extension of the special theory to non-inertial frames of reference. It was only then that the idea of warping of spacetime was introduced. The general theory is also quite well proven and so is the warping of spacetime (if you look up an effect called gravitational lensing and you will see how). |
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| DJ_Science |
Thanks. The link doesn't work but I can probably figure it out now that I know it's from Fermi lab. |
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| Prometheus Xex |
| quote: | Originally posted by Magnetonium
There is no such thing as time as its own independent variable. Because everything that has every happened or will ever happen is happening in this eternal moment. Time only exists in the context of the movement of celestial bodies and objects relative to each other. Period. How do we measure out the day? Yeah, you betcha - the movement of Earth around the Sun, and so forth, etc. etc.
TIME travel is therefore impossible.
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| quote: | Originally posted by Dr. Z
Regarding the time travel thing, Steven Hawking was talking about a train traveling near the speed of light.
Though possible it would take immense amounts of energy (on the scale of c^2) to reach these speeds; completely impossible by today's and the next millena's capabilities of the human race.
Though say we had the resources and you had this train travelling at these speeds, a girl that walks on the train would cause her frame of reference to slow down compared to the outside observer. It would look like she is walking slowly on the train and her resultant speed would still be below c. The faster she walks on the train in her frame of reference the more of a reduction in seen in her walking from the outside frame. Which is what DJ Science said.
One misconception about relativity is that it's this mysterious force in the universe that you can harness to time travel. This is not what it is. It's simply the understanding that we perceive information through photons that hit our eyes. Hence our sight is continually limited to the medium of information being locked to a fixed speed of c. This alters the way we perceive things, especially when they travel near the speed of light. |
| quote: | Originally posted by cammaxwell
Right, that was the whole point...that time would slow the closer you got to the speed of light. Sorry if I explained it wrong... |
With some of these points presented is why I keep coming back to my thinking that time traveling to the future by means of slowing down "your time" is not time travel... is only perceived as such by you and only you.
I'd like to hypothesize that the passage of time (or length of time passing) is perceived differently in different parts of the universe by potential advanced civilizations. Some of these other worlds could have time effected differently than the way we perceive it by simply being in close proximity to a much larger, more massive object in their system. Perhaps something like a more dense star, etc, but not disallowing the chance of a race somehow evolving near a black hole or something like it. I'm wondering if time itself is variable and changes depending on where you are at any fixed point of space? |
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| DJ_Science |
| quote: | Originally posted by Prometheus Xex
I'd like to hypothesize that the passage of time (or length of time passing) is perceived differently in different parts of the universe by potential advanced civilizations. Some of these other worlds could have time effected differently than the way we perceive it by simply being in close proximity to a much larger, more massive object in their system. Perhaps something like a more dense star, etc, but not disallowing the chance of a race somehow evolving near a black hole or something like it. I'm wondering if time itself is variable and changes depending on where you are at any fixed point of space? |
I think this is not far from the truth. The curvature of spacetime (including the degree to time dilation) is completely relative to the contents of spacetime in the area and there is no such thing as a fixed global coordinate system or frame of reference. This is one of the more interesting implications of GR in my opinion; that you can't separate the coordinate system from the things that are locally inside that coordinate system. |
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| cammaxwell |
| quote: | Originally posted by DJ_Science
It's fine. I just wanted to make sure you weren't saying this setup somehow gets you to faster than light. That is how I read your original post. |
Yeah, my whole point was that time will slow down the closer you get the speed of light. But reading back on my my post I wasn't making it clear because I said the train was going at the speed of light and not just close to it.
Cheers! |
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| cammaxwell |
| quote: | Originally posted by DJ_Science
I think this is not far from the truth. The curvature of spacetime (including the degree to time dilation) is completely relative to the contents of spacetime in the area and there is no such thing as a fixed global coordinate system or frame of reference. This is one of the more interesting implications of GR in my opinion; that you can't separate the coordinate system from the things that are locally inside that coordinate system. |
Since time started with the big bang, isn't time continually expanding outward as well? |
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| DJ_Science |
| It depends on the amount of "stuff" in the universe. If there is enough dark matter/energy to produce enough gravitational force then spacetime (at this level you really have to stop thinking about space and time as being two distinct objects) will eventually contract on itself. however, the best evidence we have at the moment points to an expanding universe which will not stop. Moreover, the rate of expansion is accelerating and will eventually be faster than the speed of light (which is allowed since we're talking about spacetime itself rather than matter). |
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| infinity HiGH |
| quote: | Originally posted by DJ_Science
Thanks. The link doesn't work but I can probably figure it out now that I know it's from Fermi lab. |
That's weird. I'm clicking it now and it's working.
I'll try linking it again: Click click |
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| DJ_Science |
| quote: | Originally posted by infinity HiGH
That's weird. I'm clicking it now and it's working.
I'll try linking it again: Click click |
Seems to work now for me too. That is odd. I can't imagine the university was blocking physorg |
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| pozz |
| quote: | Originally posted by DJ_Science
I think you are a bit confused about the development of the special and general theories of relativity. Special relativity is completely mute about the subject of gravity. It only deals with non-inertial (non-accelerating) frames of reference which excludes those in a gravitational field. At this stage it was still believed that gravity was induced by masses and no one thought it was due to curved spacetime. The general theory of relativity was developed as an extension of the special theory to non-inertial frames of reference. It was only then that the idea of warping of spacetime was introduced. The general theory is also quite well proven and so is the warping of spacetime (if you look up an effect called gravitational lensing and you will see how). |
:o cool.
here was my reasoning, i can't understand the equations so bear with me:
the presence of time exists in relation only to the fastest moving particle. so:
(1)if that particle's speed is constant, then we have standard against we can measure the progressive movement of matter in the universe.
(2)if that particle's speed is variable, then time itself would dilate in response to shifts, and therefore so would space.
the special theory relies on (1), so it implicitly assumes gravity as an explanation of the relative movement of bodies of matter. the general theory abandons (1) and so leaves matter behind altogether.
isn't that the difference between the special and general theory?
no? yes?
warping is allowed under both theories, but the first relies on the presence of matter, while in the second matter is an effect of the curvature of space and not primary in causing "gravitational lensing". not being in a gravitional field is the same thing as having unilateral, homeostatic presence of gravity, with equalized exchanges between bodies (so, the same assumptions as Newtonian physics). |
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| DJ_Science |
| quote: | Originally posted by pozz
here was my reasoning, i can't understand the equations so bear with me:
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No problem. Just bear with me when I give you a detailed response :).
| quote: | Originally posted by pozz
the presence of time exists in relation only to the fastest moving particle. so:
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I have a problem with this statement to begin with. There is no fastest moving particle. In fact relativity doesn't forbid you from having particles going faster than light. It simply says that it will take you an infinite amount of energy to accelerate a particle with mass to the speed of light. Therefore if you have a particle with mass that travels below the speed of light you can never accelerate it beyond the speed of light. Or so it seems, the jury is still out on this new result. Where time is coupled to speed is the rate at which it flows.
| quote: | Originally posted by pozz
(1)if that particle's speed is constant, then we have standard against we can measure the progressive movement of matter in the universe.
(2)if that particle's speed is variable, then time itself would dilate in response to shifts, and therefore so would space.
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No, in relativity you have no absolute frame of reference. There is no universal standard you can use and your measurements are all dependent on the coordinate frame you are working in. This is related to the first point where you don't have a "fastest moving particle" which sets a global coordinate frame.
| quote: | Originally posted by pozz
the special theory relies on (1), so it implicitly assumes gravity as an explanation of the relative movement of bodies of matter. the general theory abandons (1) and so leaves matter behind altogether.
isn't that the difference between the special and general theory?
no? yes?
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No, the only two postulates behind the special theory of relativity are 1) the speed of light is constant in all frames of reference and 2) the physics observed is the same for all frames of reference. that is all. Once you postulate those two things, everything else comes naturally and logically. The first postulate is demanded by maxwell's equations for electromagnetism and the second is "common sense" for lack of an easy explanation that doesn't require a huge discussion on symmetries.
General relativity is just the extension of the above to accelerating frames of reference.
| quote: | Originally posted by pozz
warping is allowed under both theories, but the first relies on the presence of matter, while in the second matter is an effect of the curvature of space and not primary in causing "gravitational lensing". not being in a gravitional field is the same thing as having unilateral, homeostatic presence of gravity, with equalized exchanges between bodies (so, the same assumptions as Newtonian physics). |
Yes warping in the general sense of the term exists in both theories but in special relativity it is just a linear contraction/dilation of space and time. In GR you develop curvature in spacetime. Think of it this way, in SR you scale the coordinate axis but never bend them. In GR you bend them. It is this bending that produces gravitational lensing. This warping causes newtonian gravitation and Newton's law is just the GR result for a small mass which is spherically symmetric. (Newtonian gravity still requires a gravitational field.) |
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| Jem_hadar |
| Fascinating !! :disbelief |
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