Why is faster-than-light travel 'impossible'?

[Urwumpe]

Special relativity is wrong? The scientific community awaits your groundbreaking article.

Go to bed again, or refresh your reading skills. I never said that special relativity is wrong - since it obviously is not. It is the way how you need to apply it to produce the paradox that does not exist.

The article about the twin paradox contained paragraphs once, about the twin paradox in special and general relativity, and how it resolves.

 

[Hielor]

Go to bed again, or refresh your reading skills. I never said that special relativity is wrong - since it obviously is not. It is the way how you need to apply it to produce the paradox that does not exist.

Enlighten me, why is Einstein wrong with applying special relativity in this manner?

 

[Fizyk]

I believe there is a misunderstanding here. You were both saying essentially the same thing, except you understand the "paradox works" phrase differently - Hielor said that "paradox works" meaning that there is no contradiction, and Urwumpe took it as if it meant "there is a contradiction":

Sorry, no--the Earth provably does not experience the acceleration that the ship does. This is why the twin paradox works. If it were symmetrical, as you propose, it wouldn't make sense for one twin to have aged and one to have not.

The twin paradox does not work at all! That is the problem with it.

So, unless I'm understanding all of this wrong, you are both right, but you don't understand each other

 

[RisingFury]

You should update the Wikipedia page with your extensive knowledge, then, because it doesn't say anything about it being wrong: HTTP://en.wikipedia.org/wiki/Twin_paradox
You also might want to consider getting published with your proof that Einstein is wrong. The scientific community will be most interested.
Edit: fixed phone-added junk

Did you even read what the article says?!

In physics, the twin paradox is a thought experiment in special relativity, in which a twin makes a journey into space in a high-speed rocket and returns home to find he has aged less than his identical twin who stayed on Earth. This result appears puzzling because each twin sees the other twin as traveling, and so, according to a naive application of time dilation, each should paradoxically find the other to have aged more slowly. In fact, the result is not a paradox in the true sense, since it can be resolved within the standard framework of special relativity. The effect has been verified experimentally using measurements of precise clocks flown in airplanes[1] and satellites.

Here's why the twin paradox isn't a paradox:
If we have a gamma factor (whatever it may be), then the time experienced by the crew will be t' = t/gamma. t' < t.
The "paradox" would be created if you don't include contraction of length. You could reverse the situation; the Earth is moving and the rocket is at rest and therefore Earth should experience time slower...

The solution to this is that the distance between Earth and the point the ship is travelling to gets decreased in the reference frame of the ship: d' = d / gamma. Therefore, they travel a "shorter" path at the same velocity, which ends up having the same time t'.

 

[jimblah]

Faster than light and the expansion of the the Universe.

General Relativity permits distortions in spacetime that allow an object to move faster than light from the point of view of a distant observer. General relativity also agrees that any technique for faster-than-light travel could also be used for time travel. The expansion of the universe causes distant galaxies to recede from us faster than the speed of light,in general relativity, velocity is a local notion, so velocity calculated using comoving coordinates does not have any simple relation to velocity calculated locally. Rules that apply to relative velocities in special relativity, such as the rule that relative velocities cannot increase past the speed of light, do not apply to relative velocities in comoving coordinates, which are often described in terms of the "expansion of space" between galaxies. This expansion rate is thought to have been at its peak during the inflationary epoch thought to have occurred in a tiny fraction of the second after the Big Bang (models suggest the period would have been from around 10^36 seconds after the Big Bang to around 10^33 seconds), when the universe may have rapidly expanded by a factor of around 10^20 to 10^30.

from http://en.wikipedia.org/wiki/Faster-than-light
For more reputable sources of information you might look up Dr. Alexei V. Filippenko, Professor of Astronomy, http://astro.berkeley.edu/people/faculty/filippenko.html. He's done two TTC lecture series; one dealing with Black Holes, and a broader lecture dealing with Astronomy and Cosmology. They're intuituitive and you most likely won't have to revue any math to get a grasp on what he's discussing. I've met him. Very nice man, and he's an Alumni of Caltech I might add for all you "Big Bang Theory" enthusiasts. Speaking of which, Levar Burton guessed starred last night. How do we go about getting Dr. S. on the show?

 

[Hielor]

I am quite aware that there is no paradox and of how the scenario which is commonly being referred to as the "twin paradox" works. As far as i can tell, urwumpe is saying that the scenario isn't true and that there is no difference between the earth and the traveler, as indicated by his earlier posts...

 

[fsci123]

I think last time i checked when a spacecraft accelerates it exsperiences time dilation causing the spacecraft to gain mass as it apporaches c and also time begins to slow down so 5 seconds of acceleration on the ship takes maybe,,, 5 days
Thats why c is hard to get to using conventional meens,,,

 

[jimblah]

Twin Paradox

If I'm not mistaken the twin paradox is a reality. The exact phenomenon would occur if a black hole was nearby. For instance, if every man, woman, and child could board a a giant "space ark" and then achieve a stable orbit around said black hole. Time for humanity would transpire at a different rate relative to the earth. When we returned, the Earth's ecosysytem could possibly have healed itself; allowing us to rebuild our civilization without the use of fossil fuels, etc. A second chance, if you will. And we would't have to expend the energy to reach speeds approaching the speed of light. Correct me if I'm wrong. It may just be wild speculation.

 

[ZombiezuRFER]

If I'm not mistaken the twin paradox is a reality. The exact phenomenon would occur if a black hole was nearby. For instance, if every man, woman, and child could board a a giant "space ark" and then achieve a stable orbit around said black hole. Time for humanity would transpire at a different rate relative to the earth. When we returned, the Earth's ecosysytem could possibly have healed itself; allowing us to rebuild our civilization without the use of fossil fuels, etc. A second chance, if you will. And we would't have to expend the energy to reach speeds approaching the speed of light. Correct me if I'm wrong. It may just be wild speculation.

That would be horribly inefficient however. The healed ecosystem will likely have many new animals and plants, none of them necessarily digestible.

 

[jimblah]

More on Time dilation and the speed of light.

That would be horribly inefficient however. The healed ecosystem will likely have many new animals and plants, none of them necessarily digestible.

It would take "timing." I've seen documentaries that suggest that as little as 10,000 years would be necessary for nature to reclaim the surface of the earth. If we could "guarantee" that a mass extinction event such as an asteroid strike didn't occur, we shouldn't have to contend with anything too outlandish as evolution typically takes much longer to produce something like T-Rex. I'd be afraid of leaving someone behind only to return and have to deal with their descendants. Unfortunately the nearest black holes we're aware of are thousands of light years away, if not further (please don't make me look it up); requiring speeds close to the speed of light and a great deal of time just to reach one. It would require an extraordinary mental feat to pull off. We couldn't leave the calculations up to someone like navigator Trey in Sunshine (2007). Maybe someone like Georg Friedrich Bernhard Riemann or Johann Carl Friedrich Gauss could pull it off.

 

[ZombiezuRFER]

Perhaps one way to have FTL travel is if we can use artificial gravity. If gravitons exist, and assuming they are not their own antiparticle, that could be one solution, right?

 

[Stoat]

Being an absurd optimist, I think the light barrier will be cracked, I'd even put money on it but the bookies would write in so many caveats. In another thread i did mention that gravity acts instantaneously, and waited fro the howls of protest. it was this problem that kept Newton awake at night, and note that Einstein takes the same view. There's an e.m speed limit of c but gravity happily ignores that.

 

[Rtyh-12]

So gravity is transported by tachyons?

I also think that the light barrier will be cracked, but not in the conventional sense, rather through worm holes or other space warping device.

 

[Urwumpe]

So gravity is transported by tachyons?

Gravitons. If they exist.

Also, if I understand relativity correctly, the only absolute is the vacuum speed of light. There can't be an absolute acceleration, only relative acceleration (Otherwise, we could also detect the absolute acceleration we experience by expansion of the universe, instead of being forced to measure relative accelerations).

If you make your moving inertial frame stationary, it must be like the universe around you accelerates, while you simply feel a gravity force that accounts for the distortion of space-time around you. The universe folds around you.

 

[Hielor]

Also, if I understand relativity correctly, the only absolute is the vacuum speed of light. There can't be an absolute acceleration, only relative acceleration (Otherwise, we could also detect the absolute acceleration we experience by expansion of the universe, instead of being forced to measure relative accelerations).

If you make your moving inertial frame stationary, it must be like the universe around you accelerates, while you simply feel a gravity force that accounts for the distortion of space-time around you. The universe folds around you.

You understand incorrectly. If a frame of reference undergoes acceleration it is by definition not an inertial frame.

In the case of a vessel accelerating away from the Earth at, let's say for sake of example, 10g, its contents inside will experience that 10g as a "gravitational" force. The Earth does not experience such a 10g force, so you know for sure which object is being accelerated and which is at rest.

The bending of space-time doesn't even come into play here--this is true even for speeds far below lightspeed.

 

[Urwumpe]

Not quite correct - an inertial frame is free of proper acceleration.

Also, about reference frames in general relativity (not just inertial ones):

There is no experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating. —Douglas C. Giancoli, Physics for Scientists and Engineers with Modern Physics, p. 155.

 

[Stoat]

So gravity is transported by tachyons?

I don't know but I don't think so. Let's write the Lorentzian in terms of refractive index sqrt(1 - 1 / eta) Now we can construct negative refractive index materials.

Interesting little aside here. A few years ago I looked the "superlens" and read a very clear and simple account of how it worked on the Univ College of London web site. It all disappeared, the reason, it has huge military implications. Super stealthy bombers anyone? Of course that might just be me being paranoid.

Anyway a negative refractive index changes the sign to plus in the Lorentzian. That suggests that we could have a phase change at the speed of light. Hop into a time machine and go back to show Newton the Lorentzian. he would tell you that it's an exponential curve. it's also possible to think of the vacuum as having viscoelastic properties. Complex in all senses of the word.

I think that the "speed" of gravity is going to be a huge number but not instantaneous. My favourite guess is that; calling this speed b;
c^2 / b^2 = 1.0545E-34 a dimensionless number but you could always multiply it by 1kg.

Anyway, it's a fun game to play.

 

[Wishbone]

:facepalm:

 

[Gumok]

One real evidence about that the relativity is happening is that we can't accelerate particles in LHC to the speed of light. We measured it, we can't reach it.
Theoretically you can move faster than c if you modify quantum content of vacuum because speed of light depends only on permitivity and permeability of vacuum and those are concrete values and something is bringing it to it (vacuum really isn't empty).

 

[Jarvitä]

I think that the "speed" of gravity is going to be a huge number but not instantaneous. My favourite guess is that; calling this speed b;
c^2 / b^2 = 1.0545E-34 a dimensionless number but you could always multiply it by 1kg.

Anyway, it's a fun game to play.

But if we introduce speed "a" as the absolute speed of vacuum tachyon polarisation transmission such that [math]a=\varepsilon{}_{0}(\sqrt{b^{2}+c^{2}})[/math], this accounts for non-instantaneous gravity waveform transmission around high-distortion areas of spacetime where special relativity would otherwise not apply due to the Lorentz contraction being inconsistent with local spacetime geometry in higher dimensions.