nothing can travel faster than the speed of light...

[QuantumPion]

The mass of an object does not increase with its speed. "Relativistic mass" does not represent the mass of the object. It is a mathematical derivation from relativistic momentum. You can't just plug in m_rel into newton's equations and come up with force or kinetic energy. You have to plug them into their relativistic counterparts. The mass of the electron doesn't increase, making it harder to accelerate. This would violate conservation of momentum. The reason why you are making this mistake is because you are mixing up reference frames. The force on the electron is not F = gamma * m * a. I can't recall what the relativistic force equation is off the top of my head. Point is, you're wrong.

 

[QuantumPion]

Oh, I found it on the link posted earlier.

Addendum: What is the relativistic version of F = ma ?

For this last section, we'll write down the relativistic version of Newton's second law, F = ma. In Newton's mechanics, this equation relates vectors F and a (hence the bold script) via the mass m of the object being accelerated, which is invariant in Newton's theory. Because m is just a number, in Newton's theory the force on a mass is always parallel to the resulting acceleration.

The corresponding equation in special relativity is a little more complicated. It turns out that the force F is not always parallel to the acceleration a! To express this fact, we need to use matrix notation. Let m be the invariant mass, v be the velocity as a column vector (whose entries are expressed as fractions of c and whose magnitude is the speed v as a fraction of c), let vt be the velocity as a row vector, and let 1 be the 3 x 3 identity matrix. Also let the Greek "gamma" be ? = (1 - v2) -1/2. Then the actual result turns out to be

F = ? m (1 + ?2 v vt) a

and

a = (1 - v vt) F / (? m)

(As an aside, there's a nice correspondence to the one dimensional case here. Just as ?2 can be written as 1 + ?2 v2, and its inverse (i.e. reciprocal) is 1 - v2, so the matrix 1 + ?2 v vt has determinant ?2, as well as inverse 1 - v vt.)

Looking at this relativistic version of F = ma, we might say that when the (invariant) mass m appears, it's accompanied by a factor of ?, so that really it is the relativistic mass that's appearing. Isn't this then, a good reason why we might want to give the notion of relativistic mass more credence? Perhaps. But notice that now the acceleration is not necessarily parallel to the force that produced it. It's not hard to see from the above equations that it's easier to accelerate a mass sideways to its motion, than it is to accelerate it in the direction of its motion. So now, if we still want to maintain some meaning for relativistic mass, then we'll have to realise that it has a directional dependence--as if the object somehow has more mass in the direction of its motion, than it has sideways. Evidently the idea of relativistic mass is becoming a little more complicated than at first we might have hoped! And this is another reason why, in the end, it's so much easier to just take the mass to be the invariant quantity m, and to put any directional information into a separate, matrix, factor.

 

[LazyGit]

Excuse the non sequitor but I reffered to wikipaedia because I noticed you refused to agree with someone's statement because they didn't provide a link rather than trying to understand what they were saying or accepting that if they've (biftheunderstudy) done a degree in Physics they might have some weight of intellect behind what they say.

There've been a number of crazy conjectures on this thread, bizarre in relation to the original post I mean. Gravitational waves in all likelihood do not exist, a friend of mine wrote a paper on this so I can only defer to his knowledge. Tachyons: they don't exist (I know as a scientist I'm not supposed to say things like that but who cares, god doesn't exist either). So it looks like I agree with you there, RossGr.

Relativistic mass does exist in as much as potential energy exists or even mass exists. In response to the previous post, it is easier to accelerate a mass in a perpendicular direction because you are thereby decelerating it in the direction it was originally travelling.

Now, OP, you threw up a very interesting question that people still can't really answer. Someone referred to electromagnetism as an analogy in that if you took away a charge then the effect would propagate at the speed of light which is of course correct. One would therefore expect the same to be true for gravity but that presupposes that gravity propagates at the speed of light but we can't presuppose that because we have no graviational force boson and so don't know how it interacts with mass except that we know gravity is a 3D result of the warping of 4D space time. I would expect that if the Sun were to disappear the warp would take time to propagate through space, presumably at some speed close to that of light. Then again, who knows what the hell would happen if the Sun disappeared or suddenly gained huge amounts of mass and collapsed to a singularity, perhaps in such extreme circumstances graviational waves would be produced.

All in all though, the result of this change would not transmit anywhere faster than the speed of light.
cheers

 

[QuantumPion]

In response to the previous post, it is easier to accelerate a mass in a perpendicular direction because you are thereby decelerating it in the direction it was originally travelling.

Please clarify this statement. Momentum is a vector. Acceleration in one direction does not affect the momentum in other directions. This would violate conservation of momentum.

 

[LazyGit]

It wouldn't violate conservation of angular momentum.

 

[Blouge]

>tachyon theory

Are you sure it is a theory? Unless there is a falsifiable prediction in connection with the idea of tachyons, then it is not really a theory.

>string theory

Please, do not label the idea of strings a "theory". There is a whole bunch of string ideas but no "string theory".

>Just because its in the math doesn't mean its physical, imaginary numbers are just a tool, they have no physical meaning in any branch of physics or otherwise

Agreed. Math is ultimately just a human tool for calculating. It doesn't help that mathematicians can't agree on which axioms to use, resulting in different maths; and when they do agree they run into incompleteness.

>>yet the argument about the mass of the spacecraft increasing as the velocity approaches the speed of light is still valid
>I guess the fact that it is a poor or even incorrect view doesn't bother you?

It's valid mathematically and intuitively. I'd much rather that the Earth be struck by two pebbles traveling at c/2 than by one traveling at c, because the one travelling at c is infinitely massive.

>Gravitational waves in all likelihood do not exist

So you are saying that self-propagating disturbances in spacetime geometry don't exist? So an observer outside the solar system wouldn't experience the arrival of periodic fluctuations in their gravitational field, correlating to Jupiter orbiting the Sun, and travelling at speed c?

>Acceleration in one direction does not affect the momentum in other directions.

Agreed, I don't see how imparting a change in one of the momentum vector's coordinates would affect the other coordinates. It would, however, alter the mass of the object, i.e. sqrt(m0^2+p^2/c^2).

>What is the relativistic version of F = ma ?

F=dp/dt is easy to remember, and is true in both classical and relativistic mechanics.

 

[MotF Bane]

Well...
I know you're discussing a theoretical situation (the sun simply vanishes), but solar objects of that magnitude cannot simply vanish. Physics and how a star ends is based around the available methods of ending, of which vanishment is not one of them. We know the expansion phase would end up devouring the Earth, and if somehow (Star Wars planetary shields or something) we survived that, a black hole would be the result of a supernova. That explosion would again be destructive, and then the black hole's gravity would draw you in.

Actually, couldn't the Sun vanishing and discussing the immediacy of the cessation of the gravitational effect be similar to the event horizon of a black hole? (Just guessing here)

Also, I saw something a few years back, wherein somebody proved the speed of light has already been shattered. Something in regards to the Big Bang, given the age of the universe and the positioning by triangulation. Since we know the age of the Big Bang, and can judge where it was by judging the angles that everything is moving outwards, we can find the center point, then it becomes a simple time-distance equation, that proved the speed exceeded that of the speed of light. Anybody else heard this, or maybe can verify it? I want to say he's the same person that argued the entire universe is one huge quantum computer.

 

[Blouge]

>but solar objects of that magnitude cannot simply vanish

Perhaps not, but two billiard balls could orbit each other, and one could be knocked away by a third, high-speed billiard ball. Then we are back to the same thought experiment and all of your concerns are dismissed.

I'm not sure, but since the sun is a considerable 8 minutes away then it's probably been shown by now that the Earth is pulled toward where the sun appears to be (8 minutes behind schedule) rather than where it actually is. An ephemeris must take this into account, right? If this is indeed true, then gravity clearly travels at the same rate as light, i.e. the speed c. Destroying the sun shouldn't be necessary for checking this

>the black hole's gravity would draw you in.

Not at all, orbiting a black hole of solar mass is not much different from orbiting the sun. It's a collapsed star, not a vacuum cleaner.

>speed of light has already been shattered. Something in regards to the Big Bang

Actually, space itself is expanding this very second, such that sufficiently far objects appear to be moving away from us at faster than the speed of light. The following is pretty far-fetched, but if you could control how space expands, you would be able to accelerate objects past the speed of light. If you had that kind of ability you could easily violate causality (affect the past). [BTW I'm a determinist but have no problem throwing away the idea of causality.]

 

[rosalintechpie]

Originally posted by: f95toli
No, gravity waves travel at the speed of light so it would NOT be instantaneous.
That is why it is hopefullyposssible to detect gravity waves; one end of the interferometer would be affected before the other.

Sagalore: A better way to think about would be to say that INFORMATION can not travel at a speed faster than c; if gravity waves were indeed instantaneous it would be possible to set up an information system that used gravity detectors and big masses; by moving mass you could transfer information faster than c to the dectors and this would be a violation of SR.

That was really informative.


http://www.massage-beauty.info/default.asp

 

[LazyGit]

Originally posted by: Blouge
>Gravitational waves in all likelihood do not exist

So you are saying that self-propagating disturbances in spacetime geometry don't exist? So an observer outside the solar system wouldn't experience the arrival of periodic fluctuations in their gravitational field, correlating to Jupiter orbiting the Sun, and travelling at speed c?

Oh yeah I forgot about the study that guy did outside the solar system to detect gravitational waves. I said that in all likelihood they don't exist. Fluctuations in gravitational force is not proof of gravitational waves, they are much more complicated than that.

Oh and if something massive appeared to destroy the Sun we would feel the effects of that as well. This is a purely hypothetical situation. Anyone who thinks it's ridiculous to try and find an answer to an impossible situation should think of Einstein's thought experiments. I'm pretty sure it's impossible for anyone to sit on a beam of light.

The Sun will not turn into a black hole, it might not even become a neutron star. A short time after the Big Bang (supposedly) there was a period known as inflation where the universe expanded at many times the speed of light. We can never manipulate space time and will never achieve 'warp speed.'
cheers

 

[QuantumPion]

Originally posted by: LazyGit
It wouldn't violate conservation of angular momentum.

I don't think you know what you are talking about. We are not talking about a rotating object.

 

[Blouge]

>Oh yeah I forgot about the study that guy did outside the solar system to detect gravitational waves.

This remark sounds sarcastic. I guess you are opposed to thought experiments.

>Anyone who thinks it's ridiculous to try and find an answer to an impossible situation should think of Einstein's thought experiments.

So now you are for thought experiments? Make up your mind please.

>We can never manipulate space time and will never achieve 'warp speed.'

Thanks for your prophetic insight. Let me add, if man was meant to fly, he would have wings. Also, 640K should be enough for anybody. BTW, I can manipulate spacetime right now by wiggling my finger. The shockwave should reach you shortly.

Let me add the following to the discussion, with the caveat that I'm no expert on relativistic quantum mechanics! In the absence of quantum GR there might not even be a clear understanding to these issues. Please correct me if I'm wrong! These following issues appear to involve superluminal (faster than light) behavior, which is synonymous with causality violation (altering the past). I think items 1, 2, and 3 may have been experimentally demonstrated.

1. Quantum tunneling:
It might be possible for something to "travel" faster than light using quantum tunneling. A particle can be measured on one side of a barrier at one instant and then at a later instance, may be measured on the opposite side of a barrier a considerable distance away. The object could "travel" faster than c.

2. Delayed choice experiment
In the famous two-slit experiment, trying to measure the momentum of a particle (e.g. with the screen attached to springs) destroys the interference pattern. You can choose at the last minute whether or not to measure momentum or position (e.g. you could fix the screen's position), causing a superluminal disturbance and altering the wave function for the particle's past. Note: I don't believe in the Copenhagen interpretation or special "measuring devices", but I think it's commonly accepted and it supports this description of superluminal influence.

3. Related to the EPR paradox
Suppose a particle disintegrates into two other particles, which travel outwards. Measuring the spin of one particle may instantly affect the spin of the distant, entangled particle. This might not be usable as communication, but it still seems to imply superluminal travel of information.

4. Black hole evaporation
A kind of quantum tunneling (item #1), particles can seep out of a black hole, even though light itself isn't fast enough to escape. I think Hawking proposed this, although it's not been experimentally demonstrated.

My opinion is that nothing (objects, influences, information) can travel faster than light. However, causality is not absolute and these things can essentially travel at the speed of light BACKWARD in time. The difference between A causes B vs. A is caused by B, huge on a macroscopic level, is not so important at the most fundamental level. The universe is 4D and is consistent; we do not have an evolving 3D universe based on cause and effect. Superluminal phenomena only appear when we fail to embrace the causality violations, or adhere to awkward dogma like Copenhagen interpretation. I think it's arrogance to insist the universe has randomness; it's easier to accept that we just have a lot of ignorance about things like wave function collapse or how a particle chooses a non-classical path. Bohm proposed a kind of QM which has no randomness and matches experiment exactly (unfortunately it's non-relativistic). For item #3 my opinion is that, in human terms, the final measurement of the particle effectively sends a signal back in time at a mundane speed to the origin of the two particles, instructing them both on which spins to finally show. In the universe's terms, there is no act of "measurement"; consistency is simply maintained without superluminal travel. #1 can be explained using anti-particles travelling backward in time at mundane speeds.

 

[LazyGit]

Stating that gravitational waves might exist because you can imagine someone outside the solar system experiencing something to do with gravity doesn't constitute a thought experiment.

If man were meant to fly, he would indeed have wings, that's why we built planes. I am unaware of anyone capable of flying. Except Keanu Reeves.

The human race is sufficiently developed and numerous to now realise what is possible and isn't possible unlike in the past where ingorance was a virtue to most people. If people choose to ignore, it's up to them as long as they don't expect me to go along with it. Again, we will never achieve "warp speed," it's a ridiculous idea to support TV shows' plotlines.

Although all those items above are very interesting phenomena, to explain them as occasions that lightspeed is broken is like looking at an eyeball and saying "that's so complicated, God must have designed it," rather than actually investigating and finding a real reason that doesn't end on an answer that is completely impossible.

Oh and I was under the impression that accelerating an object perpendicular to its velocity would constitute rotation but I guess I don't know what I'm talking about.
cheers

 

[QuantumPion]

Originally posted by: LazyGit

Originally posted by: Blouge
>Gravitational waves in all likelihood do not exist

So you are saying that self-propagating disturbances in spacetime geometry don't exist? So an observer outside the solar system wouldn't experience the arrival of periodic fluctuations in their gravitational field, correlating to Jupiter orbiting the Sun, and travelling at speed c?

Oh yeah I forgot about the study that guy did outside the solar system to detect gravitational waves. I said that in all likelihood they don't exist. Fluctuations in gravitational force is not proof of gravitational waves, they are much more complicated than that.

Oh and if something massive appeared to destroy the Sun we would feel the effects of that as well. This is a purely hypothetical situation. Anyone who thinks it's ridiculous to try and find an answer to an impossible situation should think of Einstein's thought experiments. I'm pretty sure it's impossible for anyone to sit on a beam of light.

The Sun will not turn into a black hole, it might not even become a neutron star. A short time after the Big Bang (supposedly) there was a period known as inflation where the universe expanded at many times the speed of light. We can never manipulate space time and will never achieve 'warp speed.'
cheers

Oh and by the way, you are wrong about gravitational waves. They have already been proven to exist experimentally. They haven't been directly detected on earth yet, but astronomical observations have inferred their existence in the case of high mass, closely orbiting binary star systems.

 

[Farmer]

In special relativity, the fastest signals travel at the upper limit of c (which is a major point of the special relativity theory: light travels at c in all frames). So these gravitational waves must travel at a speed less than or equal to the speed of light. The assumption that there is instant transmission of force (gravity in this case) completely disagrees with this point; this assumption is similar to the Newtonian construct of a "perfectly rigid body," where any interaction that occurs at one end will be instantaneously felt at the other; it simply cannot happen.

There is no physical process by which anything that starts at a velocity or propagation rate less than the speed of light and then somehow accelerates to exceed the speed of light, relative to any inertial frame (the opposite is also true, if a particle begins at a speed faster than light, it can never decelerate to a speed below c); (Consider the relativistic transformations for accelerations: instead of being a parabolic relation, it is a hyperbolic relation which approaches v=c asymptoticly).

I think Einstein's Relativity book is available free somewhere on the internet. And if you want to dig a bit deeper, there's a book called "Introduction to Special Relativity" by a guy named Resnick; if you've taken single variable calculus and some Newtonian mech, it is easily accessible, and extremely eye-opening. I don't know about any of the more modern postulates, but relativity is pretty much the widely accepted theory.

 

[QuantumPion]

Actually, since gravitons are massless, they travel at the speed of light (in a vacuum), just like electromagnetic waves.

 

[f95toli]

The 1993 Nobel prize in physics
http://nobelprize.org/nobel_prizes/physics/laureates/1993/press.html
Look under the sectopn "Graviational waves"

It is true that we haven't detected gravitional waved directly yet, their effect is extremely small. Up until quite recently we simply did not have the neccesary technology.
Project like LIGO use high precison interferometery and very long arms to detect them.
Future measurements scheme might even have to include quantum-non demoltion (QND) measurements. The effect is so small that unless QND is used to "beat" the Hisenberg uncertainy limit (QND is a form of "cheating", is doesn't really violate the UP) we might never be able to detect the waves on earth.

 

[Blouge]

>The human race is sufficiently developed and numerous to now realise what is possible and isn't possible unlike in the past

Wow, I'm sure no one throughout thousands of years of human history has ever had that thought before. It makes a lot of sense, lets halt all science and R&D since humanity knows everything already!! Good thing we just found the last particle recently (the axion), it's definitely the last surprise that can possibly exists in nature. And good thing we've established that 96% of the known mass in the universe is "dark matter" and "dark energy". Glad that's cleared up. And since we have demonstrated that the universe is completely controlled by Chance, our job of explaining it is so much easier! Don't worry about the fine structure constant fluctuating, it must be an experimental error. And good thing we've calculated the age of the universe (at least the visible part) with pinpoint precision, its 10 plus or minus 5 billion years, excluding the 17-billion year old stars. And with empty space's natural tendacy to expand, it's no wonder LazyGit is so big-headed!

 

[dxkj]

-The human race is sufficiently developed and numerous to now realise what is possible
-and isn't possible unlike in the past where ingorance was a virtue to most people.

Well, you just lost all credibility with me... There have been numerous points that the human civilization reached a pinnacle where it seemed, we understand so much there can't be much more to understand....

For the small percentage of time we have been focusing on space/time/physics/etc issues, look how much new information has popped up... there is SO much we don't understand, and until we understand everything you can't make blanket statements about speed and travel and light, etc.

You sound like you are saying, its not worth trying to understand things we think are impossible, because we know better than to waste our time....

 

[LazyGit]

No, I am saying that information cannot be transmitted faster than the speed of light and that is an incontravertable fact. Sorry if you don't like that.

I thought I lost all credibility with you when I stated earlier that angular momentum was conserved (which I guess you accepted I was right about).

Gravitational waves have not been detected. Just because someone won the Nobel prize for seeing something they've classified as gravitational waves doesn't prove it. After all someone received the Nobel prize for detecting the CMB ... that doesn't prove the big bang actually happened.

I said that we know what is possible and what isn't possible. The question of lightspeed is one of these things. I didn't say that we know everything. I never said we shouldn't understand why they are impossibilities. I didn't say we should stop investigating the universe either. By suggesting that the answer to those questions you posed earlier is that lightspeed can be broken is hugely unhelpful and unscientific.

Do you not understand that saying that lightspeed can be broken is the easy way out?
cheers

 

[dxkj]

Originally posted by: LazyGit
No, I am saying that information cannot be transmitted faster than the speed of light and that is an incontravertable fact. Sorry if you don't like that.

I thought I lost all credibility with you when I stated earlier that angular momentum was conserved (which I guess you accepted I was right about).

Gravitational waves have not been detected. Just because someone won the Nobel prize for seeing something they've classified as gravitational waves doesn't prove it. After all someone received the Nobel prize for detecting the CMB ... that doesn't prove the big bang actually happened.

I said that we know what is possible and what isn't possible. The question of lightspeed is one of these things. I didn't say that we know everything. I never said we shouldn't understand why they are impossibilities. I didn't say we should stop investigating the universe either. By suggesting that the answer to those questions you posed earlier is that lightspeed can be broken is hugely unhelpful and unscientific.

Do you not understand that saying that lightspeed can be broken is the easy way out?
cheers

I think saying that lightspeed CANT be broken with our limited amount of knowledge is the easy way out.

I agree that lightspeed more than likely can't be broken, but based on what we know it isn't a certain, especially with some of the earlier mentioned theories/experiments that we cant explain. There are a lot of unknowns, and hell, I know far less than you, but you look back in history and almost everytime someone said we know enough to make a declaration, they end up being proven at least partially wrong/ignorant.