Why is it impossible to travel in a speed higher than light? How does relativity theory found that its impossible to achieve that? That theory is based on the assumption that light its the fastest thing, isnt it?

i reallydont get these ideas, can u explain why is it impossible to travel faster than light?

i thnik it has to do with the limit of matter breakdown through energy release
cryptonite one of the hardest matter in the universe can overcome this speed
limit earth has not such element as yet

lol! cryptonite?!! isnt that from super man movies? lol
:)

That theory is based on the assumption that light its the fastest thing, isnt it?
Actually it is based on the fact, not assumption, that the light always moves with the speed of light, no matter what speed the test equipment is moving relative to the light source. The entire theory of relativity is based on that fact.
It is quite easy to show that time must be dilated and the space must be contracted in the reference frames that are moving in relation to us, if the speed of light is always the same. Atleast now it is easy, when we know about the theory.

Actually it is based on the fact, not assumption, that the light always moves with the speed of light, no matter what speed the test equipment is moving relative to the light source.
From this fact you can show that it would take an infinite amount of energy to accelerate any given mass to the speed of light. You may find the following two websites interesting.

http://en.wikipedia.org/wiki/FTL
http://www.reference.com/browse/wiki/Faster-than-light

They mention the SR basis for the "speed limit" as well as describing how GR does not rule it out. They also do a good job of describing the more philosophical causality problems associated with faster than light travel and how traveling faster than light would essentially be the same as time travel.

-Dale

Actually it is based on the fact, not assumption, that the light always moves with the speed of light, no matter what speed the test equipment is moving relative to the light source. The entire theory of relativity is based on that fact.
To be clear: it is based on the postulate that light, or a photon if you will, is measured as the same constant, c, in all inertial frames.

Also: The entire theory of relativity is based on that <s>fact</s> postulate as well as the postulate that no frame is preferred.

To be clear: it is based on the postulate that light, or a photon if you will, is measured as the same constant, c, in all inertial frames.

Also: The entire theory of relativity is based on that <s>fact</s> postulate as well as the postulate that no frame is preferred.
As long as postulate is defined as <i>a proposition that is accepted as true in order to provide a basis for logical reasoning</i>, I agree with you, but let us not make it too difficult for Kazbadan right now.

that <s>fact</s> postulate
I don't know if you can really justify this. The speed of light frame independence has been verified by an overwhelming number of measurements. A postulate is generally something accepted without proof. With the amount of empirical evidence existing, I think that the speed of light does not qualify. (unless you are thinking of some definition of postulate that excludes empirical evidence and requires purely logical proof).

I will conceed the "no prefered frames" as a postulate.

-Dale

That kind of differences is no important. What matters is; Einsteins was lucky by guessing that the light is always travelling at the same speed no matter what speed the measurment equipment is travelling. So, that was a guess that was veirfied.

Do u think that its possible to travel faster than light? I dont know why (and this is just a feeling!) i think that something is wrong here. Maybe is possible to travel faster than light. Maybe 300000 km/sec is not the limit.


thanks for the links, i will check out now.

Maybe is possible to travel faster than light.
Maybe. I don't think GR says it is impossible, but my knowledge is limited.

But according to relativity you definitely will not ever be able to accelerate to speeds > c. If you go faster than c you will have to get there w/o accelerating somehow (e.g. wormholes etc.).

-Dale

What matters is; Einstein was lucky by guessing that the light is always travelling at the same speed no matter what speed the measurment equipment is travelling. So, that was a guess that was veirfied.
Actually it was not just a "lucky guess". Experiments that showed the fact that lights speed is always measured the same were done before. Einstein was the one who used all the experimental data and constructed a theory based on that.


Maybe is possible to travel faster than light. Maybe 300000 km/sec is not the limit.
I'm not saying you are wrong or right, but moving faster then light would violate the law of conservation of energy, because the intermediaries of interactions between matter move with the speed of light. This would also prove our current understanding of causality wrong.
Ofcourse, you can never know..

I just want to poke my head in here and stir stuff up.

I think it is best to say "nothing can move through space faster than light" because I believe situations like our expanding universe, and ergospheres around black holes permit superluminal speeds. I believe you can add the speed of space and the speed of something moving through space with simple Galilean relativity.

moreover, if you consider barrier tunneling, and similar processes, you might say that something can get from point A to point B before light can. but again, this is due to strange quantum effects where the particle may not be traveling through space (if that makes any sense).]

correct me if I am wrong anywhere.

I was thinking: can we say that is impossible to travel than light because of quantum limits? i mean, the most little measurable unit that can exist is the quantum (spacial and time). So, its impossible to travel faster than light because the light speed cross one spacial quantum in one time quantum (my english with techical stuff is even worst, so i dont see if you get my idea). There is no unit of time more little that a time-quantum neither a spacial unit (like meters, etc) more little than a spacial quantum. So, crossing a spacial-quantum in one time-quantum is the limit, ie, the speed of light.

DO you see what i mean? Can we put things on that way? btw, dont start flamimg because i dont understand a s*** of physics. :)

Yes, basically we can put it that way. Although the same logic was used in constructing the quantum limits in the first place, I think.

"Originally Posted by Aer
that <del>fact</del> postulate"

I don't know if you can really justify this. The speed of light frame independence has been verified by an overwhelming number of measurements. A postulate is generally something accepted without proof. With the amount of empirical evidence existing, I think that the speed of light does not qualify. (unless you are thinking of some definition of postulate that excludes empirical evidence and requires purely logical proof).

Pick up any undergraduate physics text that discusses special relativity. Special relativity follows from two postulates: The speed of light is the same to all observers and the laws of physics are the same in all inertial reference frames.

The speed of light has been observed to be the same for all the reference frames in which we can measure it. Those observations do not make this a universal fact. The postulate is necessary.


Original posted by kazbadan
I was thinking: can we say that is impossible to travel than light because of quantum limits?

No, you can't say that (yet). Relativity is basically a classical physics theory. Connecting relativity and quantum theory is the one of the biggest unsolved problem in physics.


Relativity theory says an object with mass cannot go exactly the speed of light. It does not say the object cannot exceed the speed of light. All we need is an infinite acceleration engine! One could then instantaneously go from a subluminal velocity to superluminal velocity without having to pass through the forbidden velocity v=c.

It's almost time for lunch and I know you don't to make me wait, so I'll defer to you and make this brief. One strong argument against travel faster than light is that there have been countless experiments in particle accelerators and none have been announced to even get a particle to c, much less over it. :(

No, you can't say that (yet). Relativity is basically a classical physics theory. Connecting relativity and quantum theory is the one of the biggest unsolved problem in physics.

No, Connecting SR with quantum theory is known as quantum field theory. QED for example is done within the framework of SR and is the most accurate theory today.

Relativity theory says an object with mass cannot go exactly the speed of light. It does not say the object cannot exceed the speed of light. All we need is an infinite acceleration engine! One could then instantaneously go from a subluminal velocity to superluminal velocity without having to pass through the forbidden velocity v=c.

I prefer cato's way of putting it. I wonder if you were to go through space at v>c (with some infinite acceleration to jump over c) if you would have to continually pump energy in to overcome losses from Cerenkov radiation. What do y'all think?

-Dale

Going through space very, very fast will bring you face to face with a lot of very, very relatively high energy gamma photons, electrons, protons, hydrogen atoms, dust motes, and so on. "Aerodynamic" drag would be prodigeous. And, kinetic energy transfer into the moving body would be spectacular. Forbidden velocity is not the only problematical thing to have to pass through. "Sorry, Charlie.". :(

An interesting thought DaleSpam. Let's suppose for a moment all the usual results are true, then a charged particle having speed v > 1 would have pure imaginary (and negative) energy. Naively we might expect it to emit Cerenkov radiation (what does it polarize? maybe the vacuum?) since it is moving faster than light. Does the radiation emitted have real energy? If it did then E would no longer be pure imaginary but actually complex because of conservation of energy. In general, a complex E means a complex v which makes just about zero sense (a little less sense even than a complex E makes ;) ). So maybe the radiation emitted would have imaginary energy and thus imaginary frequency. Imaginary frequency either means exponential damping or growth. For outgoing waves, the phase is something like exp[ikr-iwt] so w would need to be negative imaginary to make the wave decay (we don't see an universe full of infinite amounts of radiation!). This part is a bit sketchy since k needs to be imaginary too, perhaps we should choose the solution of k^2 = w^2 that makes k positve imaginary so it gives a decay too. This seems to suggest that the particle will gain energy - w, a positive imaginary quantity. The energy is therefore increased on the imaginary axis (closer to zero, goes upward) but this corresponds to increasing the speed! So the particle emits radiation that can't get much of anywhere and reaches infinite velocities. Very weird. Any thoughts on this silliness? Maybe you need a particle that always lives above v = 1 and has imaginary mass.

"The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies. However, in general relativity, velocity is a local notion, so velocity calculated using comoving coordinates does not have any simple relation to velocity calculated locally." (Reference.com)
So according to this if we traveled to a distent galaxy, and waited long enough, we would be travelling away from Earth faster then light?

Yes.

This part is a bit sketchy
Hehe, as opposed to the rest :p

I really like this. I mean, I deal with imaginary frequencies, currents, etc. all the time. So imaginary mass and energy do not bother me too much. However, if this idea is correct it would explain why such particles are not detected. Any of these particles would pull imaginary energy from the universe in order to accelerate their imaginary mass to infinite velocity thus leaving the universe before they could be detected.

If we assume that there were prodigious quantities of this imaginary mass after the big bang, it is long gone now, so we will have to create more of it in the lab in order to study it.

By the way, is there any theory on what caused the "inflationary period"?

-Dale

There are lots of ideas about the cause of the inflationary period. Most models focus on single field called the inflaton that drives the inflation. The inflaton is a lot like a cosmological constant in that it causes acceleration rather than deceleration, but it doesn't have a definite equation of state. The inflaton field is thought to arise from the symmetry breaking that occurs in the early universe (maybe 10^(-35) sec) when the strong force separates from the weak and electromagnetic forces.

Think of the inflaton as the order paramater for the grand unification phase transition. Like the magnetization of a ferromagnet, the order parameter is zero above a certain critical temperature and the system possesses lots of symmetry (full rotational symmetry for the magnet, symmetry between the strong, weak, and electromagnetic forces for the early universe), but as the temperature falls past the critical temperature, the order parameter becomes non-zero and the symmetry is broken (magnetization defines a preferred direction, strong force different from weak/emag force).

Rapid expansion ensues during a period called "slow rolling" while the scalar field looks for the minimum of its potential. During expansion, the energy density of all other kinds of matter/radiation becomes highly diluted. Once the slow rolling period ends the scalar field is near its minimum and begins to rapidly oscillate. This phase is called reheating becuase the oscillations of the scalar field heat the universe back up (it is very cold after inflation) and produce most of the matter/radiation observed today.

There is lots of room for further study in this picture. For example, how many inflaton fields are there and to what exactly do they correspond in particle physics (we have not yet observed any pure scalar fields, but most believe the Higgs will be found in the LHC experiment)? Also, the precise description of the reheating phase is still open for debate (since it depends on the nature of the inflaton field). The complete description of the initial symmetry breaking is also an open question.

Here is an online resource I found for further reading: http://arxiv.org/abs/astro-ph/9901124

Hmm, well, too bad it couldn't be as simple as imaginary mass spewing out at superluminal velocities.

-Dale

Going through space very, very fast will bring you face to face with a lot of very, very relatively high energy gamma photons
This got me thinking. The cosmic background radiation corresponds to black body radiation at 2.7 K. If you start traveling fast the CBR in front of you gets Doppler shifted to be black body radiation at a higher temperature. At .999998 c the CBR is the equivalent of a 3000 K plasma.

Basically, at that speed flying through empty space becomes the same as flying right into a star and the whole universe (or at least the half in front of you) becomes an opaque cosmic fireball. Bring some good sunscreen :cool:

-Dale

DaleSpam: you have asked what might be the explanation of the Guth Inflation. Once upon a time, I was thinking of this subject while not suffering from beer deprivation syndrome.

IF Lorentz contraction is a real physical effect,

IF there was a Big Bang,

IF there was a braking mechanism after the moment of the bang,

IF the first moment of banging saw bang stuff flying outward at c or even greater,

THEN, outward flying bang stuff, initially contracted to a mere wisp of its self would decontract ( I have invented a new word and I'm proud of it ) from a teensy itty bitty length to a relatively much longer length. Such decontraction ( please indulge me as I use my new word. I am easily amused. ) would be according to an enourmous numerical factor, having started at a virtually zero length. So we have enourmous expansion in a short time.

Since some small part of of my explanation might, in some faint way be slightly speculative, anyone can, if they dare, feel free to be a little skeptical, at least at first. :bugeye: