Can we travel faster than the speed of light?

[Luke*]

Im only 14 and I am having a argument with a friend and teacher, and I need to know is is possible in theory to go faster than the speed of light and what is it? Time travel whatever, they don't believe me that you can and I remember reading it somewhere but the fact is no one knows how to do it yet. Please help would be greatly appreciated, sorry if this is quite a stupid q.

 

[ranger]

These types of questions have been asked many times. Refine the search if you like.
http://www.google.com/search?hl=en&...+light+site:www.physicsforums.com&btnG=Search

 

[Schrodinger's Dog]

Assuming special relativity is correct no, we can't. We generally assume relativity is correct at the moment, so you would be wrong. The speed of light is the speed limit for the Universe, as far as we know and as yet no one has disproven this fundamental law.This thread might help:-

https://www.physicsforums.com/showthread.php?t=166095&highlight=Faster+than+light

The Universe has a fundamental symmetry, called Lorentz symmetry, which causes to exist an asymptotic^* upper limit on all relative speeds. Objects with mass can never reach that upper limit. Massless objects (such as photons) must travel at that limiting speed, and no other. These are consequences of the mathematics of Lorentz symmetry.

This obviously begs the question, "why does the universe have Lorentz symmetry?" Nobody knows. (Or at least there is no generally accepted answer, as far as I know.) This is the ultimate answer to all "why?" questions in physics, by the way. The answer to any "why?" question leads to another "why?" question, and ultimately we always come to one that we cannot answer in the context of physics, at least not yet.

^* An asymptote is a value that can be approached but never reached. Except in the case given here.

 

[Luke*]

Thanks, appreciated, but I am sure there was something that said there is a way to travel faster than light in a sense ie travel between solar systems ie through time or something. I don't know if they were right but that's what they said. Any ideas? One of them was bending the universe if i remember.

 

[ranger]

Thanks, appreciated, but I am sure there was something that said there is a way to travel faster than light in a sense ie travel between solar systems ie through time or something. I don't know if they were right but that's what they said. Any ideas? One of them was bending the universe if i remember.

You may be interested in reading this article:
http://en.wikipedia.org/w/index.php?title=Faster-than-light&oldid=143154648

 

[cristo]

No, one cannot travel faster than the speed of light. It sounds like you have read something highly speculative, which may or may not have any sensible background. There have been reasonable suggestions for faster than light travel, such as wormhole theory proposed by Kip Thorne, but these are still entirely theoretical.

I suggest that, if interested, you learn special relativity instead of attempting to have arguments with your teacher. SR is easily accessible to anyone with knowledge of high school algebra.

 

[cristo]

You may be interested in reading this article:
http://en.wikipedia.org/w/index.php?title=Faster-than-light&oldid=143154648

I would strongly advise against recommending a wikipedia article that says this site requires verification by an expert to a layperson attempting to learn the basics. Instead, this page may be of interest.

 

[Schrodinger's Dog]

There are cheats that enable you to seem to travel faster than light, but you never actually do, for example in the highly speculative idea of bending space using high gravity,so you could shorten the distance between two points. However at no point did you actually travel faster than light, you just got there much faster than you could if traveling in normal space at the speed of light. I so wish that made as much sense on paper as it did in my head

Hyperspace another sci fi concept involves the bending of space so far it breaks an you end up in some sort of area outside of space. Hyper space is pseudo scientific though like sub space in Star Trek.

 

[Winzer]

While I know that matter cannot exceed the speed of light due to GR, I have heard somwhere that there have been quasars moving 2C.
Is this true or hogwash?- probably hogwash.

 

[cristo]

While I know that matter cannot exceed the speed of light due to GR,

It's actually SR that asserts this.

I have heard somwhere that there have been quasars moving 2C.
Is this true or hogwash?- probably hogwash.

Obviously I don't know exactly what you've read, but I would conjecture that it has to do with the speed of recession of distant galaxies (or in this case quasars). It does appear that distant galaxies are traveling away from us at speeds greater than the speed of light; however the actual motion of the galaxies is less than the speed of light, with the other apparent speed generated by the fact that the universe is expanding.

 

[CraigD]

While I know that matter cannot exceed the speed of light due to GR, I have heard somwhere that there have been quasars moving 2C.
Is this true or hogwash?- probably hogwash.

Not hogwash, just mis-stated. You can observe quasars moving away from us at 2c. The problem here is that they are not actually moving through space at 2c, but the space between us and it is expanding at a rate equal to 2c. Because space has no mass, it can expand at any rate; i.e. 2c.

To the original question, the true statement would be that nothing with mass can move through a vacuum greater than c.

CraigD, AMInstP
www.cymek.com

 

[Winzer]

Not hogwash, just mis-stated. You can observe quasars moving away from us at 2c. The problem here is that they are not actually moving through space at 2c, but the space between us and it is expanding at a rate equal to 2c. Because space has no mass, it can expand at any rate; i.e. 2c.

To the original question, the true statement would be that nothing with mass can move through a vacuum greater than c.

CraigD, AMInstP
www.cymek.com

Thanks for the clarification Craig D.

 

[Luke*]

Thanks Cristo, just read all of it, really got me into things a bit more and a lot more insight into FTL travel etc. Thanks again.

 

[Robert100]

Wait a tick, space doesn't actually expand.

Not hogwash, just mis-stated. You can observe quasars moving away from us at 2c. The problem here is that they are not actually moving through space at 2c, but the space between us and it is expanding at a rate equal to 2c. Because space has no mass, it can expand at any rate; i.e. 2c. To the original question, the true statement would be that nothing with mass can move through a vacuum greater than c.

CraigD, AMInstP

Wait a minute, this can't be right. I know that it is common to say that "space expands", but that really isn't so. Physical objects move through space, the metric used to describe these objects expands along with them. But it is the physical objects that control the metric. There is no mysterious creation of new space in-between already existing objects. See this recent paper, which clarifies confusion on the phrase "expanding space".

http://www.arxiv.org/abs/0707.0380

"Expanding Space: the Root of all Evil?"
Authors: Matthew J. Francis, Luke A. Barnes, J. Berian James, Geraint F. Lewis
(Submitted on 3 Jul 2007)

Abstract: While it remains the staple of virtually all cosmological teaching, the concept of expanding space in explaining the increasing separation of galaxies has recently come under fire as a dangerous idea whose application leads to the development of confusion and the establishment of misconceptions.

In this paper, we develop a notion of expanding space that is completely valid as a framework for the description of the evolution of the universe and whose application allows an intuitive understanding of the influence of universal expansion. We also demonstrate how arguments against the concept in general have failed thus far, as they imbue expanding space with physical properties not consistent with the expectations of general relativity.

This is discussed in the new thread on this forum:
https://www.physicsforums.com/showthread.php?t=176380

Robert

 

[Robert100]

Can we travel faster than the speed of light? See these 2 websites

Im only 14 and I am having a argument with a friend and teacher, and I need to know is is possible in theory to go faster than the speed of light and what is it? Time travel whatever, they don't believe me that you can and I remember reading it somewhere but the fact is no one knows how to do it yet. Please help would be greatly appreciated, sorry if this is quite a stupid q.

This is not a stupid question. It is a fascinating and important question, which touches on the principles of both special and general relativity. The short answer is this:

* Most ideas about traveling faster-than-light (FTL) are based on a total misunderstanding of Einstein's theory of special relativity. FTL, in any simple way, is impossible.

* Some ideas about FTL are based on a misunderstanding of quantum mechanics. As we understand QM, there is no way that any information (let alone objects!) can be transmitted FTL. There may be a tiny amount of wiggle room left to find some loophole in this, and research is ongoing, but don't let your hopes be lifted. It is almost certainly forbidden in any way.

* Einstein's theory of general relativity does seem to allow for traveling faster than light, under very special and nearly impossible circumstances. No one has ever tested these specific predictions, and no one knows for certain if such FTL, or time travel, is actually possible.

I won't get into it here, but I believe that FTL travel (via wormholes, which is a sort of cheat) may be possible, but time travel is impossible. That's my opinion, and nothing more.


See these websites for details:

http://en.wikipedia.org/wiki/Faster-than-light

http://www.math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html


Robert

 

[olgranpappy]

p.s. The link to baez's page is pretty cool. Luke, if you have not yet found it there is an explanation of how one can travel to the center of the galaxy (which we measure to be 30000ly away) in a relativistic rocket in what feels like only about 20 years to the astronauts in the rocket (of course much longer than 30000 years pass on Earth so it's not really FLT travel, but it could be what you are looking for).

here's a link:

http://www.math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

 

[country boy]

I’m surprised that no one has mentioned tachyons in this thread.

 

[olgranpappy]

I’m surprised that no one has mentioned tachyons in this thread.

it was mentioned implicitly in this link:

http://www.math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

see #19.

 

[Schrodinger's Dog]

I’m surprised that no one has mentioned tachyons in this thread.

I think the reason they're not explicitly mentioned is they are hypothetical, thus the sentence "the speed of light is the speed limit for the Universe, as far as we know", is still is perfectly consistent, that and such hypothetical ideas merely confuse the issue and may well be wrong anyway.

 

[cristo]

I think the reason they're not explicitly mentioned is they are hypothetical, thus the sentence "the speed of light is the speed limit for the Universe, as far as we know", is still is perfectly consistent, that and such hypothetical ideas merely confuse the issue, without breaking any fundamental rules or creating any unresolvable issues.

Even if tachyons weren't hypothetical, there would be no problem with the speed of light being a local limit. Just like massive particles must travel at speeds less than c, and particles with zero mass must move at the speed of light tachyons would always have to travel at speeds greater than the speed of light. So, the speed of light really is a limit that any particle cannot pass through.

 

[Schrodinger's Dog]

Even if tachyons weren't hypothetical, there would be no problem with the speed of light being a local limit. Just like massive particles must travel at speeds less than c, and particles with zero mass must move at the speed of light tachyons would always have to travel at speeds greater than the speed of light. So, the speed of light really is a limit that any particle cannot pass through.

I know but imaginary mass? Do we really need to go into the properties of hypothetical particles

for all values v>c\rightarrow

E = \frac{mc^2}{\sqrt{1 - \frac{v^2}{c^2}}}\rightarrow E = \frac{mc^2}{i}\rightarrow m=\frac{E.i}{c^2}

I am well aware they would change nothing, but they are hardly well accepted hypothetical particles. Most people think they belong only in Star Trek anyway, is what I meant by confusing the issue.

I originally wrote out some stuff detailing what they were etc, but I deleted it all so as not to confuse the issue.

To clarify what I mean by confusing the issue

 

[ObsessiveMathsFreak]

I understand how special relativity shows show objects cannot travel faster than the speed of light, in any inertial frame. The part I didn't understand is how this means that "action at a distance" type phenomena are also prohibited. For example, why it is that gravity or quantum entanglement are prohibited in the SR framework. It didn't seem to extend itself to these effects from what I saw.

 

[Luke*]

Some other interesting points, I would love to argue or debate these points, but the fact that I don't understand some the stuff posted, I will have to learn over the next few days if possible, which is the only obstacle. If that makes any sense. ;]

 

[meopemuk]

I understand how special relativity shows show objects cannot travel faster than the speed of light, in any inertial frame. The part I didn't understand is how this means that "action at a distance" type phenomena are also prohibited. For example, why it is that gravity or quantum entanglement are prohibited in the SR framework. It didn't seem to extend itself to these effects from what I saw.

You are absolutely right. Superluminal propagation of classical particles is inconsistent with the principle of causality. However, "action at a distance" is not forbidden by this principle. The key is in the less-known fact that in any quantum relativistic interacting theory (where the Hamiltonian H = H_0 + V has interaction term V) the boost operator \mathbf{K} = \mathbf{K}_0 + \mathbf{W} must be interaction-dependent too (see S. Weinberg "The quantum theory of fields" vol. 1, eq. (3.3.20)). You can find more discussion in

E. V. Stefanovich, "Is Minkowski space-time compatible with quantum mechanics?", Found. Phys., 32 (2002) 673; http://www.geocities.com/meopemuk/FOPpaper.html

and section 11.1 in

E. V. Stefanovich "Relativistic quantum dynamics" http://www.arxiv.org/physics/0504062

 

[Demystifier]

Meopemuk, are you Stefanovich?

 

[Voltage]

Look at his profile.

 

[Feldoh]

You can cheat to go faster than light, I think it's been done with water, since it's more dense then air the speed of light slows down doesn't it?

 

[dkgolfer16]

Feldoh...the speed of light is constant through any medium...water does not slow it down...and no you cannot cheat and go faster then it!

 

[Feldoh]

Feldoh...the speed of light is constant through any medium...water does not slow it down...and no you cannot cheat and go faster then it!

Well c doesn't but, that's only in a vacuum. In water you'd need to take refraction into consideration. The velocity of light in water slows down enough that electrons can actually move faster than light. Think it's called cherenkov radiation. Or at lesat I thought that's how it worked XD

 

[Cusp]

no - you can't travel (locally) fast than light (in a vacuum)

 

[Holocene]

Why is the speed of light the speed that it is?

What laws of physics govern its speed?

 

[rbj]

Why is the speed of light the speed that it is?

What laws of physics govern its speed?

i am presuming that you mean the speed of light in vacuo, not the ostensible speed of light in some transparent material, no? we've been to this question before ("why is c?") and the best answer i can give you is that it is not the salient meaningful question. similar questions can be asked about other dimensionful physical contants and those question are likewise not the salient meaningful questions.

the gravitational constant, G; the speed of propagation (EM, gravitation, information, whatever is your "instantaneous" action), c; Planck's constant, \hbar; permittivity of free space, \epsilon_0; these are all numbers that are purely human constructs resulting on how humans chose to define units of time, length, mass, and charge. note the 4 constraints and the 4 unknowns (that are eventually measured in terms of these anthropometric units). i know that the meter is now defined to be the distance traversed by light in 1/299792458 second, but that wasn't the original definition, for the sake of illustration, let's revert the definition of the meter back before 1960.

now, if instead, you measure everything in terms of Planck units, the values for all these constants become 1, 1, 1, and 1/(4 \pi). the only numbers given to us by Nature are dimensionless numbers. so, to ask "why is the speed of light equal to 299792458 meters per second?" causes us to ask the more basic questions that are "why are there about 6.1821 x 10³⁴ Planck lengths in a meter?" and "why are there about 1.8549 x 10⁴³ Planck times in a second?" those are the meaningful questions.

you see, if we measure and describe everything in Planck units, there simply is no c, or G, or \hbar, or 4 \pi \epsilon_0. those numbers just go away from all of our algebraic equations of physical law.

we know that the meter and second are determined to be related to our experience of reality. a meter is approximately how big we are. and a second is, well, not the absolute shortest period of time in our bioological perception, but close to it. somewhere i read that, at our prime, we can do about 20 basic logical operations or computations (crude compare operations) per second in our conscious mind, don't know if that is true or not. when we get older, our CPU slows down but we got a better database.

so then we might start asking, why are there about 10²⁵ Planck lengths in the Bohr radius (about the size of atoms)? and why are there about 10⁵ atoms in the length of a biological cell? and why are there about the same number of cells in the length of a sentient organism like us?

you could construct similar questions about physiological processes regarding why it takes about 10⁴⁰ Planck times for us to do anything with our bodies (without tools). there is a relationship of the speed of our consciousness and the time around a second. if we were tiny insects, a second might seem like a long period of time. but then we wouldn't be thinking about why the speed of light is what it is. suppose we lived for 1000 years and it took us what we now consider a minute to think every new thought. we wouldn't be manuvering cars at 100 km/hr and i don't think a second would be our unit time and the speed of light would seem even faster to us.

you answer those questions, then you'll get close to why the meter and the second are as big as they are (relative to some Natural units), and, from that, you'll have an idea why the speed of light (which as far as Planck units are concerned is just 1, not some dumb and arbitrary number like 299793458) is what it is, from our perspective.

the speed of light (and of all things instantaneous) is just the natural speed of things in the universe of which to reference all other speeds against.

now the Elementary Charge, that's something else, since the natural unit of charge is already defined. it's interesting (to me at least) that the electron charge, relative to the Planck charge, is just \sqrt{\alpha}. one can say that e is what it is because of the value of the fine-structure constant (this important dimensionless number that the universe does give us), or (what i prefer) the fine-structure constant is what it is because of the amount of charge that Nature has bestowed upon electrons and other charged particles. because i think that they should have normalized \epsilon_0 and 4 \pi G instead of 4 \pi \epsilon_0 and G, i think the most natural units would come out slightly different than the Planck units (but be the same order of magnitude) and then, measured in these natural units, the electron charge would be \sqrt{4 \pi \alpha} which is about 0.30282212 . VERY close (as far as orders of magnitude go) to unity. i think 0.30282212 is the number theoretical physicists should put on their walls instead of 137.035999679 . i think the latter flows from the former.

those are the sort of numerical "why?" questions i might be wondering about.

 

[Krelian]

Well there is a theorem that was proofed somehow, but not generally accepted. Bell's theorem, where it implies that any entangled particle can transfer information instantly. Well the idea is that this is a "non local" effect, while general relativity is "local".

The problem here is that you can verify the Bell's inequity experimentally, but the interpretation it was given, to think that the reality is non-local, and everything is entangled, could give you into some problems and ideas that will tell you that you could travel faster than light, or quantum transportation (you could "think" you are instantly transporting information).

The actual idea came from Einstein, Polanski, and Rosenberg, 1934 paper, the possible ways to solve this paradox included "hidden variables", "many worlds", "non locality" and others.

The "non local" idea came also from the regularization in quantum field theory to deal with infinite would eventually give you a "non local" action.