Why is the Speed of Light the Limit?

[DeletedUser21]

Why is the Speed of Light the Limit?

Is it because our universe is being created on planck length at a time at the speed of light?

Corresponding blogarticle from Youtube: .

Discuss!

[orudge]

(can't embed Youtube movies inline)

Yes you can, with the [youtube] tag. Just do [youtube]http://normal-youtube-url-goes-here[/youtube]

[petert]

(Corresponding blogarticle from Youtube (can't embed Youtube movies inline)).

Hijacking your post a bit, but it works for me:

[Brianetta]

Didn't hear any new ideas in that video at all. Every idea and "way of visualising" mentioned therein is something of which I've known for at least a decade.

[Nextra]

The speed of light (I don't think) is so much of a limit as more of a barrier much like the speed of sound. If your wondering why I would say this, look up the Alcubierre drive. It is theorized that it would be possible to go faster than the speed of light and this has been shown on an atomic scale (the cooling ponds at a nuclear reactor glow blue because the electrons are being emitted at speeds exceeding c) and its more now, just finding a pratical large scale model on which to do so.

[Voyager One]

OK, you'll probably call me a crazy Trekkie but...
I agree with Nextra - it's a technological barrier. Folding space and time continuum might do the trick for speeds faster than light but all this is still just an SF topic since the technology is far far away from this. Who knows, maybe some day... I live in hope of that.

[Nextra]

Well if you jump back even 100 years, it was thought that it would be impossible to go faster than the speed of sound as they thought the pressure that builds up in front of the vehicle would be that great at the sound barrier that it would certainly cause structural failure of the vehicle.

My own personal beliefs on this is that the speed of light is a constant on all frames of reference to act as a standard to measure everything against. Why that standard is the speed of light I do not know, but it is an effective point to work from.

[planetmaker]

Why that standard is the speed of light I do not know, but it is an effective point to work from.

The speed of light (in vacuum!) is universally the same, irrespective of the inertial reference frame an observer is placed in, i.e. independently whereever in the universe you are. What better reference could there be?

[michael blunck]

[...] (the cooling ponds at a nuclear reactor glow blue because the electrons are being emitted at speeds exceeding c)

No, they´re not. You´re mixing up "phase velocity" http://en.wikipedia.org/wiki/Phase_velocity of light with the "vacuum speed" of light http://en.wikipedia.org/wiki/Speed_of_light

HTH
regards
Michael

[Brianetta]

The speed of light (I don't think) is so much of a limit as more of a barrier much like the speed of sound. If your wondering why I would say this, look up the Alcubierre drive. It is theorized that it would be possible to go faster than the speed of light and this has been shown on an atomic scale (the cooling ponds at a nuclear reactor glow blue because the electrons are being emitted at speeds exceeding c) and its more now, just finding a pratical large scale model on which to do so.

The speed of light in a vacuum is the fastest speed there is. It's neither a limit (in the everyday sense) nor a barrier. You cannot punch through it. It's a limit in the pure maths, calculus sense. No matter how fast you're going, it'll require infinitely more energy to accelerate you to the speed of light. Time dilates and mass increases as you accelerate, and all the maths add up.

An interesting extra here is that particles that are going faster than light already (such as tachyons) can be sped up as much as you like, but slowing them down to the speed of light would require infinite energy.

Cerenkov radiation is analogous to the sonic boom, in terms of light rather than sound, but the important fact here is that the speed of light in a transparent material is slower than the speed of light in a vacuum. The photons aren't going any slower, but they aren't taking a perfectly straight path, and it's possible for energetic particles to overtake them by taking the direct route. That's an over-simplification, but the key point here is that even if you go faster than light does in that material, it's not because you found a way to go any faster.

That warp bubble idea has one fundamental flaw. Assuming you work out how to make such a bubble (at least these are theoretically known). You stretch spacetime behind you, and compress it ahead, and you're nearer your destination without travelling faster than light. Congratulations; now you have one problem remaining. How do you cross all that compressed space-time quickly, to actually reach your destination? It's the same amount of spacetime that you were going to have to cross anyway. There's no current mathematical evidence to say that it'd be quicker (or possible), placing that propulsion method firmly in the "speculative fiction" category.

Personally, I think we (as a species) will just learn to adapt to sub-FTL travel. The subjective journey can be relatively short (just decades to the local stars) and we'll learn to deal with the practical problems of time dilation, which means that every traveller effectively travels forward in time a few centuries, depending on the velocity. It becomes a society problem then, and other minds can solve that.

[CommanderZ]

The speed of light (I don't think) is so much of a limit as more of a barrier much like the speed of sound. If your wondering why I would say this, look up the Alcubierre drive. It is theorized that it would be possible to go faster than the speed of light and this has been shown on an atomic scale (the cooling ponds at a nuclear reactor glow blue because the electrons are being emitted at speeds exceeding c) and its more now, just finding a pratical large scale model on which to do so.

The speed of light in a vacuum is the fastest speed there is. It's neither a limit (in the everyday sense) nor a barrier. You cannot punch through it. It's a limit in the pure maths, calculus sense. No matter how fast you're going, it'll require infinitely more energy to accelerate you to the speed of light. Time dilates and mass increases as you accelerate, and all the maths add up.

An interesting extra here is that particles that are going faster than light already (such as tachyons) can be sped up as much as you like, but slowing them down to the speed of light would require infinite energy.

Cerenkov radiation is analogous to the sonic boom, in terms of light rather than sound, but the important fact here is that the speed of light in a transparent material is slower than the speed of light in a vacuum. The photons aren't going any slower, but they aren't taking a perfectly straight path, and it's possible for energetic particles to overtake them by taking the direct route. That's an over-simplification, but the key point here is that even if you go faster than light does in that material, it's not because you found a way to go any faster.

That warp bubble idea has one fundamental flaw. Assuming you work out how to make such a bubble (at least these are theoretically known). You stretch spacetime behind you, and compress it ahead, and you're nearer your destination without travelling faster than light. Congratulations; now you have one problem remaining. How do you cross all that compressed space-time quickly, to actually reach your destination? It's the same amount of spacetime that you were going to have to cross anyway. There's no current mathematical evidence to say that it'd be quicker (or possible), placing that propulsion method firmly in the "speculative fiction" category.

Personally, I think we (as a species) will just learn to adapt to sub-FTL travel. The subjective journey can be relatively short (just decades to the local stars) and we'll learn to deal with the practical problems of time dilation, which means that every traveller effectively travels forward in time a few centuries, depending on the velocity. It becomes a society problem then, and other minds can solve that.

I still hope there is some solution to the FTL travel problem. If there is not, we will be confined to Earth for thousands of years at least. And I don't want to see social consequences of this, I just don't believe we can sustain Earth and our society for another thousand of years.

[michael blunck]

The speed of light in a vacuum is the fastest speed there is. [...]

There may be many vacua with different values for c [1]. Special relativity doesn´t forbid FTL, but existence of "tachyons" is purely hypothetical. Even if they´d exist, that would not help in FTL communications [2]. With regards to Alcubierre, this is only an idea. Problems range from mathematical sound formulation to the unability to engineer something like (non-existing) negative energy densities. However, the general idea of manipulating space time has already been verified in cosmological inflation theory, but again, in fact that´s not FTL travel [3]. With regards to FTL communications, even modern experiments on nonlocal correlations (EPR) have been shown not to be useful in transmitting (classical) information FTL, but preserving relativistic causality.

[1] http://arxiv.org/abs/gr-qc/0107091
[2] http://prola.aps.org/abstract/PR/v159/i5/p1089_1
[3] http://en.wikipedia.org/wiki/Comoving_distance

I still hope there is some solution to the FTL travel problem. If there is not, we will be confined to Earth for thousands of years at least.

Even with space travel STL the whole galaxy could be populated in a relatively short time.

regards
Michael

[Voyager One]

Whatever scientific answer you post here, I still hope there WILL be a USS Enterprise...

[CommanderZ]

Even with space travel STL the whole galaxy could be populated in a relatively short time.

Unless "relatively short time" are millions of years for you, I doubt so.

Let's say we have a stardrive able to reach 90% c (for simplification let's make it accelerate from 0 to its max. speed instanteously).

Milky Way has cca 100000 light years in diameter. Solar system is cca 15000 light years from the outer rim, which gives us travel distance to the furthest star of approximately 85000 light years (note I am ignoring relative star movement and the fact the starship probably wouldn't be able to travel through the galactic core). The result is...95000 years.

Code: Select all

In[1]:= Convert[Convert[85000LightYear,Meter]/(0.9SpeedOfLight),Year]
Out[1]= 94509.1 Year

Now, we wouldn't send a huge colony ship(s) supposedly carrying at least millions of people (otherwise the colonization would be irrelevant to total earth population) to an unknown star. So we would send a scout ship in first, which gives us 300 000 years for a colony ship to reach the star.

Yeah, relatively short time.

[planetmaker]

Whatever scientific answer you post here, I still hope there WILL be a USS Enterprise...

There is already: http://en.wikipedia.org/wiki/USS_Enterprise_(CVN-65)

[michael blunck]

Well, time to answer the OP´s question:

Why is the Speed of Light the Limit?

Because of Einsteins´s general relativity theory which is generally accepted to be valid in its realm. It links the vacuum speed of light c to the space-time continuum. Speed is a local value and thus limited by special relativity theories as well. In fact, there exists no Lorentz transformation transforming time-dependant vectors into space-dependant vectors. In addition, as pointed out from other people here, accelerating matter towards c needs increasingly more energy, and to reach c would need both unlimited energy and unlimited time. Only massless particles are able to travel with speed equal c. In addition, information may not be transmitted faster than light because this would destroy the fabric of causality.

Remains the question why c is equal to 299.792.458 m/s? This seems to be depending on the way our universe had come into existence, in the same way like other universal constants (fine structure constant, proton-to-electron mass ratio, coupling constants for strong and gravitational forces, ..) got their exact numerical values. There is no reason why these values should be the same in other universes, though.

HTH
regards
Michael

[Voyager One]

There is already: http://en.wikipedia.org/wiki/USS_Enterprise_(CVN-65)

I meant the other one... Actually I prefer the Voyager.

[Brianetta]

Yeah, relatively short time.

You don't know how close to the truth you came. Your subjective journey time could be arbitrarily short, for arbitrarily huge amounts of available energy. We could all go and colonise Barnard's Star, and make the journey in a subjective two week trip. Aside from the odd colour and position of other nearby stars, it'd seem perfectly normal. One week accelerating, one week decelerating. Do the same on the way back... that's when you experience the social effects of fast interstellar travel. At least thirteen years went by on Earth, assuming we just dropped of colonists and came back for supplies. Let's hope we left them with enough, because we left them there something like seven years ago, not a fortnight.

Social problems, is all. If we can get some real oomph into our propulsion, we can go anywhere, quickly; as long as we bear in mind that the rest of the universe will race ahead to preserve causality.