Speed of Light

[Matheous]

Currently- What is faster than light? (other than my wife finding a bargain)

[Trott]

nothing, light is faster than anything we know as it has no mass, therefore it does not increase its mass as it increases its speed which would slow it down.

[Matheous]

Čerenkov radiation :- " Some of these situations involve entities that actually travel faster than c in a particular reference frame but none involves either matter, energy, or information traveling faster than light."

http://en.wikipedia.org/wiki/Speed_of_light#.C 4.8Cerenkov_radiation

I found the above reference quite interesting although much of it above my limited comprehension.....
Thank you for your response.

[BigDave44]

When I did Relativity Theory at University (over 40 years ago) I seemed to be the only one that was unhappy with some of the nonsensical corollaries, like twin brothers going on separate space journeys and when they arrived back one was older than the other. At the time it was considered treasonable to query Einstein!!
Perhaps the answer lies in the recent work that suggests that the speed of light is not the constant that we once thought it to be:

http://www.sciencedaily.com/releases/1999/10/9 91005114024.htm

[fo3nix]

Accepted theory (that has been tested) suggests that the speed of light in vacuum, c, is a constant (except for perhaps the early universe).

But speed of light in some other material is a different kettle of fish. Then it's quite possibly to travel faster than this. If you do so, you can see effects like Cherenkov radiation. This is like a sonic boom (happening when you break the sound barrier), but for light. You get an eerie blue glow.

Some people do report breaking the speed barrier, but this is usually people getting confused between group velocity and phase velocity.

[Whickerman]

Trott - just because it's the fastest thing imaginable doesn't make it the fastest thing. Theoretically, if you could make a craft to travel at the speed of light, are you telling me that nothing could be expelled in front of that craft?

[BigDave44]

According to Relativity Theory, anything travelling at the speed of light has zero dimension in the direction of travel - so you'd be a bit squashed !!

[factor-fiction]

Whickerman wouldn't it be good if a craft could travel faster tha the speed of light.
It would allow us to see into the past.
Imagine- a craft flies off and travels at twice the speed of light. It then looks back and sees the earth as it was before it set off.

[CarlSagan]

That is only within our facility to observe, F30. It would not be looking back in time, merely looking at an earlier image. mirages in the desert are not there but are observable, rainbows only exist in your eye.

[Whickerman]

eeek... see, you'd catch up on light that's travelling in that direction, but the zero-dimension theory doesn't account for all the other directions that you can a) see, or b) be seen (it's relative), but either way the fact that you're travelling faster than you can be seen doesn't change the fact that you have a physical form and mass which I don't believe would change, and I'd love to argue the toss with einstein on that. I reckon between Einstein, Big Dave and myself it'd be an interesting night in the pub.

factor 30 - yes, it'd be interesting but you'd only need to travel at the speed of light plus a fraction!

[Symmetryigr8]

You couldn't make a craft that goes at or above the speed of light in a vacuum, as you get close to c and keep applying an accelerating force, the kinetic energy keeps increasing.
But there is an increase with mass instead of speed, it is very well observed with particles in accelerators that near c mass increases instead of speed. Any particle with no mass (neutrinos) in a given medium also travel at the speed of light in the same medium. But as soon as mass is added speed is limited.
Plus if you could reach it you would suffer from the zero dimension theory, time dilation reaching infinity, colliding with anything being fatal and length contraction reaching zero.

[Hymie]

Tachyons travel faster than light � check them out on Wikipedia for more info.

[Symmetryigr8]

If Tachyons exist. The effects I mentioned above have all been observed and measured. Also to make anything out of tachyons is useless. However check out the true idea behind star trek warp engines, instead of linearly traveling faster than light they 'fold' space time (allowable by current physics) to reduce the effective distance and s make the journey shorter, shorter than it would take light in a straight line.

[jake-the-peg]

I wonder if I can clarify a few things.

Firstly we know of nothing within the Universe that can exceed c - the speed of light in a vacuum

Cherenkov radiation occurs when the speed of light in a material is exceeded. That is not the same as exceeding the speed of light in a vacuum

Special relativity does not say that nothing can exceed c.

It takes the fact that the speed of light in a vaccum is fixed as an experimental starting point and works from there.

Yes Wickerman that is *exactly* what is meant - check out the Michaelson-morley experiment for the proof.

Tachyons - Nothing with any mass can travel at the speed of light - the equations however do not stop anything from travelling faster ( we get a complex number as a result ). It was for a while thought that some particles might have been able to "tunnel" the speed barrier and exceed the speed of light but nobody's ever seen the slightest bit of evidence for this so it's one of those great ideas that just turned out not tobe the case!

Finally It is believed that in the very early part of the Universe's existance it expanded in size many times faster than the speed of light ( Check out the inflationary period and Alan Guth). The relativity laws only apply within the Universe, they don't apply to the Universe itself.

Big Dave -if you're not happy with paradoxes in relativity - stay well clear of Quantum mechanics! :c)

Beware of trying to force the physics of extreme bodies into the common sense developed from your life experience in a narrow range of physical conditions

[Matheous]

http://web.archive.org/web/20001121064300/www. public.iastate.edu/~physics/sci.physics/faq/FT L.html

Some interesting FTL stuff above.
I thank all who have offered theories and arguments for & against FTL -but I can't help thinking at some time in the past it must have been thought 'impossible' to travel faster than sound ! -I do appreciate that is a bad comparison but I always keep an open mind when the word 'impossible' is used....

[Mortartube]

I've invented a car that travels at the speed of light, but I can't seem to get the headlamps to work.

[Rev. Green]

The phenomenon known as Collapse of the Wave Function occurs faster than light, but it cannot be used to transmit information faster than c.

[Ridcully]

I believe information is allowed to travel faster than light - by quantum entanglement it can depart from A and arrive at B simultaneously. However, given that the concept of simultaneity isn't valid in a relativistic framework, I don't quite understand...

[Rev. Green]

Quantum Entanglement is what happens before Collapse of the Wave Function.

If two related particles travel apart (at a speed not exceeding the speed of light) then when something happens to one of them this can cause something to happen to the other instantly.

For example, the particles might have their spins in opposite directions. So if you found the spin of the first to be upwards then the second would have its spin downwards.

Here is a way to make money by apparently sending information faster than light:-
Sit in a spaceship about as far away as the Sun and say that you can tell whether your partner on Earth is holding the Ace of Spades or the King of Diamonds within a minute of him choosing.
People will take your bet because it would take 8 minutes for your partner to tell you.
However, your partner sends you one of a pair of entangled particles. He waits 8 minutes for you to receive it, then he measures the direction of spin of the other particle of the pair. If it is up he chooses the Ace of Spades. If it is down he chooses the King of Diamonds. You measure the direction of spin of your particle and can instantly tell the spin of your partner's particle and consequently you know which card he has picked. You win the bet.

Of course you could just arrange for your partner always to pick the King, perhaps he should "go short" on bank shares instead, then let you amaze your friends in the spaceship by predicting whether the shares would rise or fall.