travelling faster than the speed of light

RolandIRL

hi all,
my physics lecturer was telling us that it is possible to go faster than the speed of light, just that information can't go faster. so what can go faster than light?

Podge_irl

A shadow. Nothing with mass (or indeed any encodable information).

del88

Podge_irl wrote: »

A shadow. Nothing with mass (or indeed any encodable information).

how can a shadow go faster?....it is light..

Podge_irl

No, it's the absence of light...

For that matter, if you shine a light onto the moon from Earth and move it quickly across the face of the moon, the "beam end" will be moving faster than light. No individual photons will be though, and no information can be transmitted faster thn light in this fashion.

del88

ye but it's not really moving as such...the beam end repesents a point in space time where one photon meets the surface of the moon ....what happens to another photon 2 seconds later or ten minutes later at a diffrent point in space time on the moon or anywhere else has nothing to do with speed....

Podge_irl

No, it's not moving as such. It's the only possible example of such a thing that I can think of and if the OP's lecturer wasn't referring to a similar scenario then I struggle to think what on earth he was talking about.

del88

If a had a light bulb and 2 photons left the light bulb from it's opposite sides ,then one photon would be traveling away from the other at twice the speed of light relative to each other but they could never exchange any information about each other because the information could never catch up.....i think

Podge_irl

del88 wrote: »

then one photon would be traveling away from the other at twice the speed of light relative to each other

Actually, no they wouldn't. They'd be travelling away from each other at the speed of light relative to each other. Although it's possible the language is just getting in the way here. As far as each photon is concerned, the other one is moving away at the speed of light. Form an observer's point of view the distance between them is indeed increasing at a rate of twice the speed of light. There is no way to exchange information between the two of them though.

Kevster

del88 wrote: »

If a had a light bulb and 2 photons left the light bulb from it's opposite sides ,then one photon would be traveling away from the other at twice the speed of light relative to each other but they could never exchange any information about each other because the information could never catch up.....i think

...loved that example dude. Very cool.

Iderown

Here you go - a limerick - how appropriate. It's not new, but I'm not sure who was the author, maybe Eddington.

There was a young fellow named Bright
Who travelled much faster than light.
He set off one day, in a relative way
And came back the previous night!

RolandIRL

i was watching this programme online last night. can't remember the name of it or the link, but i was thinking about could gravity act faster than light.
say hypothetically, that there was a sizeable distance between two stars, but the light from each of the stars had not reached the other yet. if there was a sizeable force of attraction between them, would the gravity from one of the stars influence the other even though their light isn't visible to each other yet?
could gravity act a distance away faster than the light could reach it?

Gurgle

whiteman19 wrote: »

say hypothetically, that there was a sizeable distance between two stars, but the light from each of the stars had not reached the other yet. if there was a sizeable force of attraction between them, would the gravity from one of the stars influence the other even though their light isn't visible to each other yet?
could gravity act a distance away faster than the light could reach it?

Yes and no - the mass which would become the stars was there before the stars started to emit light, so the gravity effect would 'reach' the other before the mass became a star.

RolandIRL

but say that the earth was moving at a velocity and the sun just appeared where it is now. would gravity act on the earth straight away or after 8 mins when the light had reached earth?
(i know this isn't possible but just for curiousity's sake, what if?)

Morbert

whiteman19 wrote: »

but say that the earth was moving at a velocity and the sun just appeared where it is now. would gravity act on the earth straight away or after 8 mins when the light had reached earth?
(i know this isn't possible but just for curiousity's sake, what if?)

It would take 8 minutes for the earth to be affected by anything the sun does. So if the sun suddenly disappeared, the earth would continue to orbit as if the sun was still there for 8 minutes.

robtri

it is possible for particles to travel at faster than light FTL speeds,
but:
nothing with mass can accelerate up to and faster than light as by the theroy of relativity that would requrie infinite energy....

but the theory does not rule out particles that have always been traveling FTL... i.e the hypotetical tachyon particle......

FISMA

Einstein did not say that there is nothing going faster than light. He in fact, held out that there might be a superluminal world, however, we would not be able to perceive it or understand it.

Einstein said that in our Universe, matter is bound by the speed of light. If you have mass you cannot go the speed of light. If you are going the speed of light, you cannot have mass.

A photon has no rest mass, obviously, photons do not rest, they go the speed of light.

E = mc^2 is just saying that mass and energy are equivalent. Hence the argument that to have mass is to have energy.

Imagine two space ships going 99%c towards each other. The gap is closing faster than the speed of light, however, no thing is actually going faster than c or at c.

As the speed of a particle, even an atom increases, so to does its mass. The universe does not have enough energy to accelerate even an atom of H to c.

That's also a problem for high speed space travel. Suppose we could get close to the speed of light. If I remember correctly the density of outer-space is about 1 atom/m^3. No big deal when you are going slow, pretty much a vacuum. However, when you are going fast, those atoms now look like bowling balls - :-(

However, if you could get to such a speed you would probably be clever enough to have a deflector shield or use them as energy for propulsion.

Killer Pigeon

Look into Heim theory.

http://en.wikipedia.org/wiki/Heim_theory

DublinWriter

A Tachyon maybe?

ApeXaviour

Kevster wrote: »

...loved that example dude. Very cool.

But it's wrong.

DublinWriter wrote: »

A Tachyon maybe?

Tachyons (hypothetical particle) can only travel faster than light as they have negative mass. If they existed they would violate causality in special relativity.

t4k30

I like, no love behaving myself.

Sheeps

Me too, that's why we are such good friends and continue to enjoy this fine bulletin board.