Light Speed

[confuddled]

Sorry if this is really simple - please forgive me :)

I seem to remember from a physics class (many, many years ago) that it is impossible in theory for an object to travel at the speed of light

a) is this true? but more importantly :

b) if a large craft was designed that COULD travel for example 1mph under the speed of light, if someone was walking on the craft in the same direction that it was travelling, would they therefore be moving faster than light?

Many thanks in advance and sorry for being a bit of a dunce when it comes to this sort of thing

[Loosehead]

c = speed of light below....

a) Yes, so the current theories say

b) The current theory also states that c is constant regardless of the speed of the observer so if you where travelling a 1 mph slower than c then then light would still be at it's usual speed and time would have almost stopped.

The time/c relationship has been well tested using atomic clocks.

[mibn2cweus]

If you were moving one mile per hour slower than the speed of light (c-1mph) relative to another person observing you than time for you would be such that two miles per hour in any direction would only be about a one/three billionths of a mile per hour different as seen by the person observing you; in other words time for you would be dilated accordingly and you would only be moving at two mph relative to the speed of light from you own perspective.

The speed of light is constant for all observers, (even you), only the time continuum (the apparent speed at which events take place) changes relative to whose observing whom. When you returned from your journey your clock (the one you took with you) would show this discrepency in time when compared to a clock that stayed at home.

I hope this make some sense, it takes a little getting used to.

[fo3nix]

a)

no, the above answers are wrong.

it is quite possible for objects to travel at the speed of light, and in fact many are doing so right now: photons of light!!

however, only things with no mass can travel at the speed of light. for those that have mass (even very small mass) it is impossible (if you believe the theories of relativity) for it to travel at the speed of light.

b) the above answer this part sufficiently so I shall not repeat. it's all relative!

[Loosehead]

"the above are wrong" "It's quite poissible..... photons of light" But not a "Large craft" as mentioned in the original question. Thanks so much for confirming we are correct with B.

Strangled by your own pedantry fo3nix, what a plonker.

[fo3nix]

hehe sorry, but it _is_ true for an object to travel at the speed of light (as the original question phrases it). but yes, granted, not the sort of objects the questioner may have been thinking of.

[Mr Slappy]

But surely light has mass? How can an object not have mass and still exist? If the theory is correct then light should be infinitely heavy.