Light speed travel.

[styley]

Say I was to get on a space ship capable of travelling twice the speed of light. I head off into space at the speed of light for two years. Then I turn and head back to earth at twice the speed of light. Would I pass myself on the way back and would only the three years have elapsed on earth when I got home?

[andrea81]

I would say so yes! But if I were you, before you do make sure you dont go into warp speed, you may get back before you left!

[fo3nix]

The question has no answer, because it makes no sense.

Light speed is a hard limit. You can't break it. Massive objects can't even travel at it, only close to it.

Any answers are thus in the realm of science fiction, where anything at all is possible!

[jno]

in theory the speed of light is the ultimate speed possible. However, in news this month...

http://www.news.com.au/heraldsun/story/0,21985 ,22255966-663,00.html

not being a scientist, I can't even begin to explain this.

[styley]

Who says you can't break light speed fo3nix. Is it the same guy who wrote the bible?

[jake-the-peg]

I don't think Einstein wrote the bible Styley

Firstly special relativity doesn't say that massive bodies cannot travel faster than light.

It says that they cannot travel at the speed of light - there is an implication that you need to travel at the speed of light to get faster than this but there are quantum reasons for thinking that this just might not be the case.

It was suggested many years ago that particles called tachyons might exist formed in the big bang that travel faster than light - however nobody has ever found any evidence of them so it's pretty much a dead end.

With regard to the quoted story here's an explanation:

http://arstechnica.com/news.ars/post/20070816- faster-than-the-speed-of-light-no-i-dont-think -so.html

[fo3nix]

jno: I am a researcher, and can tell you that that story isn't worth much.

jake: I agree.

styley: The speed of light being the max. speed limit of the universe can be derived fairly easily from the mathematics of relativity. Quite a bit different to the Bible.

However, as jake says, the speed of limit is like a brick wall on the speed of things. While anything on our side of the wall (less than speed of light) can't go past it, it doesn't exclude the possibility of there being other things on the other side of the wall that can't come into our side. These are the Tachyons that jake talks about.

Still, even with these particles that have only been theoretically predicted, it won't allow for you to travel at twice the speed of light.

[jno]

thanks for the enlightenment, jake and fo3nix; just more bad science then.

[styley]

Well, say for example, one is travelling on a craft which is travelling at exactly the speed of light. If you were to run along the craft in the same direction as it is travelling, would you not then be travelling faster than the speed of light?

[fo3nix]

No, because nothing that has mass can actually travel at the speed of light. Only light itself. Perhaps the odd other thing (neutrinos, for one), but I don't think they do. A hot topic though.

[jake-the-peg]

Actually it's not so much that relativity shows that hte speed of light is fixed but that this was discovered and Einstein took this and the principle that things are the same for a moving observre and built special relativity from that.

Now you may ask how it was discovered that the speed of light was fixed - it was a brilliant experiment by two Scientists called Michelson and Moreley.

They were looking for something else at the time and is probably the world's greatest failed experiment

http://simple.wikipedia.org/wiki/Michelson-Mor ley_experiment

Their experiment is like shining a torch from a moving train - the light still moves at c not c+speed of the train - only they used the Earth not a train

[styley]

Ok then. You are in a craft travelling at 1kph slower than the speed of light. On the outside of said craft is a large arm connected onto it parallel. This arm swings around at 50kph. Surely this must be travelling faster than speed of light when it's in motion as its external to the craft and is part of the "interference".

[mibn2cweus]

Velocity is relative to the reference frame of the observer.
As an object accelerates and approaches the speed of light relative to the point it started its acceleration from, it does not take that starting reference frame with it but acquires a reference frame of its own where it is as rest relative to itself no matter what velocity it acquired in between. An object in uniform motion is at rest in its own reference frame and in spite of any velocity it has gained relative to its starting point the velocity of light remains the same. It is the passage of time that adjusts to accommodate the constant velocity of light in two separate reference frames, not the velocity of light.

Look at the following scenario and see if it helps you to grasp the difference between what is observed in two separate reference frames.

A space ship resting on a launch pad takes off and accelerates to 90% of the speed of light relative to its starting point and shuts off its propulsion system temporarily. It is now coasting along at 0.9c and the occupants no longer feel any acceleration or that they are in motion at all. The only clue that they are moving is that when the pilot looks back towards the launch pad it appears to be receding steadily at about 0.9c.

Now the pilot releases the first stage that has spent its fuel and it appears to be floating nearby nearly motionless (accept for the bit of motion it acquired in the process of separating from the rest of the space ship). They are both moving in uniform motion relative to each other while continuing to coast away from the launch pad at the amazing velocity of 90% of the speed of light!

So what will happen now when the pilot again blasts off from this point and again accelerates to 90% of c relative to the first stage of the spaceship that he left behind? Will he then be going (.9 + .9) 1.8 times the speed of light?

cont. . .

[mibn2cweus]

No! The sum of both accelerations work out to be closer to 98% of the velocity of light relative to his original starting point (the launch pad). How is this possible? How did he manage to defy the laws of arithmetic? The answer to this riddle lies in the dilation of time that takes place as one approaches the velocity of light. Although he undertook an identical acceleration using the same amount of energy and his clock appears to be ticking at the same rate it always did, his time is passing at a reduced rate relative to the passage of time as measured in the reference frame he departed from.

No matter how many times he repeats the same acceleration he will never reach the velocity of light because time will just keep stretching out to accommodate the constant velocity of light.

Hope that helps you with understanding the implications of your questions.

[andrea81]

What if he put 'go-faster' stripes on?

[jackthehat]

Yes!
As Einstein hadn't predicted the existence of 'Go-Faster' stripes, should that have any impact on his 'Special Theory of Relativity' ?

[styley]

By jove I think he's got it. Still think it's possible to break light speed but. Possible. I'd say it will be done, not through propulsion, but through, em, what word am I looking for? (I think it will be done by pulling ourselves towards an object rather than propelling towards it). Is there a term for that?

[juliacornwal]

Lawks, I've just read all this lot and it reminded me of watching an episode of the documentary series Horizon. I didn't understand a word - but I loved it!!

[wildwood]

It is possible to exceed the speed of light, if you're a galaxy.

The universe is expanding at 1.8 times the speed of light (or so they say).

[styley]

Tell that to most of the above wildwood.

[fo3nix]

wildwood: that's not true.

The spacetime itself is expanding faster than the speed of light, perhaps... cosmology isn't the most concrete thing just yet.

What's crucial is that spacetime can do things that matter cannot; matter cannot exceed the speed of light, unless it is light itself (or some other massless particle).

So no, galaxies are not travelling at more than the speed of light.