Light speed

[markystars]

One of my interests in space is lightspeed. I find it fascinating and always try to watch any programs that are connected to it.

One thing that no program answers though is where light gets its energy from to travel at that speed in the first place. I understand how it has no mass and therefore CAN travel at that speed without needing infinate power but i dont get what actually propells it at that speed.

Would be interested if anyone has any answers

Thanks

Mark.

[wulfrunian]

This isn't really a complete answer, but I think at least part of the answer is that not only can light travel at that speed, but it has to. Nothing "propels" it or accelerates it to that speed, it's unable to ever travel any slower.

Maybe another part of the answer is to take an example of the creation of light... in the centre of the sun, a reaction takes place which fuses hydrogen atoms and produces helium. A by-product of this reaction is gamma radiation, which has an amount of energy determined by the fusion reaction. By the time this radiation's made it from the core of the sun to the outside world, some of it has lost enough energy to become visible light.

[Doc]

Light is massless it requires no force whatsoever for light to travel at lightspeed. Also remember that space is a vacuum, I agree not a perfect vacuum but still pretty good so there will be little friction to count for, and also space itself is expanding at the speed of light.

[brianb]

Light is a particular piece of the electromagnetic spectrum, it moves at the speed of light because that's the solution from Maxwell's field equations with the specific physical constants of this particular universe.

As to where the energy comes from - if the light is coming from a bulb, the energy comes from the electrical power used to heat the filament up to high temperature. The filament gets hotter until the energy radiated away in light (and infra red, and ultra violet - actually for an ordinary incandescent light most of the energy radiated is in the infra red) balances the power consumed. In a fluorescent lamp, the electrical energy is converted into ultra violet light by discharge through a metallic vapour, the UV is then absorbed by the tube lining which fluoresces, re-radiating the energy as visible light. Much more of the energy is in the visible spectrum which is why fluorescent lights are brighter for the same power input. Light can also be generated by bombarding phosphorescent compounds directly with an electron beam, as is done in old fashioned cathode ray tubes, and by a number of other physical processes.

[markystars]

Thanks for the replies,

So when everything in the universe had died out i.e stars has all burned out and galaxy's eventually dissapear leaving nothing (the big freeze theory, if that's what happens), will the light that those stars etc gave off still be travelling around the universe?

[brianb]

will the light that those stars etc gave off still be travelling around the universe?

Yes, except that most of it will have hit something (dust), been absorbed & re-radiated at longer wavelengths quite a few times ... eventually everything will be in equilibrium with the remnant radiation from the Big Bang .... if the dark energy hasn't asserted itself in the Big Rip by then, in which case there'll be nothing at all left in the universe, or rather every subatomic particle will be isolated in its own universe so that there's no longer anything for any interactions to take place with, and therefore the concept of "travelling round the universe" ceases to have a meaning.

[markystars]

great answer, thanks.

i am even more impressed by lightspeed now

[Sunwind]

it's a lot easier to understand when you realise that "light" is just radiation, it's not really a special thing, just the way we look at it

[markystars]

Good point, didnt really imagine it like that before, but now it makes more sense when i think of it like that rather than a beam of objects

[Aldebaran5]

If there wasn't any dark energy then would light travel faster!!

Keith.

[Kit-Fox]

Meta-Light is almost an idea rather than a phenomenon. It is the light by which darkness can be seen, and therfore is always available, everywhere. If it didnt exist, darkness could not be visible. It is widely used in the film industry for shots in caves & mines.

A cookie goes to anyone who calls me on that explanation

[Highflight]

So, how fast exactly, is the speed of light?

[brianb]

So, how fast exactly, is the speed of light?

No-one knows, not being able to measure exactly ....

... The best estimate for the speed of light, in a vacuum, is 299,792.458 km/sec with an uncertainty of one or two in the last digit.

[Steve922]

The big question is :-

Why is the speed of light constant at that velocity irrespective of the observer?

Answer THAT and I suspect that you will know at once what Mass, Space and Time actually are (and probably everything else about the universe(s) .) Before that, we can only try to find a set of rules or 'laws' which try to explain what we observe happening and specualte as to why.

Steve

[brianb]

Why is the speed of light constant at that velocity irrespective of the observer?

Go read Einstein's seminal 1905 paper on Special Relativity. It's not especially hard going, and answers all the questions. In fact Einstein started making his theory based on the assumption that the speed of light would always measure the same irrespective of the motion of the observer.

[dark knight]

If the Universe is expanding at the speed of light, does this mean we will never see beyond our own local system, since the expansion and speed at which light travels would cancel each other out? would that explain blackholes?

I've probably not posed that correctly and hope it makes some sense...

[Steve922]

Go read Einstein's seminal 1905 paper on Special Relativity. It's not especially hard going, and answers all the questions. In fact Einstein started making his theory based on the assumption that the speed of light would always measure the same irrespective of the motion of the observer.

Talk about missing the point! :-) After the observational evidence in the late 19th century that the speed of light appears to be constant for all observers irrespective of their frame of reference, Einstein (and others) attempted a mathematical explanation as to how this calculates out and how it affects mass, space and time.

Einstein made no attempt to explain WHY this is so. Let alone to answer ALL questions.

Steve

[PeterMammoth]

Actually, everything in the universe, including us, are traveling through spacetime at the speed of light. We tend to neglect the time element of spacetime when we think about movement. Light itself does not perceive the passage of time, so all it's speed goes into the three space dimensions. For us, we are traveling through time as well. Basically, if you take into account four dimensional spacetime, everything is moving at the speed of light.

[markystars]

so if we are all travelling at the speed of light, then when i start running, am i going faster?

Also, i wonder what the view of lets say beetleguise would be if you started off on earth looking at it and the travelled at the speed of light towards it, assuming that in reality it has exploded by now but we dont know cuz the light hasnt reached us, it would be like travelling through time as you would see perhaps the explosion and the aftermath in a shorter amount of time than it actually took so you would be in effect travelling into the future, correct me if im wrong on that though (ignoring the fact that it would still take more than our short lifespans to get there)

[Stryda]

it would only appear to be in the future...from earth...as its actually still the same time, just different light that we see. Technically time is not measured by light so by simply travelling faster than light we arent travelling forwards in time, but rather just seeing the photons earlier than we normally would (in regards to long distances (ly)) ....or am i talking rubbish?

[markystars]

i see what your saying, but events would surely happen at a faster rate giving the illusion of traveling into the future? or is it ME that is talking rubbish lol

[Stryda]

i see what your saying, but events would surely happen at a faster rate giving the illusion of traveling into the future? or is it ME that is talking rubbish lol

I also see what your saying hmm i guess if u continued to travel faster u would see things happen at a quicker rate, or maybe, if u travel faster than the speed of light, u cant even see light? :hello2:my theory ...are we both talking rubbish now? lol

[markystars]

I think so LOL

[markystars]

I should stick to Doctor Who i think lol

[themos]

Travelling into the future is trivial, you just have to keep running (like The Doctor does). it's going back that seems impossible.

By the way, going to Betelgeuse should not take that long. From the point of view of a speeding rocket, distances appear contracted by the Gamma factor making for a shorter journey. Assuming constant acceleration of one-g for half the journey, followed by constant deceleration of one-g for the rest, we can get to Vega in less than 7 years, the centre of the galaxy in about 20 and the Andromeda galaxy in about 28.

The Relativistic Rocket