Ok – so this goes to the very core of physics as we know them so before you read on – I ask you to open your mind just a tad here.

Not so long ago we thought that just below the speed of sound was the fastest a human can travel without something ‘star-treckish’ happening to him (or her).

I would like to question the speed of light.
We know that light can be bent around large objects by gravity, so in my mind it would seem pretty safe to say that some of the light which directly hits the large object creating that gravity must have been sped up as it neared it, by been pulled towards it just like the light ‘bending’ around the outside.

In my mind – if something can be bent by a pull off to the side then surly it can be sped up by a pull in front or slowed down by a pull from behind (i.e. Black Holes, the gravitational pull is so strong that the light cant escape – been pulled back). And if the light of speed is a variable depending on the environment in which you observe it – then how can it stand that our current measure of the speed of light is the fastest any thing as we know it can travel?

Isn’t light just waves?
Just like sound?

We can and do manipulate the speed of sound waves and many others – why can’t we do the same to light? (asides from the energy required) Or can we?

I have heard a whole lot of people saying this just isn’t possible, but I’m yet to be told just ‘why’ this isn’t possible. It seems to be more of a belief than a fact.

Can anyone shed any light on this?
Cheers!
Darren

Well, part of the answer is that sound and light are different. Sound needs a medium (air, water, solid) through which it can travel, where as light travels quite well and quickly through a vacuum.

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Insanity: doing the same thing over and over again and expecting different results.
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Mmmm... we call it a 'vacuum' - yet we agree that our "vacuum" is actually made up of something which we dont understand yet - Dark Matter. Our vacuum we call space isn't emtpy - just as the space between you and the clouds isn't emtpy.

I agree with the sound comment (of course) - maybe lights medium is something other? Maybe everything has and needs a medium, only some of the medium's we dont understand yet. And maybe that medium is the one which will give us the same control over light as we have over sound.

Ta for reply!!
It's all food for the brain.

Smiles!
Darren

According to my understanding of history, we used to think we couldn't go faster than sound because there was some "barrier" that we didn't understand. Every time we tried to fly an aircraft to break the sound barrier, the aircraft began to shake and shimmy and generally become uncontrollably unstable as it approached mach 1 (speed of sound). But finally we figured out how to control the stability of aircraft better and proceeded to break the sound barrier.

You can manipulate the speed of sound only by changing the medium through which is travels. You can't artificially make a sound wave go faster in any given substance than it normally does, except perhaps by fiddling with the temperature of medium its travelling through. Light speed is a totally different matter. There appears to be a definite principle in effect that governs its speed,... or rather our own relative measurement of its speed. According to relativity, we can never measure light going faster or slower than c in any given medium. Light breaks all the common sense rules and it's behavior often seems counter-intuitive. For example, it appears to need no physical medium in which to travel even though it can be detected travelling through space as discrete quantums as photons or as waves.

Finally, I know I have shed very little light on the original subject/question, but I should mention that light does not speed up when it approaches an object like a star. It's wavelength or frequency is changed, but the photon or wavefront of the light still travels at c regardless.

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h34r: i have read the posted issues on light, and i would like to add the following, if you gaze up to the night sky , and look at the dots of light , and wonder , what am i seeing now, well what you are seeing in front of you is a picture of the universe as it was possible millions of light years ago.''''''''', you are only seeing a light image of it, yes , nothing you see is real in the current time scale, its only an image , did you realise that, there is no substance to what you are seeing,only an image, therefore to travel faster than light, yes faster than light, you need to transfer mass, and not the light image of it, maybe if you could re-organise the molecules of mass and charge them to re-assemble in another place then you would have instantanious trasnfer of matter over infinite distance.

:blink: if god (in the catholic sense), created the earth in 7days, then how long did it take him to create the iniverse.!!!!!!!!!

No light's velocity is not altered by the presence of massive objects like black holes, white dwarfs, etc. in it's vicinity. Light is not waves like sound waves. Light is made up of individual massless particles called photons that _always_ travel at velocity c (approx 300,000 km/s) in a vacuum (in other mediums like air, glass, water and odd things like Bose-Einstein condensates it's more complicated and light can sometimes travel faster or slower than c). Due to the quantum principle of wave-particle duality light can sometimes appear to be made of of waves and other times it behaves like particles, so it's very different from sound which is always waves and requires a medium like air or water to travel through (sound waves are really only changing pressure regions moving through a medium like air--no medium no pressure differences and so no sound).

This velocity, c, of light in a vacuum is completely independent of the velocity of the observer or other influences like gravity, magnetism, etc. It is constant and unvarying and is therefore called the "universal constant". Under the influence of gravity light does not slow down or speed up like non-zero rest mass particles (protons, neutrons, electrons, etc.) that make up normal matter do, it changes it's frequency and so either gains or loses energy that way instead. E.g. a light beam directed away from a neutron star, a black hole or any body with gravitational mass loses energy and so is red-shifted (it's frequency drops) as it climbs out of the body's gravity well, if emitted towards the massive object from some distance away in space the light will be blue-shifted (its frequency increases) and so gain energy from the increasing gravity as it approaches the object, but in both cases its velocity does not change, it will still be c. Now it's path will also be bent or curved according to the General Theory of Relativity due to the warping of spacetime around the massive body, but its velocity does not change.

Only particles like photons that have "zero rest-mass" can travel at c, anthing with a non-zero rest-mass like normal matter can only travel slower than c no matter how much energy is applied to it. As a body made up of non-zero rest-mass particles approaches c it's mass increases and it's length decreases--all according to the equations of Special Relativity. At velocity c the body would have infinite mass (and would require infinite energy to give it this velocity) and zero length; which is obviously impossible. Thus normal non-zero rest-mass bodies can only ever travel slower than c, never at c or faster than c. With sufficient energy being applied they can however approach arbitarily close to c, e.g. 99.9999978% of c like they do in particle accelerators and so forth.

How come light photons can travel at c then? Because their "rest-mass" is zero and so the infinite mass and zero length issues do not apply. A body with a rest-mass of zero will still have a mass of zero when it's travelling a velocity c, unlike a body with non-zero rest-mass (no matter how tiny) which would have infinite mass at velocity c (and zero length) and so can never reach this velocity. Photons in fact can only travel at c, they cannot travel slower than c in a vacuum, which is why they don't respond to gravity the way non-zero rest-mass particles do.

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David S.

"Why are the pretty ones always insane?"
-- Chief Clancy Wiggum, The Simpsons.

After reading all of the above, I have three observations/questions:

1- How can frequency of light change without changing its speed?

2- Photons are bosons - in other words, light has its own carrier particle (photons); sound doesn't have its own carrier particle. That is one of the main distinctions between light and sound.

3- When a beam of light encounters a gravitational field, the gravity changes the photon's direction - not its speed (this does not hold true for theoretical black holes - of course, as we all know, light gets sucked in). Photons (ligh) bend AROUND the sun - not into it.