Does Light Have To Speed Off?

[Regulus (Trevor)]

Does a photon automatically travel at the speed of light?
If I created a photon in a vacuum would it automatically move off from it's point of creation at the speed of light?

[tilbrook@rbe.ne (Justin Tilbrook)]

Geez Trevor That's deep!

I think the answer is 42!


Cheers,

Justin.

[Varangian (John)]

I always understood that photons have no mass and they have infinite energy so always travels at the speed of light - potentially infinitely although this is debated.

[Regulus (Trevor)]

Thanks Justin
42 should be a theory since it seems to be the answer to so many questions :-)

[tilbrook@rbe.ne (Justin Tilbrook)]

Originally Posted by Regulus

Thanks Justin
42 should be a theory since it seems to be the answer to so many questions :-)

Agreed!

Certainly my standard answer when I don't know what the hell I'm talking about!

Cheers,

Justin.

[xelasnave]

Originally Posted by Varangian

I always understood that photons have no mass and they have infinite energy so always travels at the speed of light - potentially infinitely although this is debated.

I think you need infinite energy to propel matter to light speed however as a photon is with out mass a photon does not require infinite energy.

In respect to the original question I have no answer.
Alex

[mithrandir (Andrew)]

Originally Posted by Regulus

Does a photon automatically travel at the speed of light?
If I created a photon in a vacuum would it automatically move off from it's point of creation at the speed of light?

Yes and yes.
If they weren't traveling at c they would have no mass/energy and not even exist.

[Renato1 (Renato)]

It helps to remember the duality in the nature of light. Under some circumstances it acts as a wave, and under others it acts as particle.

So in your example, it has to travel at the speed of light. And the energy in a photon is very small.
Regards,
Renato

[FlashDrive (Poppy)]

If Trevor doesn't mind .. I have ... ' a sort of ' ... same question ..?

If ' you ' were travelling at the Speed of Light ... ' what would you " see " at all four points of the Compass. '

I myself have no idea .... maybe just a ' blur ' where ever you looked ... I dunno.

Col.....

[sheeny (Al)]

Originally Posted by mithrandir

Yes and yes.
If they weren't traveling at c they would have no mass/energy and not even exist.

Yes.

When a photon is created, it has finite energy (E = hv) and no mass, so the energy must move at c.

Think about it from the photon's POV: it does not experience time (because it moves at c in our reference frame) so only exists as a vector of energy from the start to where it is absorbed for an "instant". There is no option for it to exist at rest in our reference frame.

Al.

[sheeny (Al)]

Originally Posted by FlashDrive

If Trevor doesn't mind .. I have ... ' a sort of ' ... same question ..?

If ' you ' were travelling at the Speed of Light ... ' what would you " see " at all four points of the Compass. '

I myself have no idea .... maybe just a ' blur ' where ever you looked ... I dunno.

Col.....

Exactly as you have worded it, the answer is nonsense.

At the speed of light, time stops. Seeing, is an experience which requires time. So apart from the impossibility of reaching c, the experience of seeing at c is also quite impossible.

However, what I think you really meant is a thought experiment which has been around for as long as relativity. As you approach the speed of light, light approaching you from the front gets blue shifted further and further... ultimately you are speeding into a wall of gamma rays.

Likewise the light approaching from behind gets more and more redshifted, so behind you appears a very nearly dark void that appears to be very close to absolute zero in temperature.

To the sides, you would see the effects of length contraction as things would appear shortened in the direction you are travelling.

Extrapolating, you could reasonably argue that if you were able to travel at c and also able to experience time and perceive at c, you would see a hemisphere of gamma rays in front, a cold (absolute zero) hemisphere behind you and the entire visible universe compressed into the plane between the two.

Al.

[FlashDrive (Poppy)]

Originally Posted by sheeny

Exactly as you have worded it, the answer is nonsense.

At the speed of light, time stops. Seeing, is an experience which requires time. So apart from the impossibility of reaching c, the experience of seeing at c is also quite impossible.

However, what I think you really meant is a thought experiment which has been around for as long as relativity. As you approach the speed of light, light approaching you from the front gets blue shifted further and further... ultimately you are speeding into a wall of gamma rays.

Likewise the light approaching from behind gets more and more redshifted, so behind you appears a very nearly dark void that appears to be very close to absolute zero in temperature.

To the sides, you would see the effects of length contraction as things would appear shortened in the direction you are travelling.

Extrapolating, you could reasonably argue that if you were able to travel at c and also able to experience time and perceive at c, you would see a hemisphere of gamma rays in front, a cold (absolute zero) hemisphere behind you and the entire visible universe compressed into the plane between the two.

Al.

I understand and comprehend all that you have said here .... a ' plausible ' answer to the question..... but I don't see what is ' nonsense ' about it.
Maybe others have a different ' perspective ' on this and wish to contribute.

Col.....

[Regulus (Trevor)]

Thx Al, that seems like a good answer.

When a photon is created, it has finite energy (E = hv) and no mass, so the energy must move at c

Is that to say that to maintain it's existence as a discrete energy packet it needs to move (at speed relative to the our ref. frame), else the energy is...,what, re-absorbed into the quantum foam or is employed otherwise as part of another quantum construct, or some such???
(forgive the lack of conceptual terminology please, but perhaps u understand the gist of the question)
Trev

[sheeny (Al)]

Originally Posted by Regulus

Thx Al, that seems like a good answer.



Is that to say that to maintain it's existence as a discrete energy packet it needs to move (at speed relative to the our ref. frame), else the energy is...,what, re-absorbed into the quantum foam or is employed otherwise as part of another quantum construct, or some such???
(forgive the lack of conceptual terminology please, but perhaps u understand the gist of the question)
Trev

The photon doesn't maintain its existence. From its POV, it simply exists as a vector of energy from where it was emitted to where it is absorbed. Time has no meaning for the photon.

Quantum mechanics and the probability distribution affects when it is emitted in our reference frame, as well as other things. So once the photon is emitted, it simply exists. Where the photon is absorbed is determined by the energy vector of the photon - it has to be something able to absorb exactly that energy in the line of the vector. Deep in the core of a star that may be the atom next door, but it can't be the same atom it was emitted from.

Clear as mud?

Al.

[omegacrux (David)]

My head hurts

David

[Regulus (Trevor)]

Yes mate. now I got this mud on me I wont wash til some sinks in. Thx, it actually helped.

[Shiraz (Ray)]

I get a lot of pleasure from the thought that a few photons from the candles on my oldest grand-daughter's first birthday cake are now out the other side of Sirius. Which is kind of mind blowing in a way. persistent little beggars photons are and they don't just stop.