How Does Light Move and What Propels Photons?

[Naty1]

I agree with you jnorman and I love the summary that I once read (can't remember where !) Light takes no time to get from one point to the next and for light there is no distance between one point and the next.
Wish I understood it !

I believe you are saying that light does not experience time, as it travels at c and according to the math time should stop at that velocity. I'd say that the math simply doesn't work when you input a velocity of c into the equations, so you cannot depend on it.

Such stuff, which is ok intuitively to some extent, leads to comments like this, which I like:

Eternity is no time at all for a photon.

Richard Feynman may have been the wise guy [genius] who coined that, I'm not sure. But it sounds like something he would have said!

I think the math does 'work' but just for light;it's not a realistic result. The issue is that 'nothing' [no mass, no test instrument] can ever reach the speed of light so nothing can be in the frame of light. One way to understand this is that no matter how fast you think you are going, locally light will always pass you at 'c'...so 'nothing' can attain such speed 'c'. The math tells you that IF you are moving at speed c ,as a photon does, time appears to stop and [Lorentz-Fitzgerald] length is zero. [You can't use photons to measure any time delay because they don't age!]

Hence the other common adage:

Photons don't age.

 

[truesearch]

It was a mistake to state that 'typical' light came from electrons in a nucleus.
This mistaken statement appears to have been backed up in post *10 my a 'science advisor' no less.
I hope that we would all agree that mistakes of this sort must be corrected.

 

[truesearch]

'We all know there are no electrons in the nucleus' yet we all know (!) that beta radiation (electrons) come from the nucleus.
Physics is fascinating.

 

[Bobbywhy]

'We all know there are no electrons in the nucleus' yet we all know (!) that beta radiation (electrons) come from the nucleus.
Physics is fascinating.

“An unstable atomic nucleus with an excess of neutrons may undergo β− decay, where a neutron is converted into a proton, an electron and an electron-type antineutrino.”
http://en.wikipedia.org/wiki/Beta_particle

 

[Leland]

Photon has kinetic energy, and therefore it moves.

 

[sophiecentaur]

Momentum, yes. But KE? How would you detect it?

 

[Subductionzon]

Is there a way to measure the kinetic energy of a photon using relativity? I know you could try to measure it with Newtonian mechanics but I am pretty sure that the answer would be wrong.

 

[Drakkith]

Is there a way to measure the kinetic energy of a photon using relativity? I know you could try to measure it with Newtonian mechanics but I am pretty sure that the answer would be wrong.

Not really. Per the definition from wiki:

The kinetic energy of an object is the energy which it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest.

A photon requires no energy to accelerate up to c, it simply moves at c always. Furthermore, a photon could never be decelerated either. In addition to that, a photon always moves at c regardless of who is observing it, which means that it's kinetic energy could not be based upon it's motion, as it moves at the same velocity in all frames yet it's energy differs.

 

[truesearch]

I have received an 'infraction' as a result of my posts following post *10.
Therefore, as much as I would like to contribute to this discussion I fel that I must keep quiet.

 

[Drakkith]

I have received an 'infraction' as a result of my posts following post *10.
Therefore, as much as I would like to contribute to this discussion I fel that I must keep quiet.

Well, as long as you don't do whatever the infraction was telling you not to do you should be fine!
And don't worry too much. An infraction is like a "notification" that just tells you that you've done something you maybe shouldn't have. It's not a warning and it doesn't count against your points on the forum. It's just there to let people know they've strayed a little too far from the main road before they get too far off and start to get warnings and such.

 

[truesearch]

what I did was to repeat what a 'science advisor' did... I quoted his/her quote.
I am interested in physics not other peoples quotes.
Say no more about it... let's concentrate on physics

 

[sophiecentaur]

Is there a way to measure the kinetic energy of a photon using relativity? I know you could try to measure it with Newtonian mechanics but I am pretty sure that the answer would be wrong.

You could 'infer' a value for KE, perhaps, but not measure it. In any case, the energy of a photon is just its energy and of an type that is specific to photons. Why should it be related to half m vsquared? (If it doesn't have a mass) People make the same mistake about the momentum of a photon and try to relate it to an mv definition.

 

[Leland]

My bad, momentum is a much better word.