photon acceleration?

[YT2095]

as with all things, speed starts from Zero and then reaches whatever speed the energy supplied to it will allow.

 

does the same apply to Photons? you have a torch switched off (there`s no photons being emited) then you power up and there`s light, do these photons go from Zero kms/sec to 300,000 kms/sec instantly or does it take a little time?

 

and how do we know?

[blike]

When photons are created they are travelling at 300,000km/sec already.

 

How do we know?

 

Set yourself back a known distance. Measure the time between when the flashlight is switched on and you see the photon. You can then extrapolate whether or not the photon has always been travelling at c (or at a known speed in a given medium).

[blike]

Also, I believe some of einstein's theories dictate that nothing can ever accelerate to the speed of light. I don't know whether this applies to photons though, someone else will have to answer that.

[YT2095]

Set yourself back a known distance. Measure the time between when the flashlight is switched on and you see the photon. You can then extrapolate whether or not the photon has always been travelling at c (or at a known speed in a given medium).

but doesn`t "time" not really apply at those speeds, over a long distance I can see how the effect would be negligable and be 300k kms/sec, but over a short distance maybe a meter would give a clearer result as to any acceleration as it doesn`t have the distance to even out to an average, but to measure over 1 meter would be nearly impossible

[Radical Edward]

no, the same does not apply to photons. They have zero rest mass and hence always travel at c.

[YT2095]

so from Zero to C in no time?

[Aeschylus]

so from Zero to C in no time?

 

No, because the photon is never at rest in any inertial frame, when your a photon your born at c and you die at c.

[YT2095]

Hmmm... so it would seem that the rate of acceleration only applies to things with Mass then?

and as a photon has no mass, it can effectively "get away with " instant velocity?

[Aeschylus]

Hmmm... so it would seem that the rate of acceleration only applies to things with Mass then?

and as a photon has no mass' date=' it can effectively "get away with " instant velocity?[/quote']

 

It's important to relaize that the phton never accelartes or deccelrate sit always has a velcoity of c.

 

Instant velcoity is not peculair to the photon, imagine an electron-posiron annihilation in some refernce frame which produces lets say produces two pions. These two pions will in most refence frames have some velocity when emitted without having to accelerate t reach this velcoty(of course unlike the photon they will have a rest frame), indeed if this was not the case 4-momentum could not be conserved.

[alt_f13]

Could someone explain to me how a photon will always move at 300 grand regardless of the velocity of the reference frame it is observed from? I forgot what my hs physics teacher told me.

[Aeschylus]

Could someone explain to me how a photon will always move at 300 grand regardless of the velocity of the reference frame it is observed from? I forgot what my hs physics teacher told me.

 

It's a postulate of special relatvity that comes from experimental evidence.

 

If you want to no how mathematically objects always appear to travel at c then imagine that that your intertial refernce frame and you observe a space ship travelling with velocity u and another object travelling in the same direction with a velocity v. Someone aboard the spaceship will see the object travel at velocity v' given by the formula

 

 

 

[math]v' = \frac{v - u}{1-\frac{vu}{c^2}}[/math]

 

When v = c

 

[math]v' = \frac{c-u}{1-\frac{u}{c}} = \frac{c(c-u)}{c-u} = c[/math]

[alt_f13]

Awesome, thanks. But I still have no idea how that is possible in practice.

 

Clues?

[Dave]

I suppose my answer would be "it just is"; a postulate can't really be proved, just like the axioms of mathematics are assumed to be true.

[swansont]

I suppose my answer would be "it just is"; a postulate can't really be proved, just like the axioms of mathematics are assumed to be true.

 

It's also shown in Maxwell's equations - the EM speed of propagation is invariant under coordinate transforms,which was a big clue for Einstein with relativity in trying to make the transformations work properly for other aspects of physics. That light was an EM wave was a fairly recent discovery at that time, and I think a lot of kinks were in the process of being worked out.

 

Physics doesn't answer the fundamental question of "why" in the attempts to explain the behavior of nature - just the "how."

[TheProphet]

Awesome' date=' thanks. But I still have no idea how that is possible in practice.

 

Clues?[/quote']

 

I'd like too say that light keeps itself at C at all times! Due to the fact that at C, T = 0. So in order for light to keep being the splendid bearer of energy it is! it keeps time at Zero, therfore it always travels at C in all reference frames. That way u never loose energy wherever u are or how u are measuered! Photons can only be absorbed and ejected att C. Altough photons can deviate C (both +/-) but on large scales it remaines a Constant C. I might have done this a tad more unclear too =) but aiänt that just fun !

[YT2095]

ok, I`ll accept your answers, I find it hard to "picture" with any frames of reference I`m familiar with, But I accept it

 

nothingness to C in an instant, where do they come from then? what part of an atom do they reside in, I`m guessing the electron? and since a photon has no mass, an emitter of photons should be able to do this forever without reduction in mass?

[TheProphet]

ok, I`ll accept your answers, I find it hard to "picture" with any frames of reference I`m familiar with, But I accept it

 

Thing is.. Light need no frame of refenrece as we do... very hard too picture.. trust me.. i had a headake for a couples of days figuring it out *lol*

 

nothingness to C in an instant' date=' where do they come from then? what part of an atom do they reside in, I`m guessing the electron? and since a photon has no mass, an emitter of photons should be able to do this forever without reduction in mass?[/quote']

 

Photons (acording to me) should be rather freely disturbtions on global strings! they start instantainously! but they have no mass right.. byt energy they do posses! So an atom emitting photons will att first hand lose energy.. not mass.. but if no energy were able to be taken, and still a photon sprung to life. Mass must be affected! and probaly some other particle would have been created out of that emitting electron! Since if the mass of an electron should be altered the electron should aslo be destroyd!

[swansont]

what part of an atom do they reside in, I`m guessing the electron? and since a photon has no mass, an emitter of photons should be able to do this forever without reduction in mass?

 

No, photons are created and annihilated, they aren't "stored" in other particles. And since they possess energy whatever emitted them will see a mass change. Also you can create mass from the photons under the appropriate conditions.

[YT2095]

that`s the E=MC2 bit right?, has that ever occured where it`s worked in the other than obvious Atomic weapon type direction, where Photons have done the reverse and made Mass?

[swansont]

that`s the E=MC2 bit right?, has that ever occured where it`s worked in the other than obvious Atomic weapon type direction, where Photons have done the reverse and made Mass?

 

Yes. Photons of sufficient energy make particle/antiparticle pairs. electron/positron pairs take minimum 1.02 MeV (the rest mass energy), and the process can be seen in bubble chambers and similar detectors.

[Guest bellebeam]

Can someone explain what antimater is (besides what the name implies)? Thanks

[swansont]

Antimatter

[Severian]

There are plans to build a photon collider as an offshoot of a electron-positron linear collider. The important thing is not how fast they can go, but how much energy they have, so their mass (and the fact that they travel at c) doesn't come into it - after all, on the scale of a TeV, electrons are effectively massless too.