Speed of light

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Let me preface this question by saying that it might be silly because I might have the facts wrong, but I'll ask anyway.
If a photon is a "little packet/bundle of energy", the photon (energy) should contain some mass, even if it is tiny, since Einstein stated mass and energy are interchangeable. Now when this mass is accelerated toward the speed of light it needs energy to "push" it to a higher speed. When the photon starts getting closer to the speed of light, the energy that it takes to get it there starts to cause the particle to gain mass until it reaches a point where the energy it takes to overcome light speed would be infinite.
My question is that if the photon has so much energy how come when a photon hits a human it doesn't "knock him/her out cold"?

Like I said this may be a stupid question. I think I am just missing something really easy that I should know, so feel free to rip my statement apart and add any new info I am missing.
 

mathman

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Photons have zero rest mass. Photons travel at the speed of light from the time they are born. They do not speed up from a slower speed. You cannot think of them as small masses being speeded up. They do not have "infinite" energy, or anything close to it.
 
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What causes them to travel at the speed of light. Are you saying that they go from zero to 180,000 miles per second in an instant?

P.S. Im not questioning you to be stubborn, I'm just trying to get the answer :approve:
 
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pervect

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CBR600RR said:
What causes them to travel at the speed of light. Are you saying that they go from zero to 180,000 miles per second in an instant?

P.S. Im not questioning you to be stubborn, I'm just trying to get the answer :approve:
Photons never speed up, or slow down. They travel at 'c' from the instant they are created.

The situation in a physical media gets a bit tricky. One of the best ways of thinking about it is that the photon travels at 'c', always, even in a media, but occasionally gets absorbed and re-emitted.

Note that the speed of energy transmission through a media thus can be slower than 'c', due to the photons being absorbed, held for a very short while, then re-emitted.
 
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CbR

Depending on the frequency and interaction with different electromagnetic waves, photons "can knock you out cold "
 
who said that photons dont hit the humans?!!

photons have momentum, since they have mass.

but the problem is in the misunderstanding of the nature of the photons mass.Photons have relativestic mass, but not a rest mass.

even though, it still has momentum, and that was proven..
 

Chronos

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Photons do not have mass. They do have momentum. Only massless particles are permitted to travel at c, in fact, they are forbidden to travel at any other speed.
 
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I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?
 
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Since a photon is generated by an electron, they're both right.
 

Chronos

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CBR600RR said:
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?
Gravity bends space. Photons always travel the shortest distance between two points [a straight line]. In curved space, the shortest distance between two points is a geodesic [a curved line].
 
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CBR

All in all your question is actually a brilliant question. Physicists argue if photons are EM or just a wave duality of a particle without mass.
There is no consclusive answer as of today.
 

selfAdjoint

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CBR600RR said:
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?
The general relativity gravity couples to energy density, not just mass. Light does not have mass, but it does have energy, and thus it gravitates.
 
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Would the rest mass of photons actually be non zero, then the theory of quantum electro-dynamics would have to be re-written :confused:
 
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chroot

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Virtually all of existing physics would have to be rewritten for the photon to have mass. Simply put, every experiment ever done to date would not have have worked if the photon actually had mass.

- Warren
 
One of my friends told me that photons would have to have mass or they couldn't exist. I told him that if they did have mass a photon would knock you on your arse and turning on a light would cost you a fortune when your power bill arrived.
 
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UNLESS, the entire light theory as we know it is reversed.
What IF photons are constantly in the air, but connect to an electron the moment it is energized - it connects to it at the speed of light ...........when it becomes visible, or not, depending on frequency.
 

pervect

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CBR600RR said:
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?
Photons are affected by a gravitational field. But in GR, energy generates the gravitational field, not mass. To be more precise, it's the stress-energy-tensor that generates the gravitatioanl field - under most circumstances, however, only the component T_00 of this tensor, which represents energy density, is important.
 

Chronos

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whydoyouwanttoknow said:
One of my friends told me that photons would have to have mass or they couldn't exist. I told him that if they did have mass a photon would knock you on your arse and turning on a light would cost you a fortune when your power bill arrived.
Your friend is incorrect. A photon has no mass, merely momentum. He is, however, right about the power bill.
 
Chronos said:
Your friend is incorrect. A photon has no mass, merely momentum. He is, however, right about the power bill.
I said the power bill would cost you a fortune. That'd be correct right propelling a particle with mass to the speed of light.
 

Chronos

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Oops said:
CBR

All in all your question is actually a brilliant question. Physicists argue if photons are EM or just a wave duality of a particle without mass.
There is no consclusive answer as of today.
That question has already been answered. As far as I can see. The fact you have a computer that works is pretty compelling evidence.
 

Nereid

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whydoyouwanttoknow said:
I said the power bill would cost you a fortune. That'd be correct right propelling a particle with mass to the speed of light.
If the particle had mass, it could never be propelled to the speed of light, even if the power company had access to all the energy in the universe ... of course, if the particle were an electron, and the power company allowed you to have as much power as a small city (and you could covert the energy to making the electron go faster efficiently), your electron would be moving very close to the speed of light :wink:

Do you know how to calculate how close to the speed of light it would go?
 

Chronos

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Nereid said:
If the particle had mass, it could never be propelled to the speed of light, even if the power company had access to all the energy in the universe ... of course, if the particle were an electron, and the power company allowed you to have as much power as a small city (and you could covert the energy to making the electron go faster efficiently), your electron would be moving very close to the speed of light :wink:

Do you know how to calculate how close to the speed of light it would go?
My guess would be very close to c. I am curious, nereid, why you waited so long to jump in?
 

Nereid

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'long'? The thread only began after 22:00 on the 17th!

Will you miss me if I'm away for three weeks then? :wink:
 

Chronos

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My bad, of course I would. The injections of reasonable thought is sorely missed here these days.
 
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The way I explain the photon to myself to account for the fact it has no mass is to bear in mind that it is a wave in an electric field. The properties of an electric field are such that it propagates all disturbances to it at one speed only, c, no faster, no slower and while it can transfer the energy of a disturbance from one location to another, no mass whatever accompanies that transference, just energy. The field is real, but its reality is limited, somehow, to the function of a potential direction for the travel of its waves. The photon has no mass because the medium that carries it, the electric field, has no mass. The photon is the energy of a small, intense disturbance to the position of the electron, traveling away from the electron via its electric field, at the only speed the field is capable of propagating such disturbances.
 

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