Can matter be completely converted to energy as suggested by E=mc2?

[Frame Dragger]

Well, if light is traveling through a medium, it seems to me that a photon would keep either "bouncing off" or getting absorbed by atoms. So, if photons always travel at c, why do mediums slow
light down?

OK, gotcha. You're talking about the absorbtion and radiation of photons as they propogate through a medium. Here, this might be some interesting reading of a special case that highlights the general rule. http://www.news.harvard.edu/gazette/2001/01.24/01-stoplight.html


EDIt: Remember, the photon is the quanta, not of light, but of the EM spectrum INCLUDING light.

 

[Char. Limit]

Nice... they stopped light.

So... does light take longer to be absorbed and radiated at extremely low temperatures? But that doesn't explain why the light at a right angle will stop light...

 

[Mentz114]

When is a photon a gauge boson ?

Virtual photons
The electron and nucleon interact by the electromagnetic force, the carrier of this is the virtual photon as has different properties to ordinary photons. Take for example two electrons. These repel each other due to the electromagnetic force, we say that there is a mediator or exchange particle which is transferred between them, the photon.

Extract from http://www.physics.ox.ac.uk/documents/pUS/dIS/virtual_photon.htm ( my bold ).

Also see 100's of other references.

 

[atyy]

When is a photon a gauge boson ?


Extract from http://www.physics.ox.ac.uk/documents/pUS/dIS/virtual_photon.htm ( my bold ).

Also see 100's of other references.

Just to clarify, are you saying a photon is a gauge boson only when it's a virtual photon?

 

[jtbell]

So, if photons always travel at c, why do mediums slow
light down?

There's an entry about this in the FAQ at the top of the General Physics forum, down the hall...

 

[Al68]

If photons always travel at c, why does light get slower through a medium (and don't tell me it doesn't, I've seen rainbows)?

Even if the photon is bouncing off things, its velocity shouldn't change, because it's massless...

The speed of a photon is c, the speed of light propagation isn't c except in the special case where the photon detected is the same exact photon emitted, as in a perfect vacuum.

In the case of a rainbow, the photon reaching your eye isn't the same photon that left the sun. It was absorbed and re-emitted many times, with a delay in between each time. This is true of all transparent mediums to varying extents, hence the different speed of propagation for light in different mediums, and for different wavelengths.

 

[Char. Limit]

I see...

I'm trying to think of another photon question...

 

[DanRay]

Energy is a property of a photon, just as momentum, wavelength and frequency are properties. It is just as incorrect to say that a photon is energy, as it is to say that a photon is momentum, or a photon is wavelength, etc.

I think laymen and beginning students get led to this idea by the frequent of "pure energy" in science fiction. There is no such thing as "pure energy." Energy is always a property of something.

I am a layman for sure (67 year old retiree) and maybe that means I'm just too uninformed to even be in this discussion, or maybe it also could mean that I tend to think outside the box. It is not that I get my ideas from Science Fiction. My idea of "pure energy" comes from my understanding or misunderstanding of what E=mc² means. I have read in many places accurate (or maybe speculative) statements about how much energy could be expected from a given mass if it were all converted to energy. But I am also aware that even an atomic bomb releases only a tiny portion of that amount a good deal of which is spewed out as photons along with superheated radioactive garbage of not just what was the bomb itself but everything that was in the immediate vicinity of the blast. So are you saying there is no possibility of complete conversion of matter to energy as the most famous equation ever seems to indicate to me.

By the way I used to be an avid Science Fiction reader from the mid fifties until around the early seventies. I do not like "Science Fiction" that includes constant wars with aliens and very little about science or thought provoking content. What I read today and have always read is things like Scientific American (Subscriber since my high school days) Science, Astronomy and Science news. My favorite SF author is still Clifford Simak whose sense of humor always made me lol as we say today.

 

[Frame Dragger]

[/B]

I am a layman for sure (67 year old retiree) and maybe that means I'm just too uninformed to even be in this discussion, or maybe it also could mean that I tend to think outside the box. It is not that I get my ideas from Science Fiction. My idea of "pure energy" comes from my understanding or misunderstanding of what E=mc² means. I have read in many places accurate (or maybe speculative) statements about how much energy could be expected from a given mass if it were all converted to energy. But I am also aware that even an atomic bomb releases only a tiny portion of that amount a good deal of which is spewed out as photons along with superheated radioactive garbage of not just what was the bomb itself but everything that was in the immediate vicinity of the blast. So are you saying there is no possibility of complete conversion of matter to energy as the most famous equation ever seems to indicate to me.

By the way I used to be an avid Science Fiction reader from the mid fifties until around the early seventies. I do not like "Science Fiction" that includes constant wars with aliens and very little about science or thought provoking content. What I read today and have always read is things like Scientific American (Subscriber since my high school days) Science, Astronomy and Science news. My favorite SF author is still Clifford Simak whose sense of humor always made me lol as we say today.

No known mechanism exists to convert matter into undifferentiated energy. If a particle annihilates with its antiparticle, you'll have a complete conversion of matter to energy, but it's not "pure energy" in some general potential state. You have photons, neutrinos, etc... that may carry away the energy with a definite potential.

EDIT: For clarity: If I took an a fictional kilogram of anti-hydrogen, and hydrogen and let them annihilate, what would happen? I'm not talking about the particles involved, but in a general sense; there would be an explosion. There would be a conversion of matter to energy, but not some nebulous cloud. Kinetic Energy would be blowing me to bits (along with everything around me), Thermal Energy would be roasting... who knows how large an area. You get the idea.