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electromagneticpulse
2004-Jul-24, 06:47 PM
Hey, i was wondering what people thought about photons having a Finite speed without mass. This either implies that there is a limit on Infinity or that a photon has a mass that we currently cant detect.

The biggest "proof" that a photon has mass is that it can be "sucked" into a black hole and gravity is the interaction of matter, something with no matter can't be attracted by gravity because the (theoretical) gravitons have nothing to effect. Also the creation of gravity through electromagnetic radiation into gravaton radiation (http://www.americanantigravity.com/index.shtml the experiments are listed on here with info... blah blah) so either gravity isn't caused by mass in which newtonian physics are wrong. Also the EMg partial seperation of gravity from electromagnetic radiation, nobody can deny that magnetism acts like gravity it even has the same field just magnetism uses the dipolar effect of an electron.

A test for photonic mass can not be performed as the energy needed to be able to get an indetail of what an electron is made up of it is said would take more energy then mars' moon phobos (i think its mars) being completly reacted with antimatter, which would probably decimate the majority of our solar system.

Also a photon can never exist slower then the speed of light because it has no rest mass and it can not have rest mass to reach the speed of light because it would become infinate mass. But light can be slowed down to under 60 miles per hour in some crystaline structures so it must have a rest mass to slow down. so whats wrong the constant speed or a photons mass?

Sorry if i've babbled on but i was wondering what other people thought about photons having mass.

Normandy6644
2004-Jul-24, 06:57 PM
It used to bother me too, but then I realized it was kind of essential to particle physics for it to be massless. It's hard to accept at first, but a photon can have momentum, which in turn gives it energy. Einstein showed that mass isn't the only thing to cause gravity, it's also energy (and a few other things, but those are the important ones). So if a photon has energy, it can be treated to respond to the same gravitational effects that any other object would have.

By the way, welcome to the board!

Omicron Persei 8
2004-Jul-24, 08:56 PM
Also a photon can never exist slower then the speed of light because it has no rest mass and it can not have rest mass to reach the speed of light because it would become infinate mass. But light can be slowed down to under 60 miles per hour in some crystaline structures so it must have a rest mass to slow down. so whats wrong the constant speed or a photons mass?

Sorry if i've babbled on but i was wondering what other people thought about photons having mass.

You have the premise of the experiment wrong. Light never slows below c in those experiments. Photon transmission is always at c. But the propagation times in which this took place can be slowed. That is what they did. They controlled how the supercold atoms (or in another case a crystal) absorbed and reemitted those photons. In essence, light acted like it was traveling that slow but reality the photons weren't what was traveling slower. If you're confused don't worry. A lot of folks were puzzled by such an experiment. But it all came down to quantum mechanics or in this case quantum electrodynamics.

Ut
2004-Jul-25, 12:45 AM
Hrmm. So that's how they did it. I never really understood how they were "slowing down" light. Then again, I never really looked it up, either. I often forget that I have the worlds largest encyclopedia at my fingertips.

Omicron Persei 8
2004-Jul-25, 01:40 AM
Here is some more info if you want it:

http://www.spie.org/app/Publications/magazines/oerarchive/may/may99/cover2.html

although it leaves out the quantum mechanics and sticks to group wave velocities.

CaptainToonces
2004-Jul-25, 10:02 AM
It's hard to accept at first, but a photon can have momentum, which in turn gives it energy. Einstein showed that mass isn't the only thing to cause gravity

Normandy, Einstein also shows us that if something has energy it also has mass, specifically, that energy divided by cē in mass.

Yazdi
2004-Jul-25, 11:59 AM
Well, according to my physics teacher they do. And it's not much of a problem, because they can't move at speeds less than c. And the fact that they move, means that they have energy. ANd if they have energy, they have mass.

Tensor
2004-Jul-25, 01:48 PM
It's hard to accept at first, but a photon can have momentum, which in turn gives it energy. Einstein showed that mass isn't the only thing to cause gravity

Normandy, Einstein also shows us that if something has energy it also has mass, specifically, that energy divided by cē in mass.

Captain, the equation E = mc^2 is only applicable if the object in question is at rest. If it is in motion, as a photon always is, Then he equation becomes E^2 =(mc^2)^2+(pc)^2. And since a photon's energy has been obserserved to equal it's momentum, the mass term has to be zero. I think the problem arises in how physicist and laymen use the term "mass". When physicist use the term, it is the rest mass of the object, not the total energy of the object. While thinking of the total energy as "Relativistic mass" is not really incorrect, its use is outdated based on current terminology.

Tensor
2004-Jul-25, 01:53 PM
Well, according to my physics teacher they do. And it's not much of a problem, because they can't move at speeds less than c. And the fact that they move, means that they have energy. ANd if they have energy, they have mass.

If you teacher wants to claim this, ask him to explain relativistic momentum.

Normandy6644
2004-Jul-25, 04:13 PM
Well, according to my physics teacher they do. And it's not much of a problem, because they can't move at speeds less than c. And the fact that they move, means that they have energy. ANd if they have energy, they have mass.

As Tensor said, the equivalence of mass an energy is for rest mass. The equation he wrote for relativistic energy more accurately describes what's really going on. Photons have momentum (something Einstein showed), but no mass.

electromagneticpulse
2004-Jul-27, 10:39 PM
okay well thanks.
now heres another question,
first would it be possible to slow down a photon using gravity?
if you think so, would it gain rest mass or would it give off its energy in some form?

ZaphodBeeblebrox
2004-Jul-27, 10:53 PM
okay well thanks.
now heres another question,
first would it be possible to slow down a photon using gravity?
if you think so, would it gain rest mass or would it give off its energy in some form?

Actually, what happens to a Photon Coming out of a Gravity Well, is it gives up some of its Energy, to the Gravitational Field.

What this does, is it Red-Shifts the Photon, as it Climbs out.

In Really, Really Steep Gravity Wells, such as Black Holes, the Photon actually Red-Shifts itself, into Non-Existence.

Normandy6644
2004-Jul-28, 12:14 AM
okay well thanks.
now heres another question,
first would it be possible to slow down a photon using gravity?
if you think so, would it gain rest mass or would it give off its energy in some form?

Actually, what happens to a Photon Coming out of a Gravity Well, is it gives up some of its Energy, to the Gravitational Field.

What this does, is it Red-Shifts the Photon, as it Climbs out.

In Really, Really Steep Gravity Wells, such as Black Holes, the Photon actually Red-Shifts itself, into Non-Existence.

I always like to point out (since it's simple) that this comes from the equation E=hf, where E is the energy, h is Planck's constant, and f is the frequency. Lower the energy, then you lower the frequency, and hence redshift the photon, since frequency and wavelength are inversely proportional (c=lambda*f).

bearcub
2004-Jul-28, 01:01 AM
Actually, what happens to a Photon Coming out of a Gravity Well, is it gives up some of its Energy, to the Gravitational Field.

What this does, is it Red-Shifts the Photon, as it Climbs out.

In Really, Really Steep Gravity Wells, such as Black Holes, the Photon actually Red-Shifts itself, into Non-Existence.

Thanks Zaphod. That's actually one of the best (non mathematical) descriptions I've seen for this. I'm slowly screwing up the courage to start learning the math, but this gives a mental picture I can wrap my brain around. =D>

ZaphodBeeblebrox
2004-Jul-28, 01:28 AM
Actually, what happens to a Photon Coming out of a Gravity Well, is it gives up some of its Energy, to the Gravitational Field.

What this does, is it Red-Shifts the Photon, as it Climbs out.

In Really, Really Steep Gravity Wells, such as Black Holes, the Photon actually Red-Shifts itself, into Non-Existence.

Thanks Zaphod. That's actually one of the best (non mathematical) descriptions I've seen for this. I'm slowly screwing up the courage to start learning the math, but this gives a mental picture I can wrap my brain around. =D>

You want a Mental Picture you can Really, Really Wrap your Mind Around?

In his Short Story, "What Continues, and What Fails," David Brin offers an even more Intriguing Possibillity.

If those Red-Shifted Photons come into Contact with another Black Hole, they'll start Blue-Shifting back towards Visible, again!

Theoretically, if you positioned a Recording Device, in between Two Colliding Blach Holes, it is Technically Possible, to Actually "See" these, Very Red, Virtual Photons; as for what would be seen, that's just it, Nobody Really Knows ...

bearcub
2004-Jul-28, 01:41 AM
OK, now my brain's wrapping itself into knots :lol:

I like Brin. I'll have to look around and see if I can find that story.

ZaphodBeeblebrox
2004-Jul-28, 03:13 AM
OK, now my brain's wrapping itself into knots :lol:

I like Brin. I'll have to look around and see if I can find that story.

The best place to find it, is in his Short Story Collection, Otherness, lots of Good Stuff, in there!

http://www.amazon.com/exec/obidos/ASIN/0553295284/qid=1090984398/sr=ka-1/ref=pd_ka_1/002-0758709-0819239

electromagneticpulse
2004-Jul-28, 07:23 AM
oh well there go my hopes of putting photons in the middle of a gummie ball :( hmm maybe plutonium!

how come photons don't react with all matter? we all know that it does react with matter or i wouldn't be seeing what i'm typing.

i hate photons so hard to understand the wave-particle duality and how it all works but guess asking these stupid questions is the way.

okay if i have a window pane of glass and a window pane of aluminium, what part of the aluminium atoms makes it not let an EM wave through or would it just absorbe some of the energy of it and let some pass through (if the EM wave is aimed at a 90° angle)

My dumb question done for another day :D

01101001
2004-Jul-28, 07:56 AM
okay if i have a window pane of glass and a window pane of aluminium, what part of the aluminium atoms makes it not let an EM wave through or would it just absorbe some of the energy of it and let some pass through (if the EM wave is aimed at a 90° angle)
Mostly, it is the organized crystal structure of aluminum that stops the light by reflecting it. Glass has more randomized, amorphic structure, somewhat similar to a liquid. Another big influence on transparency is where the electrons of the matter are and what they can do to photons they meet.

Oh, here's a simple explanation: How Stuff Works (http://science.howstuffworks.com/question404.htm).

For an awesome matter, wonder at how much of your body is opaque or maybe slightly translucent, but your eye cornea, aqueous humor, lens, and vitreous humor are you-stuff that is as transparent as glass.

electromagneticpulse
2004-Jul-28, 08:05 AM
i was lead to believe that glass was a high viscosity liquid, like a snail it'll run but it'll take its time about it :P, i thought it made more sense for it to be a liquid crystal that just doesnt bend the light.

i say we develop see-though steel or something, like spreading that jelly they use for ultra sound on a wall and been able to see through it.... think of the uses!

01101001
2004-Jul-28, 04:43 PM
ii say we develop see-though steel or something
Remember Star Trek IV where Scotty bargained for a load of transparent aluminum (http://www.theverylastpageoftheinternet.com/newclaims/aluminum/transparent_aluminum.htm)?

Oops. That is transparent alumina -- aluminum oxide, a ceramic.

bearcub
2004-Jul-28, 07:04 PM
OK, now my brain's wrapping itself into knots :lol:

I like Brin. I'll have to look around and see if I can find that story.

The best place to find it, is in his Short Story Collection, Otherness, lots of Good Stuff, in there!

http://www.amazon.com/exec/obidos/ASIN/0553295284/qid=1090984398/sr=ka-1/ref=pd_ka_1/002-0758709-0819239
Cha-ching ........... just ordered it (and a few others). Thanks!

electromagneticpulse
2004-Jul-29, 03:37 PM
haha 01101001 where do you think i got the idea from :P
i just hope they dont make a house out of that transparent aluminum... you could see someone going for a number 2 :-?

Wally
2004-Jul-29, 06:41 PM
The biggest "proof" that a photon has mass is that it can be "sucked" into a black hole and gravity is the interaction of matter, something with no matter can't be attracted by gravity because the (theoretical) gravitons have nothing to effect. .

Careful here! Actually, the photon is travelling in a straight line, and is not affected (directly anyways) by a gravity well. Space, on the other hand, is affected, and curves as a result of a massive body (or singularity in the case of a BH). We see light travelling thru this warped space as light "curving" when really it's a straight line (from the photon's perspective).

iantresman
2004-Jul-29, 08:51 PM
Hey, i was wondering ... that a photon has a mass

Doesn't a photon have energy? Doesn't E = m c^2 ?

Regards,
Ian Tresman

iantresman
2004-Jul-29, 08:54 PM
Also a photon can never exist slower then the speed of light

I though light slows down as it moves through glass causing it refract?

Regards,
Ian Tresman

electromagneticpulse
2004-Jul-30, 12:12 AM
yeah thats what i dont get either it cant move slower then the speed of light, the denser an object the slower it moves for example the sun it takes over 10,000 years for it to get out and then another 8 mins i think it is to get to our eyes. I have no clue why it slows down but apparently it just does.

Omicron Persei 8
2004-Jul-30, 12:25 AM
yeah thats what i dont get either it cant move slower then the speed of light, the denser an object the slower it moves for example the sun it takes over 10,000 years for it to get out and then another 8 mins i think it is to get to our eyes. I have no clue why it slows down but apparently it just does.

Classically you are correct, but in reality light isn't thought of as "classic". Quantum electrodynamics states that light interecting with matter is actually photons interacting with electrons. Light's ability to slow down through a material is just apparent. What is really going on is that photons are captured by electrons and spit back out with a bit of momentum shaved off because you have to balance the universal books...hence the effect of refraction. The reason something looks transparent is that the electrons of the material can't match the specific energy or energies of incoming photons. So instead of being able to accept a photon, jump into a different orbital and then drop back into its original orbital and in the process releasing an different energy photon, the electron accepts the photon but can't relate its energy to a specific orbital jump so it releases it but in the process it shaves some momentum of the photons.

So all in all the photons are absorbed and reemitted throughout the material all the while traveling at c. The apparent slowdown is the delay you are seeing is from this absorption/emittance process.

electromagneticpulse
2004-Jul-30, 02:50 PM
Finally i understand it! i knew that electrons jumped to higher energy levels when hit by a photon and the energy is then re-emmited so while its in the physical state of being a photon it travels at c and when it shifts an electron into a higher energy level the photon's energy can't move until its re-emmited. its all so simple now.
Thanks Lrrr, i mean Omicron Persei 8... you got any of those ray guns i could borrow? :D

Omicron Persei 8
2004-Aug-03, 10:42 PM
Thanks Lrrr, i mean Omicron Persei 8... you got any of those ray guns i could borrow? :D

Puny human, that question ANGERS AND CONFUSES ME! ;)

amateurphysicist
2004-Aug-11, 03:11 AM
It used to bother me too, but then I realized it was kind of essential to particle physics for it to be massless. It's hard to accept at first, but a photon can have momentum, which in turn gives it energy. Einstein showed that mass isn't the only thing to cause gravity, it's also energy (and a few other things, but those are the important ones). So if a photon has energy, it can be treated to respond to the same gravitational effects that any other object would have.

By the way, welcome to the board!

I agree: energy/momentum - yes, mass - no.

stryker
2004-Aug-11, 09:42 AM
Careful here! Actually, the photon is travelling in a straight line, and is not affected (directly anyways) by a gravity well. Space, on the other hand, is affected, and curves as a result of a massive body (or singularity in the case of a BH). We see light travelling thru this warped space as light "curving" when really it's a straight line (from the photon's perspective).

Thanks wally.... as a newcomer to physics and very interested in the energy/matter relationship I was about to kick up an old flame on photons having a mass using their travel being warped by a massive energy well.... but your explanation is a very interesting one at that!!!! I'd had a firm believe that light had mass, it had to however you've just thrown that believe into jeopardy :o

I still would like to think photons have mass on a scale we can not detect. I say this because if they dont have mass then we could never hope to travel faster than the speed of light????

(sorry to throw things off topic)