photon mass

[misterxy]

based on E=MC^2, any object with mass is not able to reach speed beyond the speed of light. photon is traveling at light speed, therefore photon has no mass. if so, how does photon have energy? since mass increases to an extremely large amount when the mass approaches the speed of light. Why can we say that photon has extremely large mass(vs. saying that photon has no mass)? I think that I am confused here. Please educate me. Thank you.<br /><br />---rs

 

[control_group]

No object, with or without mass, can reach beyond the speed of light*. One way to look at it is that the reason photons travel at the speed of light is because they have no mass.<br /><br />To the heart of your question, though: mass and energy are equivalent in a sense, but that doesn't mean something has to have mass to have energy. Photons have no mass, and it's not correct to say they "have" energy, either - they <i>are</i> energy. No one, to my knowledge, claims that photons have very large mass.<br /><br />Basically, I think the hangup is that you seem to be saying that you can't have energy without mass, which is false. E=mc^2 states that energy and mass are interchangeable in the sense that mass can be converted into energy (at the ratio expressed by E=mc^2), and energy into mass. This in no way means that energy has mass like matter does, nor does matter necessarily have energy.<br /><br />To sum up:<br />Photons are massless particles.<br />Photons are energy (as opposed to having energy)<br />It is possible to have energy without mass<br />It is possible to have mass without energy<br />Mass and energy can be converted into each other at the ratio expressed by E=mc^2.<br /><br />*Before why06 jumps down my throat for this one: yes, I recognize that, theoretically, nothing in our current understanding precludes the existence of tachyons. However, since there's no evidence of their existence, I didn't see the need to overly complicate the post.

 

[vogon13]

Energy isn't mass.<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[heyscottie]

Another way to look at it is that photons have no *rest* mass. The fact that they travel at the speed of light from any frame of reference means that we never get to measure a photon at rest, but there you have it.<br /><br />Its energetic properties give it momentum, or what might be termed inertial mass, but it is indeed a massless particle, as anything that travels at c must be.

 

[lukman]

check this out for explanation:<br /><br />http://en.wikipedia.org/wiki/Photon<br /> <div class="Discussion_UserSignature"> </div>

 

[alkalin]

Misterxy,<br /><br />What you ask is not going to resolve your notions of common sense because those notions are based on certain relativistic math equations that do not necessarily represent common sense at or near the speed of light.<br /><br />I would suggest you explore Lorentz relativity that may make more sense. There is no proof whatsoever that mass and energy are equivalent at the speed of light or that you have to have one or the other. But the speed of light is fixed, but not the speed of mass. I’m rather sure some here will object to this remark.<br />

 

[misterxy]

Thank you all for your responses. OK, here is what I think from Einstein's E=mc^2:<br /><br />Everything follows this claim (or law). At least all experiments that have done so far support above equation. Therefore it is *probably* safe to say, the only "thing" that does not follow this law is light (or photons) itself. Can I say this? I guess this is what my confusion is. Then think about it, I think it makes sense. After all, light is a 'mass' collection of photons; And the speed of light is the absolute reference of all others. As far as where the photon energy (or photon is energy) comes from, I am not sure. Maybe God has to play a role here. However, can God create another equally powerful or even more powerful God? I am not sure. It may not be a good analogy, but.. here is the summary:<br /><br />1. E and m are two manifestations of the same "thing". E and m can be converted to each other thru a factor: c^2 (speed of light squared).<br />2. When an object is accelerated to a speed as close as to the speed of light, its m grows (or becomes more dense) to infinite as infinite E is required.<br />3. No object can travel faster than the speed of light.<br />4. Everything but, the speed of light, is relative. Time, length, mass, etc. all are relative (changeable); only the speed of light is absolute, regardless where you look at it or measure it.<br />5. Photon (energy), as a special object, which has no 'rest' mass, always travels, at high speed unless it is absorbed (damaged) and then this energy is *quickly* (how quick? don't know) converted to some other type of energy and may be released.<br />6. Since the speed of light, where photons are, is the only absolute reference as we know, photon does not have "rules" to "restrict" itself. Is this the right way to say it?<br /><br />Thank you.<br /><br />---rs<br /><br /><br /><br />

 

[control_group]

Most of what you say is, as far as I can tell, correct, except for photons not following E=mc^2, which they do. Photons can be (and have been, if I recall correctly) converted into mass at the correct ratio.<br /><br />Part of the problem is thinking that photons "have" energy that "comes from" somewhere; neither is the case. Photons don't "have" energy, they <b>are</b> energy, in the same way that a neutron doesn't "have" matter, it <b>is</b> matter. I think you're understanding this, though, when you ask where photons come from,and your answer is correct. They come from wherever all the other stuff that makes up our universe came from. For the purposes of looking out at stuff right now, though, they just are; they're a fundamental property of the unvierse, as it were.<br /><br />In one sense, yes, E and m are the same "thing," but don't overwhelm yourself with this. They're the same thing insofar as they can be interconverted, but they are not manifestations of some more fundamental substance or property, they just are.<br /><br />Regarding accleration resulting in an increased m, I recently had this question answered for me in another thread: http://uplink.space.com/showflat.php?Cat=&Board=sciastro&Number=660881&page=1&view=collapsed&sb=5&o=0&fpart=<br /><br />What it comes down to is that the m which is commonly referred to is rest mass, and this is not what increases with acceleration. Rather, it is the relativistic mass or inertial mass that increases. One way to look at it is that it isn't the mass that increases, it's the resistance to acceleration.<br /><br />I'm not sure what you mean when you say that photons don't have rules to restrict them. Photons obey the speed of light limit (obviously, since they are light and therefore define its speed), they follow the curvature of s

 

[R1]

Doesn't a photon actually have a rest mass of 1? <div class="Discussion_UserSignature"> </div>

 

[R1]

I know in the examples the photon was not stopped, but if a photon has a rest mass value of 1<br />does that mean a black hole gains mass by not letting go of a lot of light? <div class="Discussion_UserSignature"> </div>

 

[R1]

sorry this is more like for the space science department<br /> <div class="Discussion_UserSignature"> </div>

 

[heyscottie]

No, a photon has rest mass of zero. Anything with rest mass cannot move at the speed of light. Anything with no rest mass MUST move a the speed of light. (According to current models, at least.)

 

[R1]

I'm sorry you are very right.<br />I have no idea what I was thinking about.<br />The closest possible thing is that a photon has a spin value of 1.<br /><br />thanks for pointing that out <img src="/images/icons/smile.gif" /><br /><br /> <div class="Discussion_UserSignature"> </div>