Has it been proved that Light does not have a mass

[Astrosag]

I'm currently in an astronomy class and a friend and I asked the question what is there to say that light doesn't have a mass? The professor said she'd get back to us, but hasn't yet. So I'm asking you folks this...what conclusive evidence is there that proves that light doens't have mass...has it been proved? We suspect that there is a possibilty that light has a very very very very small mass, but nonetheless a mass. Of course, we're just college students...so we were hoping someone with more knowledge on the matter could help us. Thanks!

 

[newtonian]

astrosaq - Bedtime for me so this will be brief, and I hope to get back to you.<br /><br />First, you posted:<br /><br />we were hoping someone with more knowledge on the matter could help us.<br /><br />Well, if light has mass, then this would be knowledge on the matter! <br /><br />Otherwise, you are looking for knowledge on the energy!<br /><br />For now, no matter can reach the speed of light according to the theory of relativity.<br /><br />If that statement is correct, then light cannot be matter.<br /><br />Tomorrow night I hope to shed more light on the matter!

 

[newtonian]

astrosag - It turns out to be quite complex.<br /><br />Light can act as a particle (photon) or a wave (part of the electromagnetic spectrum.<br /><br />Electrons also have a wavelength.<br /><br />Evidence indicates both electrons and photons are quantized, as in quantum theory.<br /><br />Try researching the particle theory of light.<br /><br />It explains the absorption and emission of light, while the experimentally observed details cannot be explained by the electromagnetic theory.<br /><br />This involves the discovery of Planck's constant in a formula which gives the quanta of energy - or rather, the energy of the particle of light, depending on the frequency.<br /><br />I.e. Frequency multiplied by Planck's constant.<br /><br />So, can a partilce not have a mass - like a neutrino or graviton?

 

[newtonian]

astrosag - OK, I guess my love for science is stronger than my desire to sleep, so here goes:<br /><br />This is from the June, 2003 issue of Scientific American in an article concerning The Dawn of Physics beyond the Standard Model:<br /><br />The Standard Model describes three of<br />the four known forces: electromagnetism, the weak force (which is<br />involved in the formation of the chemical elements) and the strong force<br />FORCE CARRIERS (BOSONS)<br />(which holds protons, neutrons and nuclei together). The forces are<br />mediated by force particles: photons for electromagnetism, the W and Z<br />bosons for the weak force, and gluons for the strong force. For gravity,<br />gravitons are postulated, but the Standard Model does not include<br />gravity. The Standard Model partially unifies the electromagnetic and<br />weak forces?they are facets of one ?electroweak? force at high energies<br />or, equivalently, at distances smaller than the diameter of protons.<br />One of the greatest successes of the Standard Model is that the<br />forms of the forces?the detailed structure of the equations describing<br />them?are largely determined by general principles embodied in the<br />theory rather than being chosen in an ad hoc fashion to match a<br />collection of empirical data. For electromagnetism, for example, the<br />validity of relativistic quantum field theory (on which the Standard<br />Model is based) and the existence of the electron imply that the photon<br />must also exist and interact in the way that it does?we finally<br />understand light. Similar arguments predicted the existence and<br />properties, later confirmed, of gluons and the W and Z particles.<br /><br />Sorry for the formatting problem.<br /><br />OK, the specific math proves the standard model which states that the photon is a force carrier with no mass.<br /><br />The article adds some details as to experiments confirming the standard model:<br /><br />A Permanent Edifice<br />SIMILARLY, THE STANDARD MODEL is here

 

[vogon13]

No, it has the energy equivalent mass and therefore travels at exactly the speed of light and as we have seen beat to death around here, would have infinite mass if it had any.<br /><br />However,<br /><br />I am aware Heisenbergs uncertainty principle relates to energy and position. How certain is a determination of mass and/or masslessness????<br /><br /><br /><br />Go not to the Elves for counsel, for they shall say both yes and no.<br />J.R.R. Tolkien <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>

 

[alkalin]

That we cannot yet ‘prove’ that light has mass indicates our ability to measure it. When a photon leaves an atom, you might think we could just measure the different mass before and after on the atom. But not if the mass we are talking about is in the noise of the experiment and therefore cannot be repeated accurately. <br /><br />So if someone announced that they ‘measured’ the mass of the photon, they could have their reputation damaged in our current review system, unless they had a way of doing it that far exceeeds sensitivities we currently have in these types of experiments.<br /><br />However, there are ‘photon’ experiments that clearly show that photons do produce ‘mass’ effects, such as pushing around very small objects on the beams of focused lasers.<br /><br />Such things as photon sails are not possible if the photon were strictly a wave. Light actually drives away atoms and very small particles from the sun. Just look at a comet?<br />

 

[astrophoto]

And gravitational lensing and bending of light over supermassive objects in space. 'Light' has to have a mass component, or we do not yet really understand gravity.

 

[Astrosag]

Making some sense now. THank you all!

 

[newtonian]

Steve - I agree with you.<br /><br />Though you clearly do not agree with me.

 

[newtonian]

alkalin -Good post, good point.<br /><br /> I have not actually located experimental proof that a photon has zero mass.<br /><br />I agree it is hard to prove if the mass were so small as to be undetectable by current scientific means.<br />However, as I posted earlier, Scientific American confirms the Standard Model is strong on photons not having mass.<br /><br />The same article, however, did show areas where the standard model is weak.<br />And notes the search is on for the Higgs boson.

 

[newtonian]

astrosaq - Please let us know what your astronomy professor comes back with.<br /><br />Remember the controversy over whether the neutrino has mass?

 

[Astrosag]

Will do!

 

[vogon13]

How identical (mass-wise) would two protons be? Exactly? Within the limits of measurement error? Is there some significant unaccountable quantum weirdness conceivably going on with these particles?<br /><br />It just feels like you're on the edge of something significant...... <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>

 

[newtonian]

vogon13- Did you mean photons or protons?<br /><br />Interesting that both have tons.<br /><br />Talk about making light of a heavy subject!

 

[Saiph]

here's a few things that go for the "massless" explaination:<br /><br />1) They do not fall on earth at the rate of other objects (with an acceleration of 9.8 m/s^2, or ~4 meter fall in the first second).<br /><br />2) They do not collide with, or interact with eachother in any permanent fashion (wave interference only) when two beams collide. If they had mass, they have a size, and as such they should collide and cause dispersion effects.<br /><br />3) The description of propagating electromagnetic waves, as described by maxwell's equations, give a perfect accounting of their behavior in the wave sense (indeed Special relativity can be derived from them!). <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[vogon13]

Yes, protons. Sorry for lack of clarity. Still think there is something down this chain of thought that is really profound, just can't get enough brain lobe wrapped around idea. <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>

 

[newtonian]

vogon13 - perhaps. <br /><br />Why can't quarks exist alone? <br /><br />Why are baryons (neutrons, protons, Lambda, Sigma, etc.) always white by combining red, blue and green quarks? As in the gauge theory of the strong nuclear force; i.e the theory called quantum chromodynamics or QCD for short?<br /><br />Color interactions can make the strong force stronger- and your point is well taken since a measurable increase in energy could be a result of a non-measurable change in mass.<br /><br />I do not know if color interactions can have a slight effect on mass.<br /><br />Ok, to review some basics:<br /><br />Protons and neutrons have almost the same mass.<br /><br />In radioactive decay, specifically beta decay, a neutron changes into a proton and emits an electron and a neutrino.<br /><br />Another form of beta radioactivity involves a proton transmuting into a neutron, but emitting a positron instead of an electron. A positron is an anti-electron.<br /><br />Proton mass: 1.673 x 10^-27 kg = 1.0076 amu (atomic mass unit)<br />Neutron mass: 1.675 x 10-27 kg = 1.0090 amu<br /><br />In the formula e=mc^2, the energy equivalent of one atomic mass unit = 931 million electron volts (MeV).<br /><br />Proton mass = 938.3 MeV<br />Neutron mass = 939.6 MeV<br /><br />The older liquid drop model of the nucleus, by Bohr and Wheeler, does not account for the spin of protons and electrons, so a more recent model: the shell model, does.<br /><br />However, the shell model fails to account for non-spherical electric charges in many nuclei. Therefore an even more recent model known as the collective model combines the best features of the shell and liquid drop models.<br /><br />As of 1991 physicists had not settled on a theoretical model that applies to all nuclei.<br /><br />Accelerator creating by collisions creating exotic isotopes that are spinning very rapidly and are greatly deformed could help determine a more correct model.<br /><br />Protons in hydrogen nuclei are used in NMR imaging due to the magnet

 

[vogon13]

I think I'm back to the irreducible quantum weirdness of everything theory, again. All my forays into this endeavor seem to wind up with me confused and having nagging feeling something major is just out of perceptual range.<br /><br />And as experience has bitterly shown me in the past, sometimes those "aha!" moments turn out to be about as significant as proving 1+0=1. <br /><br />I hate letting me down. <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>

 

[newtonian]

vogon13 - Now you lost me!<br /><br />Well, physicists know there is something major that is out of perceptual range.<br /><br />It is called dark energy.<br /><br />My hope is that someday we will be able to detect dark energy and have dark energy telescopes that will allow us to see beyond our light cone, aka visibility horizon.<br />There is probably allot more we do not know that what we do know.<br /><br />So it is good to keep an open mind, even think outside the box, until things are actually proven.