petermartin Posted April 16, 2012 Share Posted April 16, 2012 You tell me, i have my own theory. Link to comment Share on other sites More sharing options...
mathematic Posted April 16, 2012 Share Posted April 16, 2012 You tell me, i have my own theory. Sort of by definition. The speed of light is the speed with which light travels. 1 Link to comment Share on other sites More sharing options...
swansont Posted April 17, 2012 Share Posted April 17, 2012 ! Moderator Note petermartin, please note that any discussion of your theory should take place in the Speculations forum, and is subject to its rules. This is a physics board, and is limited to discussion of accepted physics. There is a speed at which massless particles travel. Photons are massless, so they travel at this speed. Link to comment Share on other sites More sharing options...
questionposter Posted April 17, 2012 Share Posted April 17, 2012 In other words, no one really knows for sure. All we know is that that's just how the universe happens to work. Link to comment Share on other sites More sharing options...
petermartin Posted April 17, 2012 Author Share Posted April 17, 2012 But why? When that photon, be it massless particle or wave, is liberated from an atom why does it race off at the cosmic speed limit? Is there not a mathematical formula for an electromagnetic wave which can be used to calculate the speed at which it propogates through space? Sorry Swansont, only just noticed my 'telling off'! Can you move this to its correct pleace? Link to comment Share on other sites More sharing options...
timo Posted April 17, 2012 Share Posted April 17, 2012 Is there not a mathematical formula for an electromagnetic wave which can be used to calculate the speed at which it propogates through space? Sure is. The dispersion relation (the relation between energy E and momentum p) for the free electromagnetic field is [math]E = pc[/math], which is a simplification of the more general dispersion relation for free fields ([math]E^2 = m^2 c^4 + p^2 c^2[/math]) resulting from a mass-like term that is zero (m=0). From that, you directly get a group and phase velocities [math] \frac{\partial E}{\partial p} = \frac Ep = c[/math] for wave packets of the free electromagnetic field. Link to comment Share on other sites More sharing options...
imatfaal Posted April 17, 2012 Share Posted April 17, 2012 Maxwell's equations will also pop out a speed for Electromagnetic Radiation through vacuum Relation between electricity, magnetism, and the speed of light 1 Link to comment Share on other sites More sharing options...
petermartin Posted April 19, 2012 Author Share Posted April 19, 2012 I agree, (I've always struggled with massless particles having momentum) but are these equasions not back engineered? They certianly explain the relationships but not the reason, that is, they do not explain why the photons leaving your display are so repulsed by the atoms in the LED and so attracted to the atoms in your retina. Go easy on me! Link to comment Share on other sites More sharing options...
Klaynos Posted April 19, 2012 Share Posted April 19, 2012 I agree, (I've always struggled with massless particles having momentum) but are these equasions not back engineered? No, massless particles having momentum can be derived in special relativity. E2=(mc2)2+p2c2 where m is the rest mass, p momentum, E energy and c the speed of light in a vacuum. They certianly explain the relationships but not the reason, that is, they do not explain why the photons leaving your display are so repulsed by the atoms in the LED and so attracted to the atoms in your retina. I think you might be looking for something outside the bounds of science. Science answers how, not why. Maxwell's equations will also pop out a speed for Electromagnetic Radiation through vacuum Relation between electricity, magnetism, and the speed of light This is the answer I would give. But then you just get the question of why are the free space permittivity and permeability the values that they are. We're back to science not answering why but how. Link to comment Share on other sites More sharing options...
petermartin Posted April 19, 2012 Author Share Posted April 19, 2012 Thank you Klaynos, I am looking at understanding something that is outside the current bounds of science, it is something that will change our whole perception of the universe and the way it works. The speed of light question is just the start. Link to comment Share on other sites More sharing options...
timo Posted April 19, 2012 Share Posted April 19, 2012 It's unlikely that your ideas will change any perception other than yours. The "I have the answer" market is rather competitive. 1 Link to comment Share on other sites More sharing options...
petermartin Posted April 19, 2012 Author Share Posted April 19, 2012 Thank you Timo, that told me! Unlikly yes, impossible no. Link to comment Share on other sites More sharing options...
pmb Posted April 30, 2012 Share Posted April 30, 2012 No, massless particles having momentum can be derived in special relativity. E2=(mc2)2+p2c2 Please post such a derivation. Typically such derivations are really identities. Link to comment Share on other sites More sharing options...
elfmotat Posted May 1, 2012 Share Posted May 1, 2012 (edited) Please post such a derivation. Typically such derivations are really identities. Well, typically [math]p_\mu p^\mu \equiv m^2[/math]. Since [math]p^\mu =(E,p^i)[/math] where [math]p^i[/math] is the three-momentum, it's easy to see for a particle with m=0 that [math]E^2=p_i p^i[/math]. So massless particles have momentum by virtue of their energy. Edited May 1, 2012 by elfmotat Link to comment Share on other sites More sharing options...
swansont Posted May 1, 2012 Share Posted May 1, 2012 Please post such a derivation. Typically such derivations are really identities. Take the four-velocity. Multiply by m. Evaluate. Link to comment Share on other sites More sharing options...
elfmotat Posted May 1, 2012 Share Posted May 1, 2012 Take the four-velocity. Multiply by m. Evaluate. The four-velocity of a photon is undefined. Link to comment Share on other sites More sharing options...
swansont Posted May 1, 2012 Share Posted May 1, 2012 The four-velocity of a photon is undefined. And multiplying by their mass doesn't mean much, either. We aren't discussing photons, specifically. As with a few aspects of physics, they are a special case. Link to comment Share on other sites More sharing options...
elfmotat Posted May 1, 2012 Share Posted May 1, 2012 (edited) And multiplying by their mass doesn't mean much, either. We aren't discussing photons, specifically. As with a few aspects of physics, they are a special case. pmb's question was about photons, not 4-momentum in general. Edited May 1, 2012 by elfmotat Link to comment Share on other sites More sharing options...
zapatos Posted May 1, 2012 Share Posted May 1, 2012 (edited) Nevermind. Edited May 1, 2012 by zapatos Link to comment Share on other sites More sharing options...
swansont Posted May 1, 2012 Share Posted May 1, 2012 pmb's question was about photons, not 4-momentum in general. You're right; I misread it. p= E/c is a classical notion from EM waves. It's established in relativity with a discussion of a photon being emitted in a system (a railroad car). Einstein had already established that this would change the mass of the emitter, but this changes the center of mass of the system, which violates conservation of momentum. p=E/c drops out of that discussion. http://farside.ph.utexas.edu/teaching/em/lectures/node90.html Link to comment Share on other sites More sharing options...
imatfaal Posted May 4, 2012 Share Posted May 4, 2012 ! Moderator Note Wucko's theory approaching the question from a new and speculative angle has been split off to speculationshttp://www.scienceforums.net/topic/66209-the-speed-of-light-and-discrete-notions-of-space-and-time/page__view__findpost__p__675852 1 Link to comment Share on other sites More sharing options...
petermartin Posted May 4, 2012 Author Share Posted May 4, 2012 Should you not move mine also? Link to comment Share on other sites More sharing options...
mindless Posted May 4, 2012 Share Posted May 4, 2012 The reason that the speed of light is a constant in relativity is because all observers observe the same spacetime interval (s) when: s = 0 = x^2 + y^2 + z^2 - (ct)^2 suppressing y and z axes this happens when: x = ct ie when x/t = c , ie: when an object is moving at light speed. The explanations in many of the posts above give an idea of why electromagnetic phenomena propagate along a zero spacetime interval. Link to comment Share on other sites More sharing options...
wucko Posted May 5, 2012 Share Posted May 5, 2012 (edited) ! Moderator Note Wucko's theory approaching the question from a new and speculative angle has been split off to speculations http://www.sciencefo...post__p__675852 if i write it again in math or in C++, will you leave it here? Can I suggest an option to mark a post as 'a try on a hypothesis', just to give hypothetical reasoning a chance here and with that a chance to answer real questions by asking better ones? for your inspiration: Edited May 5, 2012 by wucko Link to comment Share on other sites More sharing options...
wucko Posted May 9, 2012 Share Posted May 9, 2012 (edited) I agree, (I've always struggled with massless particles having momentum) but are these equasions not back engineered? They certianly explain the relationships but not the reason, that is, they do not explain why the photons leaving your display are so repulsed by the atoms in the LED and so attracted to the atoms in your retina. Go easy on me! One of the pseudoscientific instances is the confusion of correlation with causality. Physics seems to be biased in the dirrection of confusing causality with correlation. Its an ideology as much as a science. Thats the problem also. Edited May 9, 2012 by wucko Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now