A simple Q. but not a simple A,,
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From: Timo Nieminen on 28 Dec 2009 01:15 On Dec 27, 9:42 am, Spencer Spindrift <spencerspindr...(a)btinternet.com> wrote: > Q.: How is it that a photon has momentum but no mass? > Or in other words how does light carry energy? > As far as I know momentum is a property of moving or spinning > mass. > A photon cannot have mass or it would be infinite at C.. Consider ripples moving across a pond; they can transfer energy from an object producing the ripples to a distant floating object. How does a ripple carry energy from point A to point B, without carrying mass from point A to point B? More generally, a charged particle being able to exert a force on a distant object means that electromagnetic fields carry momentum. SInce an EM field or wave can carry momentum, a photon can carry momentum. Asking exactly why an EM field can carry momentum or carry energy is pretty much asking why EM forces exist. We don't know why. What we do know is that momentum is not just a property of moving mass - it's more generally a side-effect of moving energy. This is easiest to get to these days as a relativistic effect; just consider Lorentz transformation of an energy-momentum 4-vector. Zero mass means that the magnitude of this 4-vector is zero. (It's a pre-relativistic result, shown by Umov c. 1874 on thermodynamic considerations.)
From: Y.Porat on 28 Dec 2009 05:40 On Dec 27, 1:59 am, Sam Wormley <sworml...(a)gmail.com> wrote: > On 12/26/09 5:42 PM, Spencer Spindrift wrote: > > > Q.: How is it that a photon has momentum but no mass? > >     Or in other words how does light carry energy? > >     As far as I know momentum is a property of moving or spinning > > mass. > >     A photon cannot have mass or it would be infinite at C.. > > > A.; ??? > >   Some properties of photons based on measurements >   For inertial observers, photons propagate at c > >   From the quantum mechanical perspective > >    1. photons are emitted (by charged particles) >    2. photons propagate at c >    3. photons are absorbed (by charged particles) > >   Photon momentum >    p = hν/c = h/λ > >   Photon Energy >    E = hν > >   Particle Chart - Standard Model >    http://www.astro.wisc.edu/~heroux/images/Particle_chart.jpg > >   Conservation of momentum holds. One way to measure photon >   momentum is to it to measure the change in momentum of what >   absorbs or emits a photon. ------------------- the Planck constant HAS MASS !! got it parrot orchestra conductor !! so go parrot your 'partitura' Y.P -----------------
From: Ste on 28 Dec 2009 06:44 On 28 Dec, 07:44, "Y.Porat" <y.y.po...(a)gmail.com> wrote: > > THE PHOTON HAS MASS !! Of course the photon has mass. All energy has mass.
From: Inertial on 28 Dec 2009 07:04 "Y.Porat" <y.y.porat(a)gmail.com> wrote in message news:f443926e-9fb3-4d6a-9c85-cae0fe2bfe63(a)a32g2000yqm.googlegroups.com... > On Dec 27, 1:59 am, Sam Wormley <sworml...(a)gmail.com> wrote: >> On 12/26/09 5:42 PM, Spencer Spindrift wrote: >> >> > Q.: How is it that a photon has momentum but no mass? >> > Or in other words how does light carry energy? >> > As far as I know momentum is a property of moving or spinning >> > mass. >> > A photon cannot have mass or it would be infinite at C.. >> >> > A.; ??? >> >> Some properties of photons based on measurements >> For inertial observers, photons propagate at c >> >> From the quantum mechanical perspective >> >> 1. photons are emitted (by charged particles) >> 2. photons propagate at c >> 3. photons are absorbed (by charged particles) >> >> Photon momentum >> p = hν/c = h/λ >> >> Photon Energy >> E = hν >> >> Particle Chart - Standard Model >> http://www.astro.wisc.edu/~heroux/images/Particle_chart.jpg >> >> Conservation of momentum holds. One way to measure photon >> momentum is to it to measure the change in momentum of what >> absorbs or emits a photon. > > ------------------- > the Planck constant HAS MASS !! No .. it has DIMENSIONS of mass. It doesn't HAVE mass .. it would need to be an actual physical entity to have mass. All it is is a numerical relationship between energy and frequency (and occurs in a number of formulas) .. the dimensions of it are simply what is required to make dimensional analysis work for the formula that expresses that proportionality. > got it parrot orchestra conductor !! Clearly you don't, and instead think that 'h' having dimensions of mass (among others) is somehow significant, and that saying it somehow acts like a magical incantation to refute the statements he made. Odd.
From: Y.Porat on 28 Dec 2009 07:16
On Dec 28, 1:44 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 28 Dec, 07:44, "Y.Porat" <y.y.po...(a)gmail.com> wrote: > > > > > THE PHOTON HAS MASS !! > > Of course the photon has mass. All energy has mass. ---------------- good for you! just tell it to all idiotic parrots energy is mass in motion!! exactly as in macrocosm !!! not to mention that mass is in the dimensions of energy !! ATB Y.Porat ----------------------- |