What makes light travel?

Question

how does a photon travel, that is, achieve light speed?

Answer 1

Go review maxwell's equations.

A changing B-field induces an E-field.  A changing E-field induces a B-field.  So if you shake a charge, it starts a wave that travels at light speed.  You can derive the wave equation (and the speed c) from maxwell's equations.

Now if you want to know about a photon, maybe you wanted a quantum answer, not the classical answer.  But it turns out to be the same thing.  The field equation for the photon (the Proca equation) gives you maxwell's equations.  And any massless particle HAS to travel at light speed.

Answer 2

Rage3D Discussion Area > Off-Topic Forum > Off Topic Lounge > What propels light?

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_leech_

Oct 30, 2003, 12:58 PM

I was just thinking about how it might be almost impossible to make anything move at the speed of light (at least to my knowledge) so - this might sound stupid, or maybe not - what propels light?

:confused:

Oscar1613

Oct 30, 2003, 01:03 PM

nothing "propels" light... its merely the propagation of a magnetic and electrical field

Djinn

Oct 30, 2003, 01:05 PM

Photons have no mass. Therefore, they don't require an external force for propulsion.

VW_Factor

Oct 30, 2003, 01:09 PM

If anyone truely found an answer to such a question, it would be the late Nikola Tesla.. Perhaps some searching around for some of his works would reveal an answer.

Clockwork

Oct 30, 2003, 01:10 PM

Originally posted by Oscar1613

nothing "propels" light... its merely the propagation of a magnetic and electrical field

Indeed.

http://science.howstuffworks.com/light.h...

ThereIsASpoon

Oct 30, 2003, 01:16 PM

photons have mass, however little it may seem to us.

Djinn

Oct 30, 2003, 01:18 PM

Originally posted by ThereIsASpoon

photons have mass, however little it may seem to us.

As a body with mass approaches the speed of light, its mass increases. When it reaches the speed of light, the mass is infinite.

If photons have mass, then they can't ever travel at the speed of light.

Djinn

Oct 30, 2003, 01:20 PM

Originally posted by VW_Factor

If anyone truely found an answer to such a question, it would be the late Nikola Tesla.. Perhaps some searching around for some of his works would reveal an answer.

Don't get me wrong, Tesla did some remarkable things - including some verified tricks that we haven't been able to repeat to this day. But the guy WAS a whack-job. Classic mad-scientist. He produced at a roughly 70:30 brilliance-to-bullsh*t ratio.

XSBagage

Oct 30, 2003, 02:06 PM

Originally posted by ThereIsASpoon

photons have mass, however little it may seem to us.

You're mixing them up with electrons.

Djinn

Oct 30, 2003, 02:11 PM

Photons do not have mass.

http://imagine.gsfc.nasa.gov/docs/ask_as...

XSBagage

Oct 30, 2003, 02:12 PM

Originally posted by Djinn

Ph

Answer 3

A changing electric field induces a changing magnetic field in the vaccum, and visa verse. This causes the two fields to oscillate back and forth and propagate through space at the speed of light. The equations which describe this dynamics are called Maxwell's equations. This is a macroscopic approximation for more fundamental quantum field equations. As to, "what makes", that's about as deep as it goes if you're talking about physics. Physics stops at fundamental equations, and there really is no "why", if that's what you mean.

Answer 4

It always travels at light speed. It is impossible to accelerate TO light speed, according to normal physics.

How / why does it do it? Good question.