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/sci/ - Science & Math

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4640737 No.4640737 [Reply] [Original]

Does light have a mass?
What is the mass of light?

>> No.4640738

no
nothing

>> No.4640743

>>4640738
Why is it affected by gravity then?

>> No.4640745

>>4640743
It isn't. Light travels in a strait line through space time. It's your fault for viewing space time as curved.

>> No.4640746

Light has to have mass. Solar sails wouldn't work otherwise. Right?

>> No.4640744

>>4640743
gravity effects space, which light is travelling through

>> No.4640747

>>4640743

Its not, space is warped by gravity which subsequentially alters lights spacetime trajectory.

>> No.4640751

>>4640737
Photons are thought of as having no mass in application, but in actuality, that's up for debate.

http://en.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass

>> No.4640752

How does light have momentum then (according to DeBroglie)?

>> No.4640755

Black holes suck all the light around them, why is that so if light has no mass. Would it not be affected by black hole's gravity if it didn't have any mass?

>> No.4640758

>>4640755
Black holes warp space

>> No.4640764

>>4640746
http://en.wikipedia.org/wiki/Radiation_pressure

>> No.4640766

>>4640755

A blackholes event horizon warps spacetime to the point of it curving back on itself. Light can't escape because its spacetime trajectory is curved continuously back into the blackhole.

>> No.4640772

In the Standard Model, photons have no rest mass.

>> No.4640780

>>4640766
Wow, someone actually does physics? I'm surprised you didn't mention light cones.

>> No.4640808

Here we go OP:

Light has no mass. (Well, not in the conventional sense at least. You could say it has "relativistic mass," defined as <span class="math">m_r=E/c^2[/spoiler], but relativistic mass is pretty much a meaningless, useless quantity. Light has no invariant (rest) mass, which is what matters.)

Light has momentum by virtue of the fact that it has energy. From special relativity, you get the following:

<span class="math">E^2=m^2c^4+p^2c^2[/spoiler]

Set m=0 and you get E=pc. The relationship isn't quite as simple in curved spacetime, but the essence is the same.

The reason light is effected by gravity is because the light is simply following the straightest possible line through a curved spacetime. Energy and momentum curve spacetime, and objects (including photons) abide by a more general Newton's first law through this curved spacetime.

>> No.4640842

>>4640764
>>4640766
>>4640808
Cheers!

>> No.4640845

>>4640808
SHIIiiiiIIIiiIiiiiiIIiTTTTT NIGGAAAAA

>> No.4640849

>>4640746
Light has momentum, but no mass.

>> No.4640876

OP, that picture is adorable.