# Light and space-time

1. Aug 28, 2013

### Akaisora

Is there a reason why light ( electromagnetic waves) is the only thing that can move that fast through space-time? I understand that light doesn't have mass and it is affected by the geometry of space-time, but could there be a specific reason?

2. Aug 28, 2013

### PAllen

Light isn't the only thing that moves that fast. Gravitational waves move at the same speed. If neutrinos were massless as once thought, they would move at this speed. The speed c is the speed of anything without rest mass, and also, the limiting speed of massive particles.

3. Aug 28, 2013

### Akaisora

Can this be related to the higgs field?

4. Aug 28, 2013

### ZapperZ

Staff Emeritus
Not it can't, because the Higgs field does not couple to light.

Zz.

5. Aug 28, 2013

### Naty1

likely there is, but we don't know it. So far physics mostly describes WHAT happens rather 'WHY". A lot of the Standard Model of particle physics [which describes particles and their interactions and characteristics] is based on experimentally measured observations...like zero mass for a photon, it's speed in a vacuum, the mass and charge of an electron, and many other key ingredients. The theories that have been developed fit these observations.

It seems that everything [ forces, particles, space and time, energy, etc] were once 'unified' [existed as a single entity] at the time of the big bang...at the start of our universe. Why the precise characteristics we observe around us actually appeared is still a mystery. For more on these ideas you can check out "fine tuned universe" and 'spontaneous symmetry breaking'.

Here is an example of modeling...How the Higgs mechanism is stuck on to the Standard Model:

http://en.wikipedia.org/wiki/Spontaneous_symmetry_breaking#Higgs_mechanism

So when Zapper posted :
it means that Higgs field does not change the characteristic of light...it has no direct affect on light, but does certain bosons.

6. Aug 28, 2013

### audioloop

read this, at the end, photon can have some mass

http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.021801
"experiments with electric and magnetic fields constrain the mass to less than 10-54 kg"

it would be a possible upper limit.

.

7. Aug 28, 2013

### ZapperZ

Staff Emeritus
Incorrect. That says nothing that it has or can have mass. It is just that up to that limit, there is none detected.

Zz.

8. Aug 28, 2013

### rbj

my spin is that the speed of any ostensibly "instantaneous" interaction (EM, gravity, strong nuclear force) is this same $c$.

so imagine that you're holding a large negative charge and i'm holding a large positive charge and we're restricting the motion along the axis connecting you and me but not along the other two. if i move my charge up a meter, your charge will follow it up. if i move mine to my right, your charge follows to your left (assuming we are facing each other). but, as observed by a third party who is equidistant from you and me, your charge does not respond instantly, but is delayed be a period of time that is proportional to the distance between us (and that constant of proportionality is $1/c$).

if i were to move my charge back and forth a million times per second, your charge would respond that many times also. i would be a transmitting antenna and you would be a receiving antenna and, at that frequency, you could also tune it in with an AM radio. if it were 100 million times per second, you could tune it in with an FM radio. and if it were 500 trillion times per second, you would see it as a blur of orange.

it would be the same if we were big as gods and both holding planets. any perturbation i make with the planet i am holding will be followed by a response with the planet you are holding. and it's the same constant of proportionality regarding the delay observed by the third party and the distance separating us.

so rather than thinking of it as the "Speed of Light" or even as the "Speed of EM", i think of it as the speed of all things ostensibly "instantaneous".

9. Aug 28, 2013

### Naty1

nobody claims any of those are 'instantaneous' except for Newtonian physics approximations.

edit: "i think of it as the speed of all things ostensibly "instantaneous".

not entanglement correlations.

10. Aug 28, 2013

### rbj

are entanglement correlations one of the four fundamental interactions?

11. Aug 28, 2013

### bahamagreen

Wikipedia : Photon : Experimental checks on photon mass

"Photons inside superconductors do develop a nonzero effective rest mass..."

12. Aug 29, 2013

### ZapperZ

Staff Emeritus
And electrons inside a heavy fermion ruthenates can have an effective mass more than 200 times its bare mass. What has this proven?

Unless you are willing to go out on the limb and say that these many-body interactions actually produces a valid covariant mass, this example from photon inside a superconductor has no relevance here.

Zz.

13. Aug 29, 2013

### Naty1

A bit of underlying detail on Zapper's post:

http://en.wikipedia.org/wiki/Effective_mass_(solid-state_physics [Broken])

edit: In other words, particle characteristics ARE affected by their environment.

Last edited by a moderator: May 6, 2017
14. Aug 29, 2013

### Staff: Mentor

No. They aren't an interaction at all, they're correlations. It's tempting to assume that the correlations are caused by something happening between the entangled particles, but this assumption is both deeply problematic and not required by the formalism of quantum mechanics.

15. Aug 31, 2013

### curious bishal

As far as I have understood,light is the fastest thing in universe. But the most important thing is that it is only in the sense of our available technology and science. Scientists had already mentioned that, during the big bang, initially matter travelled and scattered at a great speed; even greater than the speed of light.
You can consider gravitational force as an example. Ligt takes around 8 minutes to reach us from the sun. If you suddenly remove the sun aside, will it take 8 minutes for the gravitational changes to take effect on the earth?
So the things,whatsoever that travels at higher speed than light are yet to discover and I m pretty sure that one day it will come out.

16. Sep 1, 2013

### audioloop

interesting.
thanks for the clarification.

------
another possible upper bound, studies of galactic magnetic fields suggest a much better limit of less than 3 × 10−27 eV.

.

17. Sep 1, 2013

### Staff: Mentor

Yes, this is due to the expansion of space, which does not have a speed limit. There are galaxies right now that are receding away from us at many many times the speed of light. But motion through local space IS subject to a maximum speed limit, c.

18. Nov 3, 2013

### kimster

i also think of that an i get ridiculed about that. light is made of particles and those particles are traveling the speed of light. those particles are traveling the speed of light and they have a limited mass. einstein said that in order to travel faster then light you would have to have infinite energy and an infinite mass.

19. Nov 3, 2013

### Staff: Mentor

Not just limited mass, 0 mass. Mass (aka invariant mass) is given by:
$m^2 c^2 = E^2/c^2 - p^2$

Since photons have $E=pc$ you get m=0.