Cosmic uncertainty: Is the speed of light really constant?

New Scientist ^ | 03/01/2017 | Stuart Clark

[SeekAndFind]

The speed of light in a vacuum is the ultimate cosmic speed limit. Just getting close to it causes problems: the weird distortions of Einstein’s relativity kick in, so time slows down, lengths go up, masses balloon and everything you thought was fixed changes. Only things that have no mass in the first place can reach light speed – photons of light being the classic example. Absolutely nothing can exceed this cosmic max.

We have known about the special nature of light speed since an experiment by US physicists Albert Michelson and Edward Morley in the 1880s. They set two beams of light racing off, one parallel and one at right angles to the direction of Earth’s rotation, assuming the different relative motions would mean the light beams would travel at different speeds – only to find the speed was always the same.

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Light’s constant, finite speed is a brake on our ambitions of interstellar colonisation. Our galaxy is 100,000 light years across, and it is more than four years’ light travelling time even to Proxima Centauri, the closest star to the sun and home, possibly, to a habitable planet rather like Earth.

Then again, if the speed of light were infinite, massless particles and the information they carry would move from A to B instantaneously, cause would sit on top of effect and everything would happen at once.

[roadcat]

In the absence of a medium, a photon's energy has nowhere to go.

There is a lot we humans don't know. Is there really an absence of a medium in space? There is a lot of dark matter in space that our scientists can't detect, yet they know it is there. There are electromagnetic connections between stars, planets, and galaxies that we cannot see. These photons travel billions of light years, and it is hard to imagine that they don't interfere with other photons along other paths as they intersect. Yes, space is vast, but there are an almost infinite paths of light everywhere in space, criss-crossing everywhere. I find it hard to believe that these photons don't give up energy bumping into each other or when hitting dark matter, gravity waves or other electromagnetic interference because maybe a medium is everywhere. We may never know the answers.

[John Locke]

Sad to see the New Scientist repeating this historic disinformation. Michaelson and Morley did measure an aether drift. But it was much smaller than they expected, so they considered it due to experimental error (vibration, temperature differences &c) and reported a null result.

No, they should not have done that: clear scientific malpractice. But I guess they wanted the fame they duly acquired. They also abandoned their original plan to repeat the measurement at three-monthly intervals, and let stand their single result.

And now for the bad news. Every experiment that looked for an aether drift - every experiment, I kid you not - actually found one. This includes Sagnac (1913), Michaelson & Gale (1925), and, especially, the numerous experiments of Dayton Miller, from 1906 to 1933.

Details here: http://www.orgonelab.org/miller.htm

After collating many experiments, Miller claimed the Earth had a velocity, relative to the aether, of about 298 km/sec. Today, we claim the Earth has a velocity, relative to the cosmic microwave background radiation, of about 370 km/sec. Plus ca change.

[John Locke]

Light moves more slowly in a gravitational field (as predicted by Einstein). The bending of light then follows from the least time theorem of Heron of Alexandria - light always follows the path that gets it there quickest. But how does it know? I wish I had a least time theorem to get me around Singapore.

[dhs12345]

Isn’t related to the properties of the E and the M in a TEM wave and how the two reinforce/produce each other at a fixed rate which is c?

[SuperLuminal]

Damn straight!

[SpaceBar]

It’s the reciprocal of the square root of the product of the permittivity and permeability of free space. Interestingly, neither of these properties require the existance of the photon and can be measured in the laboratory with modest equipment. Now as the article suggests, that these ‘constants’ aren’t really constant over vast periods of time, then due to things like the wave equation, light would ‘go along for the ride’ and adjust its speed accordingly, presumably over vast expanses of cosmological time. But for our little snapshot, c is for all intents and purposes, rock solid constant as measured from in all inertial reference frames. As an aside, since we don’t know the nature of conciousness and subjective time, and being essentially chemical meat computers, it makes one wonder if we’d even be aware of such a change in c.

[Redcitizen]

Their final words were “We got mooned!”

[Redcitizen]

“Is the speed of light really constant?”

Yes the speed of light is constant. It’s the speed of dark that is inconstant.

[HandyDandy]

"Matter that is stationary goes zero speed through space,....."

Is there any stationary matter?

[John Locke]

Check out a book by George Gamow called Mr Tompkins in Wonderland. It describes an everyday guy who finds himself in a dream world where the speed of light is 30 mph.

It's fantasy, of course, because as you point out, an our-world guy could not exist in that world. And that-world guys would probably move so slowly that they also would never perceive the relativistic effects.

[Telepathic Intruder]

"Is there any stationary matter?"

It depends on reference frame. From your reference frame, you are stationary. Even if you're driving your car, from your reference frame you are stationary while the street is moving. The equivalence principal says that there are no absolute reference frames, only local ones. Relativity theory says that for every reference frame, time and space are different, which leads to time (and space) dilation at near the speed of light. That's from the point of an observer who's local reference frame is stationary, not the object going near the speed of light. That object's local reference frame is also a stationary one.

[Gadsden1st]

What color is a single photon? Are all photons the same color?

How does a single photon create the red shift if the speed of photons is constant regardless of the direction the source is moving?

[litehaus]

“Time does not exist for massless particles”

In that case, the word ‘particles’ describes what, if not matter ?

[P.O.E.]

Why does everything spin? Galaxies, electrons, etc.

[Telepathic Intruder]

"In that case, the word ‘particles’ describes what, if not matter ?"

Matter and energy are both particle/waves, but fermions (matter) have mass while bosons (energy) do not. What separates them is that matter is subject to the Pauli exclusion principal while energy is not. And the root cause of this is supposedly the Higgs field. This is basic quantum physics, not that any of it is simple or easy to grasp. Feynman once said "If you think you understand quantum mechanics, you don't understand quantum mechanics".

[dhs12345]

Photon is a particle. It makes more sense if you treat it as a wave (TEM) and Maxwells equations?

It has been a while for me though.

[litehaus]

“Matter and energy are both particle/waves, but fermions (matter) have mass while bosons (energy) do not. “

The older I get, the less I know/understand.....Is that like saying - Ice, Steam and Water are all just H2O,or something ?

What sets of what constitute each of those things?

[Telepathic Intruder]

"True wisdom is knowing what you don't know"--Confucius. The older I get, the more I know how little I know.

"Ice, Steam and Water"

You're talking about different phase states of water, which are solid, liquid, and gas, depending on temperature and air pressure. Einstein's E=mc² shows that matter and energy are really the same thing, but in different states, similar to phase states of water. You can change one to the other, and each has their own set of particles and wave functions.

The total set of elementary particles is not that complicated:



Fermions are leptons and quarks, which make up all matter. The bosons make up all energy. Atoms are not elementary particles, but compound ones, so you have more combinations of those.

This is sort of a hobby of mine, by the way. I have no official expertise.

[litehaus]

“Fermions are leptons and quarks, which make up all matter. The bosons make up all energy. Atoms are not elementary particles, but compound ones, so you have more combinations of those.”
What constitutes an elementary particle then? Are there many kinds? Are they something we engage while we live, or a picture of something that exists for ‘less than a moment’ on a ‘photo’ in/from some ‘tron machine/collider’ ?

[Telepathic Intruder]

Nope. They’re the limit of our knowledge.