Skip to comments.Cosmic uncertainty: Is the speed of light really constant?
Posted on 03/10/2017 3:40:14 PM PST by 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.
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.
(Excerpt) Read more at newscientist.com ...
Gravity may have chased light in the early universe
By Michael Brooks
Its supposed to be the most fundamental constant in physics, but the speed of light may not always have been the same. This twist on a controversial idea could overturn our standard cosmological wisdom.
In 1998, Joao Magueijo at Imperial College London, proposed that the speed of light might vary, to solve what cosmologists call the horizon problem. This says that the universe reached a uniform temperature long before heat-carrying photons, which travel at the speed of light, had time to reach all corners of the universe.
The standard way to explain this conundrum is an idea called inflation, which suggests that the universe went through a short period of rapid expansion early on so the temperature evented out when the cosmos was smaller, then it suddenly grew. But we dont know why inflation started, or stopped. So Magueijo has been looking for alternatives.
Now, in a paper to be published 28 November in Physical Review, he and Niayesh Afshordi at the Perimeter Institute in Canada have laid out a new version of the idea and this one is testable. They suggest that in the early universe, light and gravity propagated at different speeds.
If photons moved faster than gravity just after the big bang, that would have let them get far enough for the universe to reach an equilibrium temperature much more quickly, the team say.
A testable theory
What really excites Magueijo about the idea is that it makes a specific prediction about the cosmic microwave background (CMB). This radiation, which fills the universe, was created shortly after the big bang and contains a fossilised imprint of the conditions of the universe.
In Magueijo and Afshordis model, certain details about the CMB reflect the way the speed of light and the speed of gravity vary as the temperature of the universe changes. They found that there was an abrupt change at a certain point, when the ratio of the speeds of light and gravity rapidly went to infinity.
This fixes a value called the spectral index, which describes the initial density ripples in the universe, at 0.96478 a value that can be checked against future measurements. The latest figure, reported by the CMB-mapping Planck satellite in 2015, place the spectral index at about 0.968, which is tantalisingly close.
If more data reveals a mismatch, the theory can be discarded. That would be great I wont have to think about these theories again, Magueijo says. This whole class of theories in which the speed of light varies with respect to the speed of gravity will be ruled out.
But no measurement will rule out inflation entirely, because it doesnt make specific predictions. There is a huge space of possible inflationary theories, which makes testing the basic idea very difficult, says Peter Coles at Cardiff University, UK. Its like nailing jelly to the wall.
That makes it all the more important to explore alternatives like varying light speeds, he adds.
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“Gravity may have chased light in the early universe”
If there were no Matter, would there be Time ?
Better unanswerable question, Huh ?
Our galaxy is 100,000 light years across, and it is more than four years light traveling time even to Proxima Centauri, the closest star to the sun and home, possibly to a habitable planet rather like Earth.But that is not what the linked article says about Proxima B.
The planet is rocky, of a similar mass to Earth, and temperate all conditions that are promising for life. But Proxima B isnt a second Earth. The similarities end there, says [Guillem] Anglada-Escudé. Even our knowledge of the surface temperature is fairly uncertain, ranging from a possible 33°C to the high hundreds, depending on its atmosphere.Quite a bit of leeway in the speculation.
Thats just the average temperature. However, Proxima B and its star are probably tidally locked, so the same face of the planet always points towards the star. So one half of the globe is in perpetual day, the other in never-ending night. Thats not very Earth-like, Anglada-Escudé says.
Oh goody speculative physics from guys with grants
Ok, I am not sure light is a constant. But its used as a constant because its far and a way from other things. But what if different light has different speeds. There is more than one type of light. And it seems that each has a unique speed but all of them are realistically far from everything else but not exactly the same. Like two stars are millions of light years apart but sufficiently far as to be relatively similar when used in any formula.
Great post. Interstellar Ping!
I have long been an ‘undocumented’ theoretical physicist. I am fascinated by stuff like this, and I thank you for posting...
I recently read about this new theory, that the speed of light was much greater in the past and is slower now. All speculation until proven somehow.
What puzzles me is how light photons can travel billions of light years without fizzling out. We can see galaxies in the form they were billions of years ago, if their light has taken that long to reach us. How can light keep going in space for billions of years, with a small amount of energy within each photon? A combination of wave, particle,... and magic?
Light goes slower if its not in a vacuum. But I think the variance that physicists are wondering about is something else. If as the universe expands the speed of light and a vacuum has changed....but I have not even read the article yet because I am at work and need to do work stuff....just dropping a ping comment....
Well, the speed of light varies depending on the medium, or the vacuum, that it passes through. Let’s make a wormhole to send signals FTL
Withdraw their freebie grants and they would be lucky to get employed at McDonald’s.
Not if it’’s trying to shine through the rinos and demo to get to the deep state.
Quite the question huh?
Does global warming slow down the speed of light? What’s the consensus? /sarc
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