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https://www.newscientist.com/article/2113797-gravity-may-have-chased-light-in-the-early-universe/
Gravity may have chased light in the early universe
By Michael Brooks
It’s 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 don’t 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 Afshordi’s 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 won’t 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 doesn’t 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. “It’s 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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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 isn’t 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.
That’s 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. “That’s 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.
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?
Awesome
Not if it’’s trying to shine through the rinos and demo to get to the deep state.
Does global warming slow down the speed of light? What’s the consensus? /sarc
A rumor travels faster then light.
The speed of light is constant, even in matter. The ‘speed of light’ in a transparent material is just the net perceived macroscopic interference wavefront from a vast number of individual absorptions, excitations, and emissions of the constituent atoms in the material. Light travels the vacuum from atom to atom at c. Also, “the speed of light” is a much deeper concept, and is a structural constant of spacetime, and exists independent of the particular properties of photons. In a universe without electromagnetic radiation, c would still exist, but would not be quite so convenient to measure.
You can prove the speed of light is not constant with nothing more than a sunbeam and a glass of water.
On March 4, the moon occulted the star Aldebaran (Alpha Tauri). Initial reports indicate that Aldebaran was not harmed. But light from Aldebaran which had been racing towards the earth for 65 years hit the moon a little more than a second before it would have reached its goal. What a disappointment for those rays of light—almost at their goal and splat! they hit the moon instead.
The Decreasing Speed of Light - Dr. Barry Setterfield
https://www.youtube.com/watch?v=QdTlOVTDbNU
Are not gravity waves believed to “bend light”. If so, can/do they also effect the speed of light?
In the very tiniest early fraction of the beginning of the “big bang”, isn’t it said that it was all energy and none of it had “cooled” into any form of matter, and if true was there then no gravity yet to speak of. And that’s true then could light have been - for some period of “time” - very much faster than it is today?
Or I am too ignorant and just asking a question learned physics would say is dumb.
A photon travels at at the speed of light. A photon is a particle. What holds the particle together? A photon is made of yet smaller particles. What holds each of those smaller particles? Whatevertheyare that glue must move faster than light. We just don’t know about them yet.
Just when we thought the atom was the basic particle, we find dozens of smaller particles.
I think that light speeds up the closer you are to an intersection when the light turns yellow.
Light is affected by gravity, ie objects in space. So, not constant.