I know I keep saying it, but time is squeezed so a brief post today. And that's on another paper that I had accepted yesterday (I am still trying to catch up on the Christmas list... Ah well, I will get to those eventually).
I've written before about the work I have done on "The Cosmic Horizon". It's a long story, but there have been claims that this is a magical part of the Universe which has not been properly understood and modern cosmology has it all wrong etc. Simply put, these claims are wrong, but they keep appearing.
So, this new paper was in response to another paper which claimed our previous paper was wrong. As ever, the claims are wrong, as I describe.
As I've stated before, horizons are important things in cosmology, and there are some classic papers which describe their importance. There is another important quantity in cosmology, called the Hubble Sphere. Objects on the Hubble Sphere are moving away from us at the speed of light; to the rival papers, the Hubble Sphere is the mysterious "Cosmic Horizon".
There has been huge confusion over the years about what you can see in the Universe, and how can you observe things moving faster than the speed of light etc. If you find yourself in this state, I suggest you read this.
To cut to the chase, the claim is that the Hubble Sphere is a horizon, and that the light rays we receive are limited by the presence of the horizon (i.e. they can only go through it in one direction etc). In this paper, I showed that it is simple to make the Hubble Sphere increase and decrease by just mucking about with the constituents of the Universe, changing the spots of dark energy.
A picture speaks a thousand words:
The red lines are light rays which, after the Big Bang, move away from us, then some turn around and arrive back as the observer. Notices that one light ray, the one that arrives at the observer at a time of 130 billion years after the Big Bang, crosses the blue line three times, in differing directions. This is not Horizon-like behaviour.
In fact, in mucking about with the make up of the Universe, I could make the blue line dance in and out, and play with a photon, making it cross the blue line as many times as I wanted before we observed it. Simply put, the blue line is well understood. It's the Hubble Sphere. It is not a magical Cosmic Horizon.
And just to make Prajwal smile, I did the calculations in Python.
Well done ... errrm .... me :)
Phantom Energy and the Cosmic Horizon: Rh is still not a horizon!
Geraint F. Lewis
(Submitted on 2 Jan 2013)
There has been a recent spate of papers on the Cosmic Horizon, an apparently fundamental, although unrecognised, property of the universe. The misunderstanding of this horizon, it is claimed, demonstrates that our determination of the cosmological makeup of the universe is incorrect, although several papers have pointed out key flaws in these arguments. Here, we identify additional flaws in the most recent claims of the properties of the Cosmic Horizon in the presence of phantom energy, simply demonstrating that it does not act as a horizon, and that its limiting of our view of the universe is a trivial statement.