Cosmic Horizons

Proton: a life story  by Geraint F. Lewis 10 35 years: I’ve lived a long and eventful life, but I know that death is almost upon me. Around me, my kind are slowly melting into the darkness that is now the universe, and my time will eventually come. I’ve lived a long and eventful life… 10 -43 seconds: A time of unbelievable light, unbelievable heat! I don’t remember the time before I was born, but I was there, disembodied, ethereal, part of the swirling, roaring fires of the universe coming in to being. But the universe cooled. From the featureless inferno, its character crystalized into a seething sea of particles and forces. Electrons and quarks tore about, smashing and crashing into photons and neutrinos. The universe continued to cool. 1 second: The intensity of the heat steadily died away, and I was born. In truth, there was no precise moment of my birth, but as the universe cooled my innards, free quarks, bound together, and I was suddenly there!...

Obligatory "sorry it's been a long time since I posted" comment. Life, grants, student, etc All of the usual excuses! But I plan (i.e. hope) to do more writing here in the future. But what's the reason for today's post? Namely this video posted on your tube. The conclusion is that humans are destined to explore the Local Group of galaxies, and that is it. And this video has received a bit of circulation on the inter-webs, promoted by a few sciency people. The problem, however, is that it is wrong. The basic idea is that accelerating expansion due to the presence of  dark energy  means that the separation of objects will get faster and fast, and so it will be a little like chasing after a bus; the distance between the two of you will continue to get bigger and bigger. This part is correct, and in the very distant universe, there will be extremely isolated bunches of galaxies whose own gravitational pull overcomes the cosmic expansion. But the rest, just ho...

With the recent  BICEP2  results, the question of the  Multiverse  has raised it's less than pretty head. The Multiverse is a topic which polarizes people, some who embrace the idea that our Universe is just one of countless trillions and trillions and trillions of other universes out there. Others get a little cross with the popularity of the topic. And then there are those (looking at you slashdot commenters) who generally talk nonsense. Over at  Starts with a Bang  Ethan Siegal tells us that  The Multiverse is not the answer.  The essential crux of Ethan's argument is that, in calling on the Multiverse, cosmologists are giving up on science. What does he mean? The Multiverse is not a single concept, there is more than one kind, but the basic idea is that, as well as our Universe, which we find quite cosy for life, there are a myriad of other universes. These universes are not identical to our own, but possess different physics, differe...

I'm not going to join the chatter on the  BICEP2 result  as there's already a lot of commentary out there (although  ABC News 24  seem to have missed it, so no chance to mess it up :) So, a tiny post today. Here's a picture from the BBC story. This is supposed to be the Big Bang, with galaxies rushing from a  central explosion. I've written about this before, but this is not what the Big Bang was. It was not an explosion in preexisting space. If we take the cosmological parameters as we currently know then (and assume a simple  topology ) then the Universe is now infinite in extent. And it was a billion years ago, and it was 13.5 billion years ago, and it was throughout the history of the Universe. When the Universe was a 100 million billion degrees celsius, it was this temperature everywhere throughout the infinite Universe. As it cooled down, it cooled down everywhere in the infinite Universe. When it got to a few hundred thousand years afte...

I'm a big fan of  Derek Muller's  youtube channel  Veritasium . It discusses lots of cool scientific topics, and presents a deep understanding of the underlying physics in a fun and entertaining manner. His most recent video asks the question  "Will this go faster than light?" , looking at ways of failing to break the Universal Speed Limit. Right at the end, Derek discusses the speed of light in a cosmological context, and mentions that out in the expanding Universe, there are galaxies that are moving away from us faster than light, which he then goes onto say that we can't see because of their speed. Is this correct? Derek is in good company, as lots of renowned physicists have made similar comments; here's  Richard Feynman  (taken from  this great article  which I very much recommend if you are interested in this topic). But alas, even the great Feynman can be wrong. Want to see something moving faster than light? Here you go. This,...