Cosmic Horizons

Over on youtube,  Veritasium  has a nice discussion of  Misconceptions about the Universe.  I  like it, especially as I was the consultant cosmologist :) A little look down the comments tho, and we see several claims that what Derek says is not correct. Here's a little excerpt Well, as a cosmologist, I was surprised to read that the  Hubble Sphere  is an "outdated concept" having seen it used in a professional meeting last week. But let's take a look at the other claims that are made by "fullyawakened" - I must admit they have the lead on me as I am partiallyjetlagged at the moment. As ever, I am going to steal  Tamara Davis's  standard cosmological picture in a few different sets of coordinates to do this. I've explained these before, but the top one has distance as we know it along the x-axis, and time as we experience it up the y-axis. "Our observable Universe is getting smaller" is simply wrong. Let's look at the bottom fi

Sorry, I've been traveling. I'll be posting soon, but please check out a recent article of mine over at the Conversation called  Have Cosmologists Lost their Minds in the Multiverse?

Back from an exhausting week in Canberra allocating grants for the Australian Research Council.  Handing out a few tens of millions of dollars really takes it our of you. The sad part is not the excellent projects we funded, but the many excellent projects we could not as we ran out of cash. Anyway, the meetings are confidential, so I can't discuss them here. But time to catch up on some of my own science. There is something super exciting coming, so here I'll focus on a merely excellent piece of work by globular cluster finder extraordinaire,   Avon Huxor  (excuse his ever so happy face!). I've written many times about the  Pan-Andromeda Archaeological Survey , our superb survey of our nearest neighbour, the  Andromeda Galaxy.  As well as identifying lots of substructure, the shredded remains of small galaxies, we also see lots of globular clusters, balls of roughly a million stars living together. The Milky Way has about a hundred of these orbiting in the halo. Andro

Your mind can wander into some strange areas when lying in bed in the early hours of the morning, in the quiet before the kookaburras start laughing their heads off. When we read about dark matter, it often easy to think that it's out there, far away from Earth, like black holes, neutron stars, and little green men. But it's important to remember that the orbit of the Sun around the Galaxy depends upon not only the stars we see, but the dark matter we don't. In fact, we have to remember that dark matter surrounds and threads our Solar System. But just how much? Anyone who has done any university physics knows that within the Solar System we can happily use Newton's laws of  gravitation  and  laws of motion  to calculate the paths of the planets, with the Sun as the massively dominant source of gravitational pull, with the planets just providing additional little tugs. If there is dark matter in the Solar System, it seems to be irrelevant. Just how much dark ma