Bursting balloons – a fresh look at the Big Bang

We’ve just been watching the BBC’s enjoyable Horizon programme “Is everything we know about the Universe wrong?“.

Clearly a title designed to grab viewers. I confess a dislike to this kind of wording because it implies that we might all be wasting our time, and that we’ll one day have to throw away all our textbooks. The homeopaths out there say “ha!” and start prescribing leeches again. But this is a mistake. When Einstein corrected Newton on gravity, it did not overturn 300 years of teaching. If our model of the universe, known as the Standard Model, can be improved by a newer model, all physicists would welcome it. And since we know the Standard Model doesn’t cover everything, we hope this will happen. The program showed scientists discussing “unwelcome” wrinkles in new evidence, which doesn’t fit the model. These are never “unwelcome” – scientists love to see well-derived new evidence, because it invariably leads us to new models and new ideas. A well-known physicist once told me over a beer that the most boring thing that could come out of the LHC is the Higgs Boson. What they really want, is a whole new world of unexplained phenomena.

My main gripe with the show, but really with the presentation of cosmology in general, is in the repeated assertion and explanation of the Big Bang as an explosion. The BBC used two common effects repeatedly. The fireball explosion (82 times) and the inflating balloon (86 times).

Let me state this clearly. The Big Bang was not an explosion, or at least, not as we see one: from a single point, expanding spherically outwards into empty space. This model is both inaccurate and misleading. We know that this is not true due to measurements of cosmic drift, the Hubble Effect. Everything is moving away from everything else. This is explained in my textbook with a balloon! The idea is that points drawn on the surface of a balloon get further from each other as the balloon expands. I contend that this is a misleading explanation because your average student will not be able to get his mind away from the fact that this is a balloon, inflated from a central point – and will therefore miss any explanation of the surface detail.

My preferred explanation of cosmic expansion is to use the grid of shifting measurement detailed in a previous musing. I shall expound further on this notion here, and describe how I imagine the expansion of the universe, in my mind. If you haven’t read that post before, please do so, to clarify any doubts you may have of an infinite universe that is able to expand without a central point.

I shall start in the present. At the current time, the Universe contains an even distribution of galaxies, which can be broadly seen to be without start nor end nor centre.

Some time ago, we believe matter in the universe to have been closer together. In your mind, for this mental experiment, I would like you to imagine that instead of matter being closer together, I would like you to imagine that matter was larger. For the sake of argument, twice as large. And I mean, on every level, from the computer your read this on, down to the atomic level and below.

Between that time and now, let’s say matter has simply collapsed together, become more compact, with more space around it. There is no need for a driving “dark energy” to inhabit the darkest regions between the galaxies; it is the galaxies themselves that draw together. This effect is greatly outweighed by gravity, so the stars and galaxies we see can still stay together.

I’d like you to imagine back further, to the time immediately after the Big Bang. Picture for me the Universe to the scale we see it today, but that protons and neutrons are enormous – the size of planets. Electrons are like footballs bouncing around the gaps. And there are loads of them – no vast gaps of space that we see between planets. There is the same number of atoms in the universe then and now. So everything is so close together, what with being so large, that collisions are commonplace, and that everything gets very hot.

Again, fast-forward to today. Everything has shrunk together, remaining attached by the forces we’re familiar with, the electromagnetic holding atoms together and gravitational holding gas clouds together. As spaces grew between particles, the particles were pulled one way or another, clumping to form stars, planets, galaxies, black holes.

How would we see this today? As a gradual separation of galaxies, the Hubble Effect, which might appear to accelerate slightly, as the groups of matter become more dense. We’d see strange effects near the edges of galaxies, where the collapse at the core was filtering out to the edges. You might see flat rotation curves.

And how could we back up a concept of collapse rather than expansion? What could explain this? I’d like to turn to every cosmologist’s adversary, quantum theory. With the scales of particles so large in the early universe, it’s easy to see that the probability waves of quantum theory could play a major role. Even today, we don’t know at what scale the quantum systems break down. We’re as close to knowing whether Schrödinger’s cat could be a real quantum system as when it was first proposed. Perhaps systems could be larger in the early universe. Perhaps it is not that the particles were larger, but that their wave function was larger.

Mass can be considered a concentrated point of energy. The conversion of tiny quantities of mass into energy is what fuels nuclear reactors and atomic bombs. And we know mass distorts spacetime, an effect we see as gravity. Could this distortion be fuelling cosmic collapse?

But regardless of any scientific justification, I find the mental model of matter collapse far more appealing than cosmic expansion. There are no balloons or explosions (regrets to the BBC effects/repeats dept), with their implicit ideas of central expansion, so it’s a lot easier to understand.

Does it make sense to you too?

  • I think the balloon ranks up there with the mattress and two different size balls, to explain gravity.

  • kennethkufluk

    I think the elastic sheet and the balls can be really good for gravity. It's just shifting that into 3D that's difficult. The balloon is different, because you're immediately mislead by a completely wrong notion – that of a “centre of the universe”.

    Looking again at the elastic sheet, I can see that a heavy mass created a dent. And so my mind is thinking, “where is it pulling?” At the edges of the sheet, the elastic is pulled taut, but this doesn't factor into the gravitational dip. What is the analogy of this in spacetime?

  • Actually, my other half “Get's it” using the whole bed thing, but like you say, it's hard for her to image it in full 3D.