Answer by Philip Mott
Q. There’s been much recent media hype surrounding the alleged discovery of ‘proof’ for the Big Bang theory – but what has actually been found and what does it mean?
A. Well we don’t really know whether anything has been found yet. The BICEP2 team claim to have found a pattern in the polarisation of the Cosmic Microwave Background Radiation (CMBR) – however this has yet to be confirmed by separate observations, so the whole thing may yet turn out to be a red herring.
Q. Ok, but suppose this pattern is confirmed – what, if anything, would it prove?
A. All it would really prove is that there’s a polarisation pattern in the CMBR.
Q. Really? Why are they going on about the Big Bang then? Actually, before you answer that, what’s the CMBR?
A. It’s the name we give to the thermal radiation in the microwave region of the electromagnetic (EM) spectrum that we observe here on Earth coming from all directions in the universe.
Q. Aren’t microwaves just like light waves, only at a wavelength our eyes can’t see?
Q. So if our eyes could see these microwaves, the sky would appear all lit up at night-time?
A. That’s right.
Q. What on earth could cause that?
A. Nobody knows for sure, since nobody was there to see what caused it.
Q. But isn’t it associated with the Big Bang somehow?
A. By some, yes – according to the Big Bang theory, the CMBR was created around 380,000 years after the Big Bang when the universe had cooled down enough for the protons and electrons to combine into atoms, causing the universe to become transparent to EM radiation. But that’s only one explanation – for an alternative one, see here.
Q. So if the CMBR was caused by some other phenomenon, then this polarisation pattern could have nothing to do with a Big Bang?
A. That’s right.
Q. Why are they getting so excited about this polarisation pattern anyway?
A. Because they think it’s evidence for cosmic inflation.
Q. What’s that?
A. It’s a theory that tries to account for various observational evidences that contradict the Big Bang theory by claiming that the universe went through a brief period of extremely rapid exponential expansion in the first fraction of a second after the Big Bang.
Q. What could have caused that?
A. They’re not sure – their current theories are purely hypothetical.
Q. Is there any direct observational evidence for it?
A. No, and there never could be.
Q. So how do they know it happened?
A. They don’t, but the alternative is that the Big Bang theory is wrong.
Q. What are these contradictory evidences anyway?
A. Well according to the Big Bang theory, the temperature of the CMBR should be significantly different in different directions, but it isn’t (known as the Horizon Problem). When combined with Grand Unified Theories, it also predicts that there should be magnetic monopoles all over the universe – in fact they should be its primary constituent – but we haven’t even found one (known as the Monopole Problem). Finally, the average density of matter and energy in the universe seems uncannily close to the critical density required for a flat universe (known as the Flatness Problem).
Q. I think I’ve heard of that last one before – can you unpack it a little for me?
A. According to the Big Bang theory, the average density of the universe determines its space-time curvature, which can be spherical, flat or hyperbolic. They typically use a quantity they refer to as Ω to measure this. If Ω is less than 1 the universe is hyperbolic, if Ω is greater than 1 it’s spherical, and if Ω is exactly 1 then it’s flat. Given that in a random universe Ω could have any positive value, it seems very strange that it should have such a specific one.
Q. But I think I’ve read somewhere that it would have to be close to 1, or stars and galaxies and thus life itself wouldn’t have been possible and we wouldn’t be here to talk about it.
A. Yes that’s known as the Anthropic Principle, but Big Bang theorists still see it as a major problem because of just how close it is to 1.
Q. How close are we talking?
A. Immediately after the Big Bang, within 10-62
Q. That’s unbelievably small!
A. And that’s only limited by the accuracy of our current equipment – it could be even closer.
Q. So there are these major problems with the Big Bang theory, but rather than conclude that the theory is wrong, they’ve come up with this inflation theory to try to explain away the problems?
A. Yes, and as I’ve mentioned, inflation is very unsatisfactory – it’s even criticised by secular theorists.
Q. But if this is their attitude regarding contradictory evidence, how would it ever be possible to falsify the Big Bang theory?
A. Good question. And I’m afraid it’s quite common – they do the same with Dark Matter and Dark Energy, which are similarly only hypothesised due to contradictory evidence.
Q. But isn’t there a great danger that such an approach would lead to these theories becoming more of a worldview than anything to do with the truth?
A. I’d say that’s more than a danger, it’s already happened.
Q. Ok, so you say there’s no direct observational evidence for inflation, but what about this polarisation pattern?
A. They claim it was caused by gravitational waves which were in turn caused by inflation.
Q. But there’s no way of knowing whether that was actually the case?
Q. What else could it have been caused by?
A. I asked the physicist on that weblink I mentioned earlier about this since he specialises in this area, and he told me that the same polarisation was found a year ago, but not at the angular scale they were looking for, so they attributed it to gravitational lensing by massive objects since this can produce the same effect. So that remains a possibility. He said that another alternative is the action of plasma filaments in the CMBR, which can cause a similar lensing of light, and could have produced a similar polarisation effect due to Birkeland currents within the filaments. Even according to the Big Bang theory the gravitational waves could have been caused by phase-change effects other than inflation.
Q. So, like you said at the beginning, assuming the observations are confirmed, all they would really prove is that there’s a polarisation pattern in the CMBR?
For more information on this topic see the Question: Big Bang Inflation is claimed to have been discovered. What do you think? Answer here.
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