Friday, September 03, 2010

God, Stephen Hawking and the BBC

The currently most-read article on the BBC website has this headline "Stephen Hawking: God did not create Universe". As a Christian who has studied a fair bit of physics, I'm going to discuss that. Quick summary of my conclusions: Hawking has got it a bit wrong, but the media are over-sensationalising it as usual. And in the process, they are providing a massive amount of free advertising for Hawking's new book.

It's worth pointing out that I haven't read Hawking's article, because it's behind the Times' paywall, or Hawking's book, because it hasn't been published yet. But at this stage of his career, Hawking is far more a populariser of ideas than an original thinker, so I've got a pretty good idea where he is coming from on this...

The BBC quotes Hawking as writing:

Because there is a law such as gravity, the universe can and will create itself from nothing.

Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist.

It is not necessary to invoke God to light the blue touch paper and set the universe going.

Science and Religion

It's worth explaining a few things from these quotes. Firstly, Hawking's philosophy of how God acts in the universe. Hawking seems to have a kind of "God of the gaps" idea going on here - he only sees it as "necessary to invoke God" when there is no other explanation for something.

Of course, Hawking isn't stupid enough to go down the classic God of the Gaps line. He'd probably draw a distinction between when it is "necessary to invoke God" - i.e. when there is no other explanation for something, and when it is possible to invoke God - i.e. when there is an explanation for something that includes the possibility that God is behind it. The Christian answer - that science describes the way that God chooses to run the world - would be treated as when it is possible to invoke God rather than when it is necessary to do so.

Hawking is still wrong though. Rowan Williams is better (quoted on the front of the Times Online today):

Belief in God is not about plugging a gap in explaining how one thing relates to another within the Universe. It is the belief that there is an intelligent, living agent on whose activity everything ultimately depends for its existence.

In other words, Rowan Williams (correctly IMO) asserts that God's existence and action is necessary for science to keep working at all. God and Science aren't competing explanations for the same phenomenon.

Of course, the journalists seem to have even less understanding of this, and think that because Hawking says it isn't necessary to invoke God, he's denying God was involved at all. That's partly because it sells more papers or gets more people looking at the website, and partly because they don't have sufficient understanding of the topic to report accurately on it.

Creation and Quantum Fluctuations

The other thing that is worth explaining is what it means for Hawking to write that "Because there is a law such as gravity, the universe can and will create itself from nothing."

In quantum physics, things do sometimes just appear out of nowhere, and then vanish again. But when they do, the total amount of energy involved multiplied by the time they last for has to be less than about 10^-34 Js. So an electron / positron pair, for example, could only last about 10^-21s - one thousand billion billionth of a second. And something bigger would last even less long. So we don't see them very often and they don't usually make much difference to the universe on a big scale.

But that is the only known way of getting something out of nothing. So if the universe wasn't created - it just happened - that's the only known way for it to happen. The problem with that of course is that the universe has lasted quite a while - roughly 14 billion years. Therefore, in order for this theory to work, it needs to have almost exactly zero total energy.

The only known way of having a sufficiently large amount of "negative energy" is through gravity. Imagine that there is a lump of rock a very long way from the Sun, and it isn't moving. Now imagine that it falls towards the Sun, and in doing so it speeds up. It has clearly gained kinetic energy because it is moving. At a year 7 level, we'd say it has converted Gravitational Potential Energy (GPE) to Kinetic Energy (KE). But at the start, its total energy was zero, and at the end its KE is positive, therefore its GPE must be negative.

It's often asserted in astrophysics circles that Black Holes have zero total energy, because all the negative GPE cancels out the positive energy from their mass. And therefore it is possible to get something out of nothing if the something is a black hole because it has zero total energy. On the other hand, I've done a masters course in astrophysics, and I've never once seen that calculation done, or even referenced. Personally, I don't believe it, and I believe it even less when it comes to saying the universe as a whole has zero total energy, but am happy to change my mind if given a good reference that doesn't just assert it.

If it was true, it should mean that you get black holes popping into existence and staying there quite often, and we don't see that happening.

But the idea here is that many cosmologists think that that is what happened with the universe - it popped into existence as a kind of unstable black hole with zero total energy that then exploded. And that's what Hawking means by saying that gravity allows the creation of something from nothing.

(Images from NASA)
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