Drawing the line

There has been some noise out there in the matrix about a recent book by Lawrence Krauss called "A Universe from Nothing".


It has been seized upon by by the atheist community (and to lay my cards on the table, I am an atheist) as another nail in the coffin for the God Delusion.

It has gone so far that Richard Dawkins (husband of the wonderful Lalla Ward, one of the Doctor's greatest companions) has said in the forward
"This could potentially be the most important scientific book with implications for supernaturalism since Darwin."
and
“Even the last remaining trump card of the theologian, ‘Why is there something rather than nothing?,’ shrivels up before your eyes as you read these pages. If ‘On the Origin of Species’ was biology’s deadliest blow to super­naturalism, we may come to see ‘A Universe From Nothing’ as the equivalent from cosmology. The title means exactly what it says. And what it says is ­devastating.”
I haven't read the book (but will once I have gotten Violent London and Dr Euler out of the way), but, sorry, this madness has to stop. We need to draw a firm line in the sand on what is science, and what is not (and as I hope to show, a distinct line isn't even possible!).

Where to start. I think the starting place is a rather robust discussion I had with colleagues when I was recently in France. Some may have called it an argument, others might suggest that I was vigorously lecturing the others in the room, but robust it was. The point of discussion, in summary, was the dodgyness of modern cosmology.

The discussion ranged far and wide, and I was attempting to defend cosmology. The problem was that word cosmology was used to encompass many things, from the redshift of galaxies, the temperature of the CMB and baryon wiggles, through dark matter, dark energy and quintessence, and into mutiverses, brane cosmologies and freaky cosmologies.

The problem was that using a single word, cosmology, to encompass all of these things, was then used to paint the entire topic with a single brush, suggesting that because papers on multiverses are often daffy in the extreme, and that there is no physical evidence for colliding branes, that the entire topic should be dismissed as pseudoscience and thrown in the bin.

I feel my blood pressure rising again, so here is a calming picture.

Like a lot of things, cosmology is not a single "thing" but a whole collection of observations, theoretical models, guesswork, and darn-right fairy tales.

There are some things we are pretty certain of. Galaxies out there are redshifted, and that redshift increases with distance. I have measured this myself for a handful of galaxies, and I know people who have collectively measured the redshifts for millions of galaxies. Either there is something completely screwed with the laws of physics, or we are pretty certain of this. I would bet my house that galaxies are redshifted - it's an observation thing.

Now comes the tricky bit. Why are they redshifted. Well, the only physical theory we really have that lets us calculate properties of the universe at large is general relativity (and this, this exceptionally vital point, is often lost in the media haze surrounding cosmology), and that actually predicts what we see. Galaxies should be moving away from us. But only if the universe "expands", such that the distance between objects get larger with time.  I am a big fan of relativity and so I would put my car on this interpretation of what we see being correct.

But there is a problem. To get the rate of expansion with distance that we see, we need a lot more matter than we can actually observe (i.e. all the stars and gas out there), and so we need a dark matter component. Worse than that, we need to add an even more mysterious dark energy component to get the universe to accelerate.    

Sometimes in the media, dark matter and dark energy sound like something a bunch of tipsy cosmologists dreamt up of in the pub just to annoy everyone else. But they are not. In relativity they are precisely defined in terms of their large scale properties. If you don't have them in the equations, then it just doesn't work.

Yes, general relativity may be wrong, and so we could be being fooled, but I'm willing to bet a few hundred dollars this is not the case, that general relativity is a pretty good description of the expansion of the universe, and so we need a dark sector to account for what we see.

While general relativity tells you about the bulk properties of the dark sector, it does not (and, more importantly, cannot) tell you what dark matter and dark energy actually are. This starts to mean that bets are off and speculation begins.

As long as it is dark, and behaves like matter, it is a dark matter candidate.

As long as it is dark, and causes the universe to accelerate (like a cosmological constant), it is a dark energy candidate.

For any particular candidate, I might be willing to bet a dollar here or there, but really, I am not convinced of a lot of ideas. Actually, quite a lot of them belong in science fiction.

And then we hit the biggy. If we run the universe backwards it has a time zero, a big bang where the distance between any pair of points is zero. The birth of the universe.          

BOOOOOMMMM!!!!!

But where did it come from? Surely this is where science meets religion? If science can show that the universe arose in a purely physical process, then that puts an end to the "God did it" excuse?

Yes, it does, but we cannot answer that question. And to understand why is easy. Here's the history of the universe.
where closer to today is at the bottom. As we work our way upwards, the two key aspects of physics are at work, with general relativity controlling the expansion of the universe, while quantum mechanics does all of the cooking of particles, atoms and molecules. And it works wonderfully, until that annoying time at the top. The Planck Time!

There is a lot of fluff written about quantities with the word Planck in front of them, but (as yet) they are really a sign where something has gone wrong. We know that at and before the Planck time our knowledge of the laws of physics fails. At this earliest epoch of the universe, both quantum mechanics and general relativity influence all of the processing going on, and we need them to work together, and what we know is that they simply don't (I'll write more on this at another time).

When we reach this point, there is no way we can use the laws of physics to wind back the clock and ask what happened before. If there was *only* general relativity, we know that the distance between objects goes to zero and we have the Big Bang, but with quantum mechanics in the mix, all bets are off and, and I'll put this in bold, until we have a mathematical theory of gravity and the other forces that work together in the immense temperatures and density of the early universe, we simply cannot see before this point.

Here is a picture I made a number of years ago to illustrate this (this is, in fact, an updated version by the very smart, and Bayesian-master, Brendon Brewer)



The solid black line is the "general relativity only" cosmology, the purple is the Planck time (not to scale) and the green is what really might have happened to the universe. Basically, just about anything.

And so we reach the question of "what happened before the Big Bang?". Honestly, we don't know and we reach the realm of speculative cosmology. Brane collisions, vacuum fluctuations, self-reproducing universes, the myriad ideas that are out there. But again, while they may have mathematics behind them, they are still little more than speculation. The best they can do, in terms of observational evidence, is match the standard cosmological models in terms of predictions.

This is important. There is not a shred of evidence to distinguish all of the multitude of speculative "before the Big Bang" models from the standard general relativistic picture. We know that our laws of physics break down in the early universe, but, who knows, the general relativity picture may be correct and the universe was really born out of nothing, a real nothing. Until we get our physics to work back through the Planck time, we just don't know.

This brings us back to Krauss's book (and again, I have not read it, but will and comment). While there are a number ideas presented in there for pre-Big Bang universes, as of yet, they may all be completely and utterly wrong and what really happened may be something completely different.

There is nothing wrong with presenting such ideas, as they may be the starting point for really understanding the universe. But I think it is essential for us to be honest that what we have now are nothing really than a collection of ideas, speculations and, in some cases, fairy tales, and to suggest that we have really started to address the question of what happened before the Big Bang, is somewhat dishonest. The question is more open than evolution, even in the time of Darwin.

I realize I have written a lot here, so I'm going to take a breather, and take Mini-Me #1 to rugby. More soon.

Comments

  1. I've worked up quite a head of steam myself about this.

    http://letterstonature.wordpress.com/2011/04/01/of-nothing/
    http://letterstonature.wordpress.com/2011/04/16/more-sweet-nothings/

    I think it's even worse than you make out.

    1. While a beginning is not certain, it has proven rather stubborn. Inhomogeneities won't prevent a singularity, neither will the pressure of matter create a bounce (Hawking Penrose). Inflation doesn't seem to help (Borde, Guth Vilenkin). Even if you could make a bounce, the universe might not get there due to instabilities. There are still singularities in perturbative string theory. So if quantum gravity is going to swoop in and save the day then it’s got some work to do. The evidence on this side of the Planck divide all points the same way. (www.newscientist.com/article/mg21328474.400-why-physicists-cant-avoid-a-creation-event.html) Vilenkin concludes. "All the evidence we have says that the universe had a beginning."

    2. Science cannot answer the question "why does anything at all exist?". Science postulates some properties of the universe, deduces what we would observe and then tries to see if we guessed right. At no point do we do anything that could tell us why there is anything to describe with our equations.

    ReplyDelete
  2. Geraint, this is a great post. Good to see the old classic temp.jpg wheeled out once again, too.

    Quite frankly it annoys me when people on "my side" in the religion wars use terrible arguments such as this. You don't have to know where the universe came from to be an atheist. If it did have a beginning, then three possible explanations might be (1) God (theist type) (2) god (deist type) or (3) something else that we don't understand.

    I'd assign my probabilities as {0.001, 0.099, 0.9}. And the practical implications of (2) are closer to (3) than they are to (1).

    ReplyDelete
    Replies
    1. Hi Brendon, do you really assign probability of 10% to a deist-type creator? I'll take a bet with at 10:1 odds :-)

      Geraint, nice post, I agree that Dawkins has gone over the top in his enthusiasm for his mate's book.

      Tim

      Delete
    2. Hi Tim, I'd be happy to take your bet, but I don't know how we're ever going to find out. :-)

      Delete
    3. I would pay out if a message is found encoded in the digits of pi (as in Carl Sagan's "Contact") :-)

      Delete
    4. I'm sure that if you go deep enough into pi, you can find the complete works of Shakespeare.

      Delete
  3. > So if quantum gravity is going to swoop in and save the day then it’s got some work to do.

    I agree - but with a glass-half-full hat on, my personal weighting is that it will save the day. But that is nothing but my personal preference :)

    As for temp.jpg - I really should make a new version!!

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  4. At least cosmologists now actually seem to be talking about what happened before the Big Bang. That was taboo a few years ago.

    I admire your urge for caution. Whilst I love all the theories, they are very perplexing to us laymen and - in the end - only one of them might be proved right. It reminds me of the 'Big Bang' v 'Steady State' debate, which now seems so long ago.

    As for religion, it contains a lot of astonishing (and contradictory) theories too. The difference being that we already know for certain that none of their ridiculous hypotheses stack up, whilst the various competing cosmology theories will almost certainly drop off, one by one, until the right theory is left standing.

    ReplyDelete
  5. From Greybeard (for some reason his comments aren't appearing)


    At least cosmologists now actually seem to be talking about what happened before the Big Bang. That was taboo a few years ago.

    I admire your urge for caution. Whilst I love all the theories, they are very perplexing to us laymen and - in the end - only one of them might be proved right. It reminds me of the 'Big Bang' v 'Steady State' debate, which now seems so long ago.

    As for religion, it contains a lot of astonishing (and contradictory) theories too. The difference being that we already know for certain that none of their ridiculous hypotheses stack up, whilst the various competing cosmology theories will almost certainly drop off, one by one, until the right theory is left standing.

    ReplyDelete
    Replies
    1. Unfortunately -

      "whilst the various competing cosmology theories will almost certainly drop off, one by one, until the right theory is left standing."

      is not guaranteed, and we may be left with no theories left standing....

      Delete

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