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John Huth | USLHC | United States

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Turtles all the way down?

I recently got an interesting e-mail about the Big Bang. The writer said she didn’t see how you could make something out of nothing. She collects creation myths and thought that, no matter how you sliced it, it’s always “turtles all the way down.” This is a reference to creation myths where the world is poised on top of a turtle, which is itself poised on top of something else, but raises the issue: Is there any firm ground?

This is worth addressing because it illustrates the gulf between the understandings in people’s minds about the Big Bang on one hand, and how physicists deal with it on the other. To be clear – we have a wealth of observations that support the Big Bang, but you have to be careful. We can only look back into the universe to a moment 300,000 years after the ‘start,’ as best we can discern it. At this early moment, the universe went from being opaque to transparent. Before this moment, ionized gas kept light from traveling any distance, but once protons and electrons cooled enough to form neutral hydrogen, light (photons) could travel long distances. The remnant photons from this time are seen as the so-called cosmic microwave radiation. These photons were first observed by Arno Penzias and Robert Wilson in the 1960’s and continues to be a rich source of information about the early universe.

What do we see? We see galaxies moving away from each other. The further away we look, the faster they appear to recede. Einstein’s gravity has a number of solutions for possible universe structures. One of these solutions describes the expanding universe very well, and, if taken at face value, would extrapolate back in time to an initial state when all matter in the universe existed as a single point of infinite density. But, does a point of infinite density make sense? The author of the e-mail question thinks not, that it’s like pulling a rabbit out of the hat. You can’t make something from nothing, and this apparent absurdity invalidates the Big Bang model.

The main issue is that, although our observations are very consistent with this model of a Big Bang universe, we cannot actually see the initial moment. It’s hidden from view. We strongly suspect that the laws of physics might change dramatically when distances scales and energy densities approach the conditions very close to initial moment. We know that when the classical laws of physics are combined with quantum mechanics, new phenomena emerge. This was the case of our theory of electromagnetism. When we incorporated quantum mechanics with electromagnetism, the phenomenon of anti-matter became apparent. We have yet to find a satisfactory theory of gravity that combines quantum mechanics. The manifestations of quantum mechanics in gravity will only emerge at extremely high energy densities, such as those in the very early universe, near the time of this infinite density, and will likely modify our current models. For all we know, space-time might resemble some Escher print, eluding the concept of an infinite density starting point through a twisted configuration that folds in on itself.

Rather than dealing with a concept that seems almost theological in nature, physicists try to reconcile models against data. We fully realize that our models will extrapolate to conditions that raise difficult issues, like infinite densities. More often than not, the difficult conditions are something we avoid talking about, because, largely, we cannot really test or measure these. If it is inaccessible, it is inaccessible. The work can be perhaps more likened to the work of explorers. Our job is to map new territories, and, if anything, we can only report on territories we’ve explored. What lies beyond the horizon is a matter of speculation.
Responses? Questions? Contact me on Twitter @JohnHuth1

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15 Responses to “Turtles all the way down?”

  1. Gavin Flower says:

    Possibly the Universe is a multi-dimensional analogue of a sphere. So asking about what happened before the Big Bang, might be rather similar to asking what is south of the South pole!

  2. Jurjen says:

    Another way of putting is is that the moment before the big bang is “out of scope”.
    Physicists don’t know why there was a big bang, but that is also not what they are investigating.
    The big bang is a great way to describe the universe, and it is by far the simplest explanation for the observations. Therefore, it is a useful theory.

    • Gavin Flower says:

      According to some theories, the Big Bang was some sort of phase change where the number of dimensions changed and allowed matter & photons to begin to exist. I know there are other theories that postulate a Universe prior to the Big Bang, but I don’t recall any useful details. Some physicists are looking at patterns in the background radiation left over from the Big Bang, to see if there are artefacts that provide evidence to support some of those theories.

      However, I suspect most physicists simply avoid that problem as being too intractable!

  3. Emanuel Hoogeveen says:

    I would argue that the quantum fluctuations during cosmic inflation thought to cause the structure we see in the CMB did create ‘something’ from ‘nothing’ – that is, they created diversity: without them the universe would have stayed completely homogeneous. Of course the energy they acted upon had to be there in the first place – but it’s the fundamentally random nature of the universe that allowed its nature to change from a homogeneous point of undefined size to a place where fluctuations in density generate a concept of distance.

    If you believe in a completely deterministic universe, as some physicists still do, then it becomes a bit more difficult to explain the origin of said fluctuations – because they must have their origin in some specific configuration of that initial moment (which then implies multiple such configurations and the multiverse unless you can explain why that configuration is the only possible such configuration).

  4. EscapedWestOfTheBigMuddy says:

    In principle, of course, we could see further back (to the weak freeze out horizon) if we could image the cosmic neutrino background. In practice…

  5. joset says:

    Actually, we can extrapolate even further, into the Planck scale. And, if gravity bosons exist, that extrapolation can be enhanced even further. Beyond that scale though, conjectures abound…

    • John Huth says:

      Unfortunately we cannot extrapolate into the Planck scale. I wish that were the case. There is nothing that is currently accessible to experiment. As another commentator hinted, the existence of structure at some scales in the cosmic microwave radiation (CMB) might imply something about quantum fluctuations in the early universe, but this is an inference based on CMB.

      There are some interesting probes proposed based on polarization of CMB, which might give us a window into the inflationary epoch, which preceded the time when the universe became transparent. I’m eagerly awaiting the progression of the polarized CMB work, but this will only probe, at best, to the grand unified scale, which is still some orders of magnitude away from the Planck scale.

  6. Cormac says:

    What a succinct article. I have can think of several books that take many chapters to discuss the points made here.
    On succinctness, I sometimes wonder if we should portray the modern view of the singularity by changing the familiar refrain ‘asking about what happened before the Big Bang is similar to asking what is south of the South pole!’ to a more modern version: ‘asking about what happened at the Big Bang is like asking what direction one is facing at the South pole!’
    Regards, Cormac

  7. Jay Marx says:

    It may be possible to observe gravitational waves from the big bang which would give us a direct look at the universe something like 10**-21 seconds after the bang. This signal could be seen in the polarization of cosmic microwave background or, if some models are correct, directly with interferometric gravitational wave detectors such as Advanced LIGO. The more conservative models of inflation tells us that Advanced LIGO will still be orders of magnitude away from the required sensitivity. So maybe something for our grandkids.

    • John Huth says:

      Jay –

      Yes, you are correct. In one of my comments below I said that I was looking forward to results from polarized CMB. Now, this is interesting about Adv. LIGO – worth me digging into. Thanks for your comments!

      John

    • Chris Zizzo says:

      Your grandkids? Who are currently playing with advanced LEGOs?

  8. dequantizer says:

    The idea of single point with infinite density to be the primordial prerequisite of BGBG (big bang) is very challenging and enticing and bears tons of challenges to disprove it. More tantalizing is the conceptualization of space-time conversion from extremely high degree of opacity to virtual transparency that we are still experiencing until now.

    • John Huth says:

      I guess the thought I was trying to convey was that although the current cosmological solution implies a point of infinite density, it doesn’t guarantee that this is what really happened. As Jay Marx pointed out, there are probes that go beyond the transition to transparency, such as the polarization of CMB.

      Another point worth making, although this is more semantic – I would not say that space-time went from opacity to transparency, but, rather the ‘universe’ went from opacity to transparency. The distinction being that the latter is associated with the interactions of matter in the universe, as opposed to space itself.

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