Could there be a universe larger than ours, such that ours is a subatomic particle by its standards? And is it possible that, within the particles we know of, there are smaller universes?
Nick Canning
Coleraine, County Londonderry, UK
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You seem to have an image of multiple universes stacked within each other like Russian dolls, but with the possibility of the number of such dolls being infinite. This isn’t how our universe works.
Our observable universe, a sphere of radius about 46.5 billion light years (enlarged from the expected 13.9 billion light years due to the continual expansion during the time since the big bang) is, under the current standard cosmological model, part of an infinite, flat universe. So, our observable universe is then only a minute fraction of the universe.
But to call it a subatomic particle is misleading. That suggests the laws of physics applicable would be those of subatomic particles and that is definitely not the case. The universe on these scales is essentially dominated by classical mechanical behaviour.
In such a big universe, subatomic particles would be completely deterministic little balls bouncing around
Are the actual subatomic particles, which are governed by the laws of quantum mechanics, themselves harbouring smaller universes? No, not of a form similar to our observable large-scale universe.
The geometry of the universe is not that of a fractal, which would be self-similar at all scales. There is an absolute scale delimiting large from small set by Planck’s constant, h. The wave-particle nature of bodies is captured by de Broglie’s relation: wavelength = h ÷ momentum. This sets the scale at which wave mechanics becomes more important than classical particle mechanics in the physical description of nature and separates the small from the large.
Danny Kermode
Vernon, British Columbia, Canada
No. At very small scales, quantum mechanics rules. The uncertainty principle says that we can’t know both the speed and position of a particle with complete accuracy. At a human scale, we can’t directly observe this phenomenon, but it defines the mechanics of subatomic particles. At scales smaller than that, individual objects and causal mechanics wouldn’t exist.
That rules out a tiny universe. What about a universe where our universe occupies the space of just one particle? Life requires chemistry, and there can be no chemistry without quantum mechanics. In such a large universe, subatomic particles would be completely deterministic little balls bouncing around. There could be no life.
So the answer is obviously no. Or is it? Quantum theory isn’t truth, it is a theory. In science, the only truths are direct empirical observations. The mathematics that we associate with observations and the predictions that we make from the mathematics are abstracted from those observations. We can never be 100 per cent certain that the next observation won’t prove our analyses to be false.
We can attempt to apply our theories to universes on a scale that we can’t directly observe, but we cannot claim that anything we say about them is “true” or “false”. Quantum theory provides compelling evidence that the tiny and huge universes can’t exist, but it doesn’t say that they are impossible. That which isn’t impossible is, from a purely semantic point of view, possible.
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