READER QUESTION:My understanding is that nothing comes from nothing.
Peter, 80, Australia.
The last star will slowly cool and fade away.
With its passing, the universe will become once more a void, without light or life or meaning.
So warned the physicist Brian Cox in the recent BBC seriesUniverse.
The fading of that last star will only be the beginning of an infinitely long, dark epoch.
Space will expand ever outwards until even that dim light becomes too spread out to interact.
But that understanding doesnt address the question of whether something came from nothing.
It’s free, every week, in your inbox.
So lets think further back.
These came into existence around one ten-thousandth of a second after the Big Bang.
Before that point, there was really no material in any familiar sense of the word.
But physics lets us keep on tracing the timeline backward to physical processes which predate any stable matter.
This takes us to the so-called grand unified epoch.
But how did these particles come to exist in the first place?
These fluctuations can give rise to particles popping out, only to disappear shortly after.
The spacetime vacuum state is seething with particles constantly being created and destroyed, apparently out of nothing.
Simulation of quantum vacuum fluctuations in quantum chromodynamics.
Wikimedia/Ahmed Neutron
Suppose we ask: where did spacetime itself arise from?
At this point, space and time themselves became subject to quantum fluctuations.
We still dont have a perfect theory of quantum gravity, but there are attempts likestring theoryandloop quantum gravity.
But where didthatcome from?
Unfortunately, by now even our best physics fails completely to provide answers.
All attempts to do this remain highly speculative.
Some of them appeal to supernatural forces likea designer.
The 2020 Nobel Prize-winning physicistRoger Penrosehas proposed one intriguing but controversialmodel for a cyclical universedubbed conformal cyclic cosmology.
His radical theory to explain this correspondence is that those states become mathematically identical when taken to their limits.
In this view, the Big Bang arises from an almost nothing.
But that nothing is still a kind of something.
It is still a physical universe, however empty.
But this because is not the familiar one of a cause followed in time by its effect.
It is not only size that ceases to be relevant in these extreme states: time does too.
The cold dense state and the hot dense state are in effect located on different timelines.
At the limits of our knowledge, physics and philosophy become hard to disentangle.
Experimental evidence?
But our focus here is on explanations which remain within the realm of physics.
There are three broad options to the deeper question of how the cycles began.
It could have no physical explanation at all.
The latter two approaches avoid the need for any uncaused events and this gives them a distinctive appeal.
Nothing would be left unexplained by physics.
Ongoing cycles of distinct universes in conformal cyclic cosmology.
However, their claimed observations have beenchallenged by other physicistsand the jury remains out.
Map of the cosmic microwave background radiation.
ESA and the Planck Collaboration
Endless new cycles are key to Penroses own vision.
But there is a natural way to convert conformal cyclic cosmology from a multi-cycle to a one-cycle form.
This latter possibility is consistent with another interpretation of quantum mechanics, dubbed the many-worlds interpretation.
Many-worlds quantum theory gives a new twist on conformal cyclic cosmology, though not one that Penrose agrees with.
Everything possible happens then it happens again and again and again.
An ancient myth
For a philosopher of science, Penroses vision is fascinating.
It opens up new possibilities for explaining the Big Bang, taking our explanations beyond ordinary cause and effect.
It is therefore a great test case for exploring the different ways physics can explain our world.
It deserves more attention from philosophers.
For a lover of myth, Penroses vision is beautiful.
In Penroses preferred multi-cycle form, it promises endless new worlds born from the ashes of their ancestors.
Jormungandr consumes its own tail, and the circle created sustains the balance of the world.
But the ouroboros myth has been documented all over the world including as far back as ancient Egypt.
Ouroboros on the tomb of Tutankhamun.
Djehouty/Wikimedia
The ouroboros of the one cyclic universe is majestic indeed.
Even Loki, the shapeshifter, would be impressed.
