How our Universe was born from nothing or whether there was anything that existed before it still remains a mystery, but that doesn't stop some physicists from trying to solve it.
As I understand it, nothing comes from nothing. For something to exist, a material or component must be available, and for that to be available, something else must be available. Where did the material that created the Big Bang come from, and what happened in the first instance to create that material in the first place? – Peter, 80, Australia.
"The last star will slowly cool and die out. With its departure, the Universe will once again sink into nothingness, without light, life, or meaning."
So warned physicist Brian Cox in a recent BBC series. Universe.
The extinction of the last star will be just the beginning of an infinitely long, dark epoch.
All matter will eventually be swallowed by monstrous black holes, which will themselves evaporate in dim flashes of light.
The universe will expand outward until even that faint light is too stretched out to interact.
All activities will cease.
Or will it?
To make things even more unusual, some cosmologists believe that a previous, cold, dark, empty universe like the one that awaits us in our distant future could have been the source of our own Big Bang.
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First matter
But before we get to that, let's take a look at how "material" - the first physical matter - came into being.
If we want to explain the origin of stable matter made up of atoms or molecules, such a thing certainly did not exist at the time of the Big Bang, nor for hundreds of thousands of years after.
We actually have a fairly detailed understanding of how the first atoms formed from simpler particles, once the environment cooled enough for more complex matter to become stable, and how these atoms later combined with heavier elements inside stars.
But this understanding does not explain the question of whether something came from nothing.
And so let's go back a little further.
The first long-lived particles of matter of any kind were protons and neutrons, which together make up the atomic nucleus.
They were created about one ten-thousandth of a second after the Big Bang.
Before that point, there was actually no material in the sense we know of.
But physics allows us to continue tracing the timeline backwards – all the way to the physical processes that precede any stable matter.
This brings us to the so-called "great united epochs".
We are now well into the world of speculative physics, because we cannot produce enough energy in our experiments to investigate the kind of processes that were taking place at that time.
But a plausible hypothesis is that the physical world was made up of a soup of short-lived elementary particles, including quarks, the building blocks of protons and neutrons.
There was both matter and "antimatter" in approximately the same amounts.
Each type of matter particle, such as a quark, has its own antimatter counterpart, a "mirror image" companion that is almost identical to it, but differs in only one aspect.
However, matter and antimatter annihilate in a flash of energy whenever they meet, meaning that these particles are constantly being created and destroyed.
But how did these particles come into being in the first place?
Quantum field theory tells us that even a vacuum, which supposedly corresponds to empty space-time, is full of physical activity in the form of energy fluctuations.
These fluctuations can cause particles to start popping up, only to disappear shortly afterwards.
This might sound like a mathematical quirk rather than real physics, but such particles have been observed in countless experiments.
The vacuum state of space-time teems with particles that are constantly appearing and disappearing, seemingly "out of nothing."
But perhaps all this tells us that the quantum vacuum (despite its name) is more something than nothing.
Philosopher David Albert is sharply criticized evidence of the Big Bang that promises that something came from nothing.
What if we asked ourselves: where did space-time itself come from?
Then we would have to turn the clock back even further, all the way to the truly ancient "Planck epoch" – a period so early in the history of the Universe that our best theories of physics fall flat.
This era occurred in the ten millionth billionth billionth billionth of a second after the Big Bang.
At this point, both space and time themselves have become subject to quantum fluctuations.
Physicists usually work separately with quantum mechanics, which governs the microworld of particles, and general relativity, which applies on large, cosmic scales.
But to truly understand each other Planck epoch, we need to complete the theory of quantum gravity by combining these two.
We still don't have a perfect theory of quantum gravity, but there are attempts at it - such as string theory and quantum gravity loop.
In these attempts, ordinary space and time are mostly experienced as something that is coming, like waves on the surface of a deep ocean.
What we experience as space and time is the product of quantum processes operating at a deeper, microscopic level – processes that don't make much sense to us creatures rooted in the macroscopic world.
In the Planck era, our usual understanding of space and time breaks down, so that we can no longer rely on our usual understanding of cause and effect.
Despite this, all potential theories of quantum gravity describe something physical happening in the Planck epoch – some quantum precursor to ordinary space and time?
But where did it come from?
Even if causality no longer holds in the most ordinary sense, one could still explain one component of the Planck-era universe in terms of another.
Unfortunately, at this point, even our best physical theories fail to fully provide us with answers.
Until we make further progress towards a "theory of everything," we will not be able to provide any definitive answer.
The most we can say with certainty at this stage is that physics has so far failed to find confirmed cases of something coming from nothing.
A cycle from almost nothing
To truly answer the question of how something could come from nothing, we would have to explain the quantum state of the entire Universe at the beginning of the Planck epoch.
All attempts to do so remain highly speculative.
Some of them invoke supernatural forces such as a creator.
But other candidates for explanation remain within the realm of physics – such as the multiverse, which contains an infinite number of parallel universes, or cyclical models of the Universe, which are born and reborn again and again.
Physicist awarded the 2020 Nobel Prize Roger Penrose proposed an intriguing but controversial model for a cyclical universe called "conformal cyclical cosmology".
Penrose was inspired by an interesting mathematical connection between the very hot, dense, small state of the Universe – as it was at the time of the Big Bang – and the extremely cold, empty, expanded state of the Universe – as it will be in the distant future.
His radical theory to explain this correspondence is that these new states become mathematically identical when pushed to their ultimate limits.
Although it may seem paradoxical, the complete absence of matter could have led to the creation of all the matter we see around us in the Universe.
According to this view, the Big Bang came about almost out of nothing.
It's what's left when all the matter in the universe is swallowed up in black holes, which in turn decay into photons – also lost to nothingness.
The entire universe therefore arises from something that is – seen from another physical perspective – as close to nothing as is possible.
But that nothing is somehow still something.
It is still a physical universe, however empty it may be.
How can the same state be a cold, empty universe from one perspective and a hot, dense universe from another?
The answer lies in a complex mathematical procedure called "conformal surveying," a geometric transformation that essentially changes the size of an object but leaves its shape unchanged.
Penrose showed how a cold, dense state and a hot, dense state could be related by such a measurement so that they matched in terms of the shape of their spacetimes – though not their sizes.
It is obviously difficult to understand how two objects can be identical in this way when they are two different sizes – but Penrose argues that size as a concept ceases to make sense in such extreme physical environments.
In conformal cyclic cosmology, the direction of explanation moves from old and cold to young and hot: the hot, dense state exists because of the cold, empty state.
But this "because" is not exactly familiar to us - in the sense of a cause followed in time by an effect.
And it's not just size that ceases to be relevant in these extreme conditions: the same happens with time.
The cold, dense state and the hot, dense state are actually located in different time planes.
The cold, empty state will continue forever from the perspective of the observer in his own temporal geometry, but the hot, dense state it enables practically inhabits a new, own temporal plane.
It might help to understand the hot, dense state arising from the cold, empty state if it were viewed in some non-causal way.
Perhaps we should say that the hot, dense state arises from, or is grounded in, or realized from the cold, empty state.
These are explicitly metaphysical ideas that have been studied extensively philosophers of science, especially in in the context of quantum gravity, in which it seems as if ordinary cause and effect no longer apply.
At the frontier of our knowledge, it becomes difficult to disentangle physics from philosophy.
Experimental evidence?
Conformal cyclic cosmology offers some detailed, albeit speculative, answers to the questions of where our Big Bang came from.
But even if Penrose's vision is confirmed by future advances in cosmology, we would think that we still have not answered a deeper philosophical question - the question of where physical reality itself came from.
How did the entire cycle system come about?
And then we are finally left with the pure question of why there is something and not nothing – one of the greatest questions of metaphysics.
But our emphasis here is on explanations that remain within the realm of physics.
There are three broad options for answering the deeper question of how the cycles began.
He may not even have a physical explanation.
Or there could be endlessly repeating cycles, each universe on its own, with the initial quantum state of each universe explained by some property of the universe before it.
Or there could be a single cycle, and a single universe, that repeats itself over and over again, with the beginning of that cycle explained by some property of its own end.
These last two approaches avoid the need for any unprovoked events – and this gives them a distinct appeal.
Nothing would remain unexplained by physics.
Penrose imagines a sequence of endless new cycles for reasons partly related to his own preferred interpretation of quantum theory.
In quantum mechanics, a physical system exists in a superposition of many different states simultaneously, and it just "chooses" one at random when we measure it.
For Penrose, each cycle involves random quantum events that turn out differently – meaning that each cycle will be different from those that came before and after it.
This is actually good news for experimental physicists, because it could allow us to peer into the ancient universe from which ours emerged through its faint traces, or anomalies, in the remnants of radiation from the Big Bang seen by the Planck satellite.
Penrose and his collaborators believe they may have already spotted these clues, attributing patterns in the Planck data. radiation from supermassive black holes from the previous universe.
However, the observations they claim to have had disputed by other physicists and there is still no final verdict on who is right.
Endless new cycles are key to Penrose's own vision.
But there is a natural way to convert conformal cyclic cosmology from a multi-cycle form to a single cycle.
Then physical reality exists in a single cycle from the Big Bang to a maximally empty state in the distant future – and then again in the exact same Big Bang, from which the exact same universe emerges.
This latter possibility is consistent with another interpretation of quantum mechanics, called the many-worlds interpretation.
The many-worlds interpretation tells us that every time we measure a system that is superposed, that measurement does not select a random state.
Instead, the measurement result we see is just one possibility – one that manifests itself in our own Universe.
The other measurement results all manifest in other universes in the multiverse, practically cut off from ours.
So, no matter how small the chance of something happening, if those chances are not zero, then it's happening in some quantum parallel world.
There are people just like you out there in other worlds, who won the lottery or got swallowed by the cloud of some weird typhoon or spontaneously combusted or did all three at once.
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Some people believe that such parallel universes are possible. to notice in cosmological data, as fingerprints made by another universe colliding with ours.
Quantum many-worlds theory puts a new spin on conformal cyclic cosmology, though not one that Penrose agrees with.
Our Big Bang could be the rebirth of a single quantum multiverse, containing countless other universes all happening simultaneously.
Anything possible happens – and then it happens again, and again, and again.
Ancient myth
For a philosopher of science, Penrose's vision is fascinating.
It opens up new possibilities for explaining the Big Bang, taking our explanations beyond mere cause and effect.
Therefore, it is a great test case for exploring the different ways that physics can explain our world.
He deserves more attention from our philosophers.
For a mythology lover, Penrose's vision is beautiful.
In Penrose's preferred multi-cyclic form, it promises an infinite number of new worlds born from the ashes of their ancestors.
In one form of a single cycle, it is a strikingly contemporary evocation of the ancient idea of the ouroboros, or world-serpent.
In Norse mythology, the serpent Jormungandr is the child of Loki, the clever trickster, and the giantess Angrboda.
Jormungandr swallows his own tail and the resulting circle maintains the balance of the world.
But the myth of the ouroboros is documented all over the world – even in ancient Egypt.
The ouroboros of a cyclical universe is truly magnificent.
In its belly it contains our own Universe, as well as every one of the strange and wonderful alternative possible universes made possible by quantum physics – and at the point where its head meets its tail, it is completely empty, yet energy flows through it at temperatures of hundreds of thousands of millions of billions of trillions of degrees Celsius.
Even Loki, of elusive form, would be impressed.
Alistair Wilson is Professor of Philosophy at the University of Birmingham.
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