The last star will fade away. The Universe will become a void with its passing.
Cox warned in the series Universe. The fading of that last star will be the beginning of a long, dark period. All matter will eventually be eaten by black holes, which will evaporate away into the dimmest light.
The space will expand until the light is too dim to interact. The activity will stop.
Will it? The source of our Big bang could be found in a previous, cold dark empty Universe like the one we are in today.
The first thing.
Let's take a look at how "material" came about. There was no explanation of the origins of stable matter made of atoms or molecules after the Big bang.
We have a pretty detailed understanding of how the first atoms formed out of simpler particles, and how they were later fused into heavier elements inside stars. The question of whether something came from nothing is not addressed by that understanding.
Let's think back further. The first long-lived matter particles were protons and neutrons. Around ten thousandth of a second after the Big bang, these came into existence.
There was no material before that point. We can keep on tracing the timelines backwards to the physical processes that preceded the stable matter.
This leads us to the grand unified epoch. We are well into speculative physics as we can't produce enough energy in our experiments to probe the sort of processes that were going on at the time.
A plausible hypothesis is that the physical world was made up of a soup of short-lived particles.
There was both matter and antimatter in the same quantities and each type of matter particle had a mirror image companion.
Matter and antimatter are destroyed in a flash of energy when they meet.
How did these particles come to be? According to quantum field theory, a vacuum is full of physical activity in the form of energy fluctuations. The fluctuations can 888-269-5556 888-269-5556 888-269-5556s can 888-269-5556 888-269-5556 888-269-5556s can 888-269-5556 888-269-5556 888-269-5556 888-269-5556s can 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556s can 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556 888-269-5556
This may sound like a mathematical quirk, but such particles have been spotted in many experiments.
The spacetime vacuum state is seething with particles being created and destroyed. The quantum vacuum is a something, not a nothing, so perhaps all this tells us.
David Albert has criticized accounts of the Big bang which promise to get something from nothing.
Where did spacetime come from? The clock can be turned further back, into the "Planck epoch", a time when our best theories of physics break down.
This era was only one tenth of a trillionth of a trillionth of a second after the Big bang. Space and time became subject to fluctuations.
Physicists work with quantum mechanics and general relativity separately, which apply to large, Cosmic scales. We need a theory of quantum gravity to fully understand the Planck epoch.
We don't have a perfect theory of quantum gravity, but there are attempts. Ordinary space and time can be seen as waves on the surface of a deep ocean in these attempts.
The quantum processes that make up space and time don't make sense to us as creatures in the macroscopic world.
Our ordinary understanding of space and time is broken down in the Planck epoch, so we can't rely on it anymore.
All candidate theories of quantum gravity describe something physical that was happening in the Planck epoch, which is a quantum precursor of ordinary space and time. Where did that come from?
It is possible to explain one component of the universe in terms of another, even if causality no longer applies. Our best physics fails to provide answers. We won't be able to give a definitive answer until we make further progress towards a "theory of everything".
The most we can say with confidence is that physics has so far found no evidence of something.
The cycles were from almost nothing.
We need to explain the quantum state of the entire Universe at the beginning of the Planck epoch in order to answer the question of how something could arise from nothing.
Attempts to do this are very speculative. They appeal to supernatural forces. There are other explanations within the realm of physics, such as a multiverse, which contains an infinite number of parallel universes, or a model of the Universe being born and reborn again.
Roger Penrose, winner of the 2020 Nobel Prize in physics, has proposed a model for the universe that is controversial.
Penrose was inspired by a mathematical connection between a very hot, dense, small state of the Universe and an extremely cold, empty, expanded state of the Universe, as it will be in the future.
His theory is that when states are taken to their limits, they become identical. It might seem odd, but a total absence of matter might have given rise to all the matter we see around us.
The Big Bang is seen from almost nothing. When all the matter in a universe has been consumed into black holes, which have in turn boiled away into photons, that's what's left over.
The whole universe arises from something that is as close to nothing as one can get. Nothing is still a kind of thing. It's still a physical universe.
How can a cold, empty universe from one perspective and a hot, dense universe from another be the same? Conformal rescaling is a mathematical procedure that alters the size of an object but leaves it's shape the same.
The hot dense state and the cold dense state could be related by rescaling so that they match the shapes of their space times.
It's difficult to understand how two objects can be the same in this way when they have different sizes, but Penrose argues that size doesn't make sense in such extreme physical environments.
The direction of explanation goes from old and cold to young and hot because of the cold empty state. This is not the usual cause followed in time by its effect. Size and time are not relevant in these extreme states.
The hot dense state and the cold dense state are in effect on different timelines. The cold empty state would continue forever from the perspective of an observer in its own temporal geometry, but the hot dense state would effectively occupy a new timeline all its own.
It may help to understand the hot dense state that is produced from the cold empty state. Maybe we should say that the hot dense state comes from the cold, empty state.
Philosophers of science have explored these ideas extensively in the context of quantum gravity, where ordinary cause and effect seem to break down. It is difficult to disentangle physics and philosophy at the limits of knowledge.
Experimental evidence?
The question of where the Big bang came from is speculative, but formal cyclic cosmology offers some detailed, albeit speculative, answers. If Penrose's vision is vindicated, we might think that we wouldn't have answered a deeper question about where physical reality came from.
How did the system of cycles come about? One of the biggest questions of metaphysics is why there is something rather than nothing.
Our focus is on explanations that are within the realm of physics. The deeper question of how the cycles began is one of the three broad options.
It could not have a physical explanation. The initial quantum state of each universe could be explained by features of the universe before. There could be one cycle and one repeating universe, with the beginning of that cycle explained by a feature of its own end.
The two approaches that avoid uncaused events give them a distinctive appeal. Nothing would be left unexplained.
A sequence of endless new cycles is what Penrose has in mind. In quantum mechanics, a physical system is in a superposition of many different states at the same time, and only one is picked randomly when we measure it.
Each cycle involves random quantum events turning out a different way, meaning that each cycle will be different than the last. This is good news for physicists because it could allow them to see the old universe that gave rise to ours through faint traces, or anomalies, in the leftover radiation from the Big bang.
Penrose and his team believe they may have spotted these traces already, by using the data from the previous universe. The jury is out because their claimed observations have been challenged by other physicists.
Penrose's own vision is dependent on new cycles. There is a way to convert a multi-cycle to a one-cycle form. Then physical reality consists in a single cycle through the Big Bang to a maximally empty state in the future, and then again to the very same Big Bang, giving rise to the very same universe all over again.
The many-worlds interpretation of quantum mechanics is consistent with this latter possibility. The many-worlds interpretation tells us that the measurement doesn't randomly select a state when we measure a system that is in superposition. The measurement result we see is just one of many possibilities.
Our own measurement results are cut off from the other universes in a multiverse. If it has a non-zero chance, then it will happen in a quantum parallel world.
There are people out there who have won the lottery, been swept up into the clouds by a freak typhoon, or have done all three at the same time.
Some people think that parallel universes may be observable in the data of our universe.
Penrose doesn't agree with the new twist on conformal cyclic cosmology given by Many-worlds quantum theory. Our Big bang might be the rebirth of a single quantum multiverse, containing many different universes. Everything can happen, then it happens again and again.
An old myth.
Penrose's vision is interesting for a philosopher of science. It opens up new possibilities for explaining the Big bang. It's a great test case for exploring the different ways physics can explain our world. It needs more attention from philosophers.
Penrose's vision is beautiful for a lover of myth. Penrose's preferred multi-cycle form promises endless new worlds from the ashes of their ancestors. It is a modern re-invocation of the ancient idea of the ouroboros, or world-serpent.
The giant Angrboda is a clever trickster and the child of the serpent Jrmungandr. The balance of the world is maintained by the circle created by Jrmungandr. The myth of ouroboros has been documented all over the world.
The ouroboros of the one universe are majestic. It contains within its belly our own Universe, as well as every one of the weird and wonderful alternative universes allowed by quantum physics, and at the point where its head meets its tail, it is completely empty, but also has energy at temperatures of a hundred thousand million billion trillion degrees Celsius
The shapeshifter would be impressed.
Professor of Philosophy at the University of Birmingham.
The Conversation's article is a Creative Commons licensed one. The original article can be found here.
