Following is part of an article titled, "What is reality"
Origins Excerpt
Even though we don’t fully understand what reality is – and may never do so – that doesn’t stop us from asking where it came from. It will come as no surprise that answering this question is far from easy. Just ask the people whose day job it is. They don’t agree on much, except that it is a tough gig. “We are in a difficult situation,” says Daniele Oriti at the Max Planck Institute for Gravitational Physics in Germany. “We are fishes in the pond and trying to infer the situation of our pond.”
The conventional origin story of the pond is the big bang. In this account, the universe simply popped into existence out of nothingness 13.8 billion years ago, triggering an expansion that has continued without pause ever since. It is a picture that aligns well with the available evidence – such as the ongoing expansion of the universe – but hasn’t yet been definitively accepted.
Perhaps that is no surprise given the unfathomable core of the big bang theory: how nothingness can give rise to an entire universe. Another major stumbling block is the moment just after the universe popped into existence, when its entirety would have been concentrated into a point of infinite density and temperature. “We do not have any theory that describes the universe at ultra-high temperatures and ultra-high densities,” says Anna Ijjas, also at the Max Planck Institute for Gravitational Physics. That means our knowledge of these first few instants remains fundamentally incomplete.
Better theories might yet fill these gaps. Or they might render them obsolete by showing that there was no beginning for space and time. That is the explanation Ijjas favours. She says that our universe’s beginning coincided with a previous universe’s end. Think of it as an hourglass, with two halves connected by an incredibly narrow neck. In this model, the universe would once have had a radius of 10-25 centimetres, more than a billion times smaller than the radius of an electron. That is vanishingly small, but infinitely bigger than the nothingness required for the big bang.
This hourglass model is known as the big bounce, and it has dramatic consequences for reality. Because theoretical calculations dictate that the preceding universe must have been similar to our own, its origin must also be similar. That means it, too, would have begun from the collapse of a preceding universe, and so on throughout eternity. “In our model, space-time never vanishes,” says Ijjas. In other words, reality has always existed and there was no beginning.
That seems difficult to imagine. “It’s somewhat counter-intuitive,” concedes Ijjas. But the alternative – the total absence of reality before space and time came into existence – is more difficult. “It’s infinitely more difficult,” she says.
What came before?
Oriti favours another alternative. For him, the big bang represents not the birth of the universe, but the moment the universe assumed its current form, with intelligible properties such as space and time. He compares it to a phase transition such as the moment steam condenses to liquid water. “All sorts of notions that you apply as a fish in the water simply do not apply to a gas,” he says.
Before this phase transition, notions of space and time are meaningless, and reality itself becomes fundamentally indescribable. Even the word “before” is inaccurate, says Oriti. “The notion of time ceases to apply.” What’s more, because all phase transitions are, at least in theory, reversible, the universe could return to this timeless state again at some point in the future, presumably with dire consequences for us. If “future” is even the right word.
This inability to talk about reality in everyday terms seems incredibly frustrating. “We get frustrated as well,” says Oriti. “I sympathise, but get used to it.” Reality, it seems, is truly beyond words.
Is reality the same everywhere?
Jason Arunn Murugesu
TRAVEL anywhere in the known universe and, like Coca-Cola, the laws of nature always taste the same. That is a basic tenet of physics called the cosmological principle, which holds that our patch of the universe is a representative sample of the rest.
This, as far as we can tell, is true. Certainly in the bits of the universe that we can see, the laws of physics are “uncannily the same”, says Richard Bower at Durham University in the UK. But an important caveat here is “the bits we can see”. What about those we can’t?
There are bits of the universe that are out of sight. Forever. These aren’t the exotic parallel universes conjured up by string theory or quantum mechanics, but an unavoidable consequence of workaday cosmology. Because the universe is expanding at breakneck speed yet the speed of light is finite, the outer reaches of the universe have disappeared over the cosmic horizon, forever out of contact as light from them could never reach us. The known universe inside the horizon stretches about 46 billion light years in all directions. How much there is beyond that isn’t known, but it is possible that there are places beyond the horizon where the laws of physics are different.
One reason for thinking this may be true is that our laws are bizarrely and arbitrarily conducive to life. Cosmologists call this fine-tuning. If any of the laws of physics were slightly different, we couldn’t exist. As just one example, if the strong nuclear force, which holds protons and neutrons together inside atoms, were slightly stronger, the sun would have exploded long before life got started on Earth. There are many other examples of fine-tuning, collectively known as the “Goldilocks paradox” because so many of the laws are just right. And paradoxical it is. “There’s no explanation for why they are the value they are,” says Bower. “You’ve just got to go, ‘That’s the way it is’.”
The odds of a universe with the exact specifications that can sustain life are so low that many physicists argue that there must be other places where the laws are different. It just so happens that we live in a life-friendly patch of universe because, well, it couldn’t be any other way.
And that’s just in our universe. There are almost certainly others. Multiverses are a consequence of many theories, including black hole physics and string theory. Not all produce different laws of physics, but some do. String theory, for instance, conjures up 10500 universes, all with different laws of physics.
Could we ever know if any of this is true? The reality is that other universes, if they exist, are probably forever inaccessible to us. “Multiverse theories must in principle be taken quite seriously, but proposals to test them don’t get very far,” says Simon Friederich at the University of Groningen in the Netherlands.
For now, we have to study what we can see. But there is an upside to this: it makes reality tractable. “If there is just one universe, then we might have a good chance of discovering basically everything about physics,” says Tim Blackwell at Goldsmiths, University of London. Unfortunately, that would be like assuming you understood all of biodiversity by cataloguing life on a small island. Reality may well be different elsewhere, but the cosmos is too big for us to know for sure.
