When did time begin?
Everyone is familiar with the concept of time but when did it begin? Graihagh Jackson put this cosmic quandry to Cambridge philosopher Huw Price and Imperial cosmologist Roberto Trotta...
Huw - Many cosmologists now think that there is. This view goes back to a discovery that the universe is expanding, a discovery made in the 1920s. Logical implication of that is that there must have been a time when it was at minimum size and that's what we now think of as the Big Bang. On most views, that's the beginning of time. There's literally nothing before that.
Graihagh - Basically, with the Big Bang, time was created. Time didn't exist before the Big Bang because well, the Big Bang created time. Armed with the best physics in the 20th century, Albert Einstein came to a very similar conclusion with his theory of relativity which states that time isn't quite the same everywhere. Planet Earth's hefty mass warps time. It's why the clocks on orbiting satellites run slightly slower and why astronauts on the International Space Station returned having aged slightly less, although not by much it must be said. That's an aside, but the big picture here is that space and time is warped by mass and because all the mass in the universe would've been contained in something smaller than an atom, it would've brought time to a standstill. Ergo, the beginning of time is the Big Bang or is it?
Huw - Well, there are cosmologists who think that the Big Bang wasn't really the beginning. What happened was that instead of collapsing like that, the matter bounced and so, people talked the Big Bounce rather than the Big Bang. It's a cycle of bounces and collapses.
Graihagh - So then that means time is infinite and there is no beginning of time if it's continually contracting and expanding though.
Huw - Yeah, exactly.
Graihagh - The message I'm taking away is, either you believe in the Big Bang and that before the singularity, there was no such thing as time. At that massive expansion, that is when time was created or you believe in the Big Bounce and that means time was infinite and there is no beginning of time.
Huw - Yeah, I think those are the two basic options. But of course one of the nice things about science in general and physics in particular is that it has a delightful way of coming up with new options so we can't be absolutely sure that something else won't come along.
Graihagh - Time was infinite then or it begins with a Big Bang, simple. But where do cosmologists sit? Is there any evidence that supports either theory? Roberto Trotta from Imperial College London gave me the lowdown of first was the Big Bounce.
Roberto - This picture is actually in doubt today because we now know that our universe is not going to recollapse. It is actually going to expand forever.
Graihagh - Sorry how do we know that our universe isn't going to recollapse?
Roberto - And that's because of dark energy. 70 per cent of our universe is made of an unknown type of force or energy that we call dark energy, whose main impact on the universe is to make the expansion of the universe accelerate with time. So, not only the universe is growing with time today. It's growing at an ever accelerating speed and it will not be a big crunch that will end our universe. The end will be a state of darkness where all the matter will have been sucked into black holes.
Graihagh - A slightly scary space. That sounds something of a sci-fi movie.
Roberto - Yes, but it's about 200 billion years in the future so there is nothing to worry about.
Graihagh - So, that theory is in doubt. What other theories might there be that have more support?
Roberto - Some ideas are rather different. They postulate the existence of parallel universes effectively so. Our universe is made of a 3-space dimensions and 1 time dimension. So, it's a 4-dimensional universe. But what if there were additional dimensions that we cannot actually penetrate ourselves?
Graihagh - Five dimensional spaces and universes being sucked into black holes. This all sounds a little mindboggling to me but fortunately, Roberto had some lasagne to hand to show me how parallel universes could work.
Roberto - Okay, let's give our parallel universes 4 minutes.
Graihagh - So whilst this quickly heating up, this is to demonstrate the various parallel universes, so you've got layers of vegetable because this is a vegetarian lasagne because this is a vegetarian lasagne I noticed. And then you've got the layers of pasta and cheese. So, what signifies what here?
Roberto - The layers of pasta are going to symbolise and represent the different parallel universes separated by something which in this case is the vegetable filling. You'll have other layers which are just universes just like us, but they are separate from us across the 5th dimension and that's the dimension where the stuffing resides.
So now, we're going to cut the lasagne in the middle to reveal nicely our parallel universes. Yes, we can see there are about 4 or 5 parallel universes in it. Now, the idea is that if we have gravity leaking through the two lasagne layers, the two pasta layers would be smashed together. They will be attracted one to the other and when they hit like this, they're going to splash all the sauce out and this is going to be the Big Bang effectively.
Graihagh - If this theory is correct, it means not only are there an infinite number of universes but also, time too is infinite. But that's a big 'if'. Will we ever know for sure?
Roberto - It's very difficult to say. I think it's actually quite impressive to be able to say that we can now reconstruct with a high degree of fidelity the history of the universe from today, 13.7 billion years after the Big Bang to the very beginning some 10-32 seconds after the Big Bang. All that remains to be tested is this tiniest sliver of time 10-32 seconds after the Big Bang. And so, in a sense, the job of scientists at the forefront of research is always that of pushing back the limit of the unknown. And so now, we are really hitting the very hard, very deep, very fundamental questions.
Graihagh - What existed before the Big Bang? Well, it's still an open question. Perhaps nothing, perhaps another universe or perhaps a different version of our own, perhaps even a sea of universes. This is one problem that won't stay dead. In the decades following Einstein's death, the advent of quantum physics has resurrected questions about the pre-Big Bang universe. And no doubt, with many more additional discoveries to be made in the next century, our ideas may well be very different in the decades to come.