Saturday, 14 March 2009

A trip to Intech: What can we know about the Universe? by Russell Stannard

At 6:30 p.m. on the second Wednesday of each month, Intech Planetarium hold a space lecture by a visiting speaker. I did the October one (the subject of which I'm sure you can't possibly guess), and last Wednesday I nipped back to watch one by a writer who subtly changed things for me at a very early age: Professor Russell Stannard.

Russell Stannard wrote the "Uncle Albert" series which I often recommend to people on the forum when they ask questions about time, space, relativity, black holes etc. I read them when I was about 9 or 10, a good age to be introduced to concepts that don't make intellectual sense - at that age your mind is like a springy sponge, ready to twist and absorb anything; whereas by your twenties it'll be more like a brick, inflexible and it's harder to soak things up (at least if you're out of practice; not if you aren't, that's for sure!). I believe it's due to these books that I drove my GCSE Physics class insane with irritation throughout every unit on waves, and, more importantly, have always been fascinated by physics and astronomy, had some grounding in their weirdness, and always able to accept relativity and quantum physics despite the brain's logical barrier to them. I'll write more about the books themselves another time. Suffice to say I've been grateful to Russell Stannard for more years than I have anyone else, and it seemed well worth spending two days on a train to go and hear what he had to say.

Another Zooite, John, also came to Intech and we had a look around the science centre. It's a nice interactive place where you can bounce cubes around on strings, knock things onto the floor, play with smoke, torches and pulleys, and see pictures of pairs of socks modelling chromosomes and of the SDSS telescope. My favourite bit that particular evening was messing around with what was to me a mysterious machine, but which John tells me is called a harmonograph. It works by having a pen attached to one pendulum, and a clipboard and paper attached to another swinging at right angles. To see how it's built, here's a site John sent!


I didn't manage to make anything spectacular, but I couldn't resist taking my two home with me, and pinching three others that someone else had left behind:


Eventually it was time to dig our tickets out of our pockets and head for the planetarium. It's arranged with seats amphitheatre style, and a beautiful domed roof, dotted with a few stars poking through the rainbow colours the six cameras cast along the ceiling. The Powerpoint bit looked straight, because they cleverly cut out a slightly curved (on a flat screen) black rectangle - and then project the powerpoint onto that.

Sitting and waiting while the guests filed in, I got butterflies in my stomach all over again remembering my own first ever public lecture in this very room. We had a roof of galaxies over our heads: the Hubble Ultra-Deep Field through a fish-eye lens. It looked truly stunning. I told the story of how old they were and how very many galaxies there were in such a tiny, apparently empty patch of sky, as part of my introduction. But I was so nervous that day that Jenny, the manager, told me while showing me how to work the microphone: "And this is the 'off' switch, just in case you need to cough, or to throw up . . ."

(Anyway, I don't suppose it went too badly. When I popped back a couple of weeks later for a Telescope Amnesty event, alone, scruffily dressed, gawky and inconspicuous, I overheard one of the guests I'd talked to last time mentioning loudly that he'd been to my lecture. I was standing right in front of him but he clearly didn't recognise me, but he remembered my name! I was clearly luckier than an artist I'd read about once, who saw a noble lord and a museum attendant standing in front of one of his paintings. He crept up to them to hear what they were saying about it. He overheard the noble lord say, "Of the two, I prefer washing up.")

Lecture: What can we know about the Universe?

"We take it for granted," Russell Stannard said in a clear voice, "that science, by its very nature, is progressive and always will be." But it has not always been so; centuries have passed without many new discoveries in the past, and also our brains and experiments are limited in what they can achieve, so ". . . that process will one day grind to a halt." This does not mean technology, and what we can make, but what science itself is able to tell us. "The Universe will always retain an element of mystery."

There are many things that observation - and deduction where observations are limited, but secondary evidence is available - can tell us. For example, we know about our Sun, the planets, galaxies, clusters, and the expansion of the Universe. Apart from galaxies in our local group, of which there are about 30, all galaxies are moving away from us. If Galaxy A is twice as far from us as Galaxy B, then Galaxy A will move away from us at twice the speed. This means that the Universe is expanding in all directions.

We have been able to calculate from the speed of the expansion that the Universe is 13.7 billion years old. We know that increasing the density of a material such as a gas increases its temperature, and from that we can deduce that the Big Bang and the early Universe must have been terrifically hot - a fireball. There is observable evidence from that, namely the Cosmic Microwave Background.

(The CMB. Picture credit: startswithabang.com.)

We have been able to measure the chemical composition of the Cosmic Microwave Background, which is almost entirely hydrogen and helium, in a ratio of three to one (in mass, not number of atoms), and its temperature all around the three-dimensional perimeter of our vision, which is surprisingly uniform. It was an interstellar gas, not yet containing any stars.

We cannot look back to the moment of the Big Bang; we cannot say what caused it. To look back in space is to look back in time. But we cannot see the first 300,000 years of the Universe's existence, because no light could get through the cloud of subatomic particles. It was too hot for atoms to form, and the subatomic particles scattered the radiation that atoms can absorb. Theoretically, we could probe gravitational waves and neutrinos - but at least in present-day technology this is impractical.

How close to the Big Bang in time can we make direct observations? No closer - but we can study the features of today's Universe for clues.

One such clue is the (observable) Universe's homogeneity and isotropy. The Cosmic Microwave Background is remarkably uniform in temperature. For any material to be a uniform temperature throughout, it must have had some contact time to equalise. The nature of the Big Bang suggests that this was unlikely to have happened. In 1980, Alan Guth proposed that there was a very brief "quiet time" directly after the Big Bang, which caused connections between all the matter - such as it was - at the time. Expansion followed this later.

However, if this was the case, Hubble expansion predicts that galaxy clusters would not be in the place they are. The theory accounting for that is inflation. Inflation was very brief - lasting from 10 to the minus 36 seconds after the Big Bang, to 10 to the minus 34 seconds after the Big Bang (sorry for the lack of superscript font available!). This theory accurately predicts the density of the Universe.

(Diagram of inflation. Picture credit: universe-review.ca/R15-17-relativity.htm)

Many scientists have suggested alternative versions of inflation. The main questions to ask are: Are we sure it took place? And which type is right?

Before inflation began, the Universe would have had no volume, and therefore an infinite density. We call this a singularity. Physics cannot handle singularities - they should be impossible. Therefore, trying to talk about them doesn't really make sense. It wasn't just matter that was a singularity, but space itself. This means there was both no matter and space, and also infinite matter and space . . .

Stephen Hawking has pointed out that "time might melt away". You can't have space without time, or vice versa. So we may not be able to talk about the first instant of the Universe's existence at all. But is there an even stranger possibility?

Was there a singularity which exploded? If so - what did it explode into? Russell Stannard pointed out that we think of an explosion as, for example, a terrorist attack in which someone causes an explosion in a crowded area, causing carnage. That is because it explodes into something. But the Big Bang didn't do that. It created space. That space is still being created, and pushing galaxy clusters apart.

But space is nothing - how can nothing move the most massive objects in existence? For physicists, space is not "nothing". A lot goes on in it.

Einstein pointed out that space and time need each other to exist, hence relativity. Time deals with causes and effects. The Big Bang seems to have been an effect; what was its cause? A cause would have needed to have taken place beforehand - but there was no beforehand! The question itself has no meaning. Another question, which people have tried to answer for at least three or four thousand years, is: Why is there a world? Why does it remain in existence?

Why are there any laws of nature at all? Chaos calls for no explanation. ("Does it?" I thought.) Einstein seems to have stated that the most incomprehensible thing about the Universe is its comprehensiveness. To sustain life, the laws of nature have to be complex. Once the Universe undergoes "heat death", life will be impossible anyway. For a start, the Big Bang was very violent, and threw matter out a long way. If it had been less violent, the Universe would have shrunk and collapsed again quite soon, and we would not be here.

(Star formation in N90 in the Small Magellanic Cloud. Picture credit: the Faulkes Telescope Project.)

Another law of nature is called "g" - the strength of gravity. Gravity causes nebulae to collapse and stars to form. If g was larger, all stars would be massive blue supergiants and might only live for a few million years. We have needed four billion years to evolve, so we are lucky to have a smallish Sun which takes ten billion years to burn all its fuel. If g was smaller, nebulae would not clump together densely enough to reach the million degrees required to start nuclear reactions. (I disagreed with this and asked afterwards, what about more or less dense nebulae evening out the effect? Basically, if g was different enough, that just wouldn't work.)

The bodies of living creatures are very complex, containing heavy elements. Only hydrogen and helium could have survived the Big Bang; heavier nuclei would have been smashed up. Forming a carbon nucleus, for example, requires special conditions (more on that when I write a review of "The Magic Furnace" by Marcus Chown). In other words, heavy elements must be cooked in stars - and then they have to be got out of stars to make us! The way to do that is by a supernova. Supernovae are odd enough, because they are actually an implosion; how can an implosion trigger an explosion? It seems that neutrinos are what carry off all the matter - and neutrinos don't usually have the least effect on matter at all. It's likely that while you're reading this, a few thousand are going right through you. You could bounce a neutrino through the Earth from the UK to Australia 100 billion billion times before it had a 50% chance of knocking into an atom! They are very slippery - any more so and we undoubtedly wouldn't be here.

(Supernova 1987A. Picture credit: APOD.)

Planets could not exist in the early Universe: there are no planets around first-generation stars. ("What about gas giants?" I should have asked, but forgot.) Planets such as Earth are made of these heavy elements from supernovae, and form in secondary eddies around stars. Conditions for life are delicate. Russell Stannard quoted Freeman Dyson as saying, "The Universe knew we were coming" (it's up to you whether you agree with that, can't say I do . . .). The Anthropic Principle states that we're here because if conditions were any other way, we wouldn't be here to ponder them! Probability (or perhaps logic) leads us then to ask if there are really lots of universes, each with slightly different laws of physics, and we are in the one which is ideal to support life. We can't contact any other Universes, or prove there is a "multiverse" - if we could, they'd be part of this Universe. We also can't prove there isn't one.

Another thing science cannot tell us is how big the Universe is. We can observe things 13.7 billion light years away. But presumably anyone 13.7 billion light years away can see 13.7 billion light years further on. Where is the edge of the Universe? If we went to the edge of the galaxies and looked out into empty space . . . well, that would still be in our Universe. The current thinking is that it is infinite. "I, personally, am very suspicious of the word 'infinite'," Russell Stannard informed us, and went on to tell us a story about a hotel with an infinite number of rooms. The hotel filled up and did very well. So well that the manager decided to build another hotel with an infinite number of rooms. One night, there was a fire in one hotel. They got everyone out, but this infinite number of guests had nowhere to stay that night. They were all feeling in quite a fix until the manager told the infinite number of people in the first hotel to go to their door, look at its number, double it in their minds, and move all their possessions and themselves into the door they'd see. So the infinite number of guests outside went into the rooms occupied by the infinite number of people in the first hotel, and . . . er . . . I think the moral of this story is supposed to be "er".

Back to the Universe. What is its average density? This is an important question, because it decides the fate of the Universe. If it is dense enough, gravity will halt its expansion. It may stop forever and remain static, like a craft in orbit around the Earth; or, if it's a bit denser than that, the galaxies will fall back together, like a football falling back to the pitch, and a "Big Crunch" will occur one day. But if the Universe isn't dense enough for this, it will go on expanding forever.

It seems that matter itself - stars, gas, etc - make up 5% of the density we need for this to happen. Dark matter accounts for more: 28%. (Science may one day tell us what dark matter is, but we have no way of finding out yet.) Our own local group of galaxies should hold together. The violence of the Big Bang was not enough to pull them apart. Not on its own.

The remaining ~70%* of the "critical density" is dark energy. It adds up perfectly to sustain a critical value (which Russell Stannard seems to find very satisfying, while I find it rather bewildering - doesn't it change?). Not all matter was created during the Big Bang, perhaps. Inflation may have created more. Space expansion creates matter . . . But it looks as if the Universe will expand forever. Look back at the inflation picture. The expansion seemed to slow a little somewhere in the middle. Without dark energy, we would fall back together. But dark energy somehow manages to create more of itself all the time - and it pushes the galaxy clusters apart.

(* Yes, you nitpickers, I have spotted that 5%, 28% and 70% add up to more than 100%. I'm afraid that's what I've got written down in my notebook. I don't remember why. We can make some educated guesses . . .)

Why would a vaccuum have a mass (or an energy)? There's a lot going on in it (virtual particles and antiparticles colliding - Hawking radiation - sprang to my mind). The expansion of the Universe is now actually speeding up, just as populations increase exponentially - the more dark energy is created, the more can be created! Dark energy repels, and repulsion vastly increases with time. The calculated value of expansion is 120 orders of magnitude greater than what we observe, which Russell Stannard describes as "embarrassing" (and "BANG!" describes as the probably the greatest ever discrepancy between the observed and the predicted!). Could a mechanism we don't know about be at work? We don't know.

Is there a connection between today's repulsion of clusters and the early inflation?

One final question: is there other life in the Universe? Exoplanets seem to be being discovered every day; but they are too far away to visit. Where do we rank with ET? The brain size has increased at three times the rate of body size in humans. But Russell Stannard does not believe ET is findable, and they will have to contact us. He also said that the human brain is not designed to do science, but to hunt, gather, find mates, ward off predators, etc - so it's actually a huge achievement that we've got where we are today at all.

We are hugely privileged to be living in the scientific age, he concluded. The human race has existed without being in the scientific age for thousands of years. One day, all that can be discovered will have been. That doesn't mean we'll know everything, but we'll have come up against all our limits of science. But right now we're in the middle.



Afterwards Jenny gave us a 15-minute planetarium show, incorporating a lot of three-dimensional graphics from our beloved SDSS. According to her show, the Universe is 92 billion light years across. There was a five-minute interval during which Russell Stannard was surrounded by a crowd of children. Good on you all, I thought from my seat. I hope they grow up to be interested in science forever.

As we filed out I couldn't resist going and bothering him. I thanked him for the lecture and told him I'd been an Uncle Albert fan for about 17 years - though I'd never got over the heroine Gedanken saying she was giving up. He merely smiled. His writing is very exuberant and I thought he'd have something to say. He didn't. He was very quiet: perhaps he'd heard it all before; perhaps he was tired, in which case I hope I didn't tire him further. (He did sign my Uncle Albert books, though!) But I feel very privileged to have finally met someone who made such a difference so many years ago. I hope I've done his talk justice.

5 comments:

Jules said...

Excellent notes Alice. Thanks for taking the time to write and post them. And nice use of supernova 1987A. :)

Half65 said...

Thanks Alice to share this with us.
I made a first look but I need time to read in deep.
Great post.

Jenny said...

Alice, thanks for the write-up and I'm glad you enjoyed the lecture. It was definitely one of my favourites of the series.

The rainbow lights came from a row of LEDs hidden under the horizon line. And I hope I said that the *visible* Universe is 92 billion light years across. I wouldn't claim to know how big the whole thing is :)

John Cosier said...

Great set of notes!! I'm impressed by your note-taking skills!
Just to clarify a couple of tiny points, in the infinite hotel, going to 2 x room number leaves all the odd numbered rooms free for another hotel-full of guests.
Also, my recollection is that the numbers were 5%, 25%, 70%, suspiciously round so I guess an estimate of the actual proportions!.
John.

weezerd said...

Thank you Alice, excellent set of notes giving a good impression of the lecture.