Bang, stretch, twang, crunch — Spaceship Earth approaches the gaping black hole!

Press, 5 September 1981, Page 15

Bang, stretch, twang, crunch — Spaceship Earth approaches the gaping black hole!

. “Ah. what ' is man? Wherefore does he why? Whence does he whence? Whither is he whithering?" — Dan Leno, music hall star.

Thus has humankind pondered since the night one of our ancestors fell out of a tree and looked up to see for the- first time, those glittering heavens and infinity instead of green leafy stuff. Broadly speaking, in the beginning was the Big Bang. At the moment we're doing the Big Stretch. In the end we’ll have the Big Twang followed shortly thereafter by the Big Crunch as the universe zaps down a black hole into nothing.

And if the black hole doesn’t get us the proton decay surely will.

:This interesting scenario ' has been imparted to thousands of fascinated readers by the British popular science author and physicist Professor Paul Davies. Professor Davies is now back in his Chair of Theoretical Physics at the University of Newcastle-upon-Tyne after four weeks as Canterbury University’s visiting Erskine Fellow.

"'One way or the other the present condition of the universe has got to chnge and there are really only two possible outcomes,” says Professor Davies. "One — the universe will continue to expand forever and everything in it will run down to a state of total disorder. Or two — the universe will eventually slow up and stop expanding and then recontract until it reaches the Big Crunch, the Big Bang in reverse.” Let’s take the Big Crunch grand finale first. Our sun is middle-aged at about 5000 million years. Without going into too much detail, ■ the culprit in bur suns eventual demise — and ; that of all stars — is gravity. .-, One day the huge pressure at the core of the sun s

furnace will run out and no longer push against the sun’s huge inward force of gravity. “The sun will eventually implode down to a white dwarf. It’ll be compressed down to the size of the earth and it’ll just sit around doing nothing," says the professor. Earthlings won’t get just a grandstand view of this. As the sun’s core crashes inwards the outer layers will explode outwards and probably engulf the Earth’ More than toes will be toasted.

“Bigger stars tend to collapse more violently and become neutron stars," says Professor Davies. "They are much smaller than other dwarfs, about the size of Christchurch. With the neutron star’s matter totally crushed, even the atoms themselves collapse."

The Crab Nebula in the Constellation of Taurus has the remains of such an explosion. It also has a pulsar, a neutron star so dense that it can rotate up to 30 times a second and sent out pulses of radio waves .rather like a lighthouse.

"Even more extreme is what happens if the star is a little bit bigger again. It will collapse so violently it forms a black hole. A lot of things we say seem like science fiction but really science fact is stranger.

“At the ultimate crunch the star will literally shrivel away to nothing. This totally collapsed star is called a singularity and the empty space around it is the black hole."

The black hole is caused by gravity, which on collapsed stars is greatly distorted. On a white dwarf your average teaspoon would weigh about one million tons. On’a neutron star it would weigh about 1000 million tons.

At a singuarlity gravity becomes infinite. Light is trapped around it to become a black hole, time is trapped and reversed, laws of cause and effect break down,and matter is annihilated.

“A black hole is certainly a one-way ticket," says Professor Davies. “You can’t come back out again. If you went there you wouldn’t think you were actually falling into a hole. It’s only from a long way that it has meaning.’

"Anything that falls into the black hole gets sucked into the singularity and then presumably leaves the physi-

By

KAREN MANGNALL

cal universe. That’s why a singularity can be thought of as the edge or boundary of space and time. It's a nonplace.” Time and space, in physics, are inseparable. Spacetime can be stretched, shrunk and twisted like an infinite piece of chewing gum. At a singularity, spacetime. is ripped open. Science fiction is fond of speculating that if you fell into a black hole you'd whizz through the singularity into another parallel universe. “I believe, and I think I speak for most of my colleagues, that talk about other universes and other regions of space which can be entered through black holes is not realistic," says the professor. But on with the story. The known universe has so many billions of stars, millions of them old and big enough to have run out of steam by this time, that there must be many black holes lounging around. “There is probably a black hole in the middle of our galaxy now. It would perhaps be a million miles across.” Professor Davies says. “If they literally bang into each other they coalesce to form a bigger hole; they eat each other and combine and can’t separate. "Black holes attract nearby stars. Over the immensity of time one might imagine that some of the stars will sink to the middle and others will be thrown off the very edge of the galaxy. “Eventually the combination of the stretching of the universe and black holes gobbling each other could lead to the Big Twang as spacetime and matter rocket into a giant black hole in the Big Crunch.

"ine big Crunch will happen before any of the others. With proton decay we’re talking about tens of billions of years hence." Protons and their opposite numbers, electrons, make up atoms. Protons decay, on the average every 10 followed by 33 zeros years, to form positrons. Positrons are positive electrons also called antiprotons. Positrons are also anti-matter. When a positron meets an electron they annihilate each other to produce lots of very shortwave red light called gamma rays. Billions of years hence, barring the success of the Big Crunch, the universe will decay into positrons and electrons which will bump into each other and wipe out. Whereas the Big Crunch will be the terminal burp, proton decay will be The Night of the Billion Hiccups. “But not all of the positrons and electrons will meet because the chances of encounter fall as the population gets destroyed,” says Professor Davies. So in the end (lovely thought) there will be an infinite soup of gamma rays witn a tew stray noodles of positrons and electrons wandering lonely through that endless night. But proton decay • has a more creative side and can illustrate what would have happened tiny fractions of a second after the Big Bang. "The decay of protons opens the road to explaining how the universe we know is made up of matter rather than equal amounts of matter and anti-matter, which theoretically should have been the result of the Big Bang.” An experiment this year showed that for every 10'

billion positrons there are 10 billion plus one protons. Multiply this difference by the huge number of these subatomic particles rushing about after the Big Bang and it becomes quite significant. “So as the universe cooled off after the bang the protons killed off the anti-protons (positrons) and left the residue of extra protons." The gamma rays now wandering about the universe are relics of that primeval annihilation. About one second after the Big Bang the temperature dropped from infinity to about 10 billion degrees and all the anti-matter was destroyed. As the temperature dropped the lighter elements like helium and hydrogen were formed. After about four minutes nuclear reaction switched off. Only after 100,000 years did the temperature fall below 5000 degrees Celsius. “During that time the universe was a glowing fog of hot plasma,” says the Professor. How the universe got from plasma to today’s solid structures is not fully understood. “But one thing is clear, if some of this material concentrated in one place then additional gravity would make it accumulate more material from the environment. "Random process means that some regions acquired more matter which could accumulate to become protogalaxies. Given the expansion of the whole universe plus the local contraction of matter into these blobs, the gaps between blobs would become almost entirely empty. "Then the huge blobs contract and become fragmented which could lead to the formation of stars like our sun.”

But somehow I always liked the one that went: “In the beginning God created the heaven and the earth It had wossname, romance. Which brings us to the inevitable question of . what went “before” the Big Bang? What caused it? Nothing, says Professor Davies, because if we follow the Big Bang right back to its beginning we find the future universe at infinite density and in zero volume. We come to a singularity similar to the end point of a collapsing star, but in reverse. We also come to a naked singularity. Nothing for Patricia Bartlett to worry about, just nature’s little anarchist. A singularity uncloaked, no longer hidden from the ordered universe by its black hole. “The presence of a naked singularity destroys science by allowing things to happen without a lawful pause — indeed anything may happen in the vicinity of such a singularity," says the Professor. “We can now view the creation as a special case of a naked singularity. Anything can come out of- a naked singularity — in the case of the Big Bang the universe came out.” If the Big Bang singularity is the final past boundary of all the physical universe, then time itself began only at the Big Bang. "The point about knowing the ultimate fate of the universe is its philosophical impact. We all live our lives by some sort of cosmological framework even if it’s based on a flat earth or an unending universe. If we want to come to an understanding of it at all, especially the fate of human beings and their place in this, we must understand how the universe started and how it will end.”