Space the final Frontier (and how many aliens know we are here)

“So where are we now?”

Looks like space to me, about fifty two liight years from earth.

"Not much going on around here is there?"

Of course not, that's why they call this place space. If space wasn't empty it wouldn't be called space, would it?

“I thought we were meant to be in the middle of a galaxy?"

We are in the galaxy but not quite the middle of it. We’re flying along one of the spiral arm of a galaxy. Like most galaxies, this galaxy that the earthlings call the Milky Way, has a central glob of stars surrounded by spiral arms because the whole galaxy is spinning.

"So shouldn't space be stuffed with stars if we’re inside a galaxy? There seems to be lots of stars but not many of them are near here.”

That's the way space is. The stars are spaced out by huge distances but because space is so large there are a lot of them. Thinking in terms of the size of people will make it easier to imagine the distances. The earth's sun is just under a million miles across but imagine the sun as a person of normal height. At this scale the whole earth would be the size of a marble. How far away do you think the nearest star would be?

“I'll guess a million miles.”

Not quite that much, just over thirty thousand miles.

"That's not far."

It's far enough. One person every thirty thousand miles hardly makes a crowd does it? It would take you four hundred and fifty days to walk that far even if you never stopped or slept. The stars in a galaxy only fill up one thousand billion billionth of a percent of the space. The other 99.9999999999999999999999% is empty.

“OK, I see now why this place is called space. But there are still lots of stars out there. How many stars are there in total?”

All the stars you can see are located in this galaxy, the milky way. Looking out you can see only a few thousand stars but there are a 100 billion stars in this galaxy alone. There are probably as many galaxies in the universe as there are stars in our own galaxy so that would make about 10,000,000,000,000,000,000,000 stars.

“That makes the little marble sized earth I was thinking about seem pretty insignificant.”

Small but because you live there it is significant and precious to you and everyone who lives there.

“So what's happening on Earth right now?”

That's a very interesting question.

“It seems a simple question to me.”

Yes but the simplest questions are often the most interesting and far from simple.

“But simple would be good right now, I've only just recovered from thinking about relativity.”

Well here is one last thought for you on relativity. At this very moment everyone on earth is in the year 2007 but as far as we are concerned they are still back in 1955. Also if earthlings were looking for us in a powerful telescope then they wouldn't be able to see where we are now until the year 2059.

“Sorry, I'm not getting this Albert. Is this because we are travelling so fast again?”

It comes back to the speed of light but it is just because we are so far away. If nothing can travel faster than light, then events happening a long way away can only happen in the past. Imagine we were standing where we are now fifty two light years from earth and the world suddenly blew up. What would we see?

“The explosion I suppose.”

But as we are fifty two light years away from Earth, we wouldn't see the explosion for fifty two years. So if the Earth had blown up five minutes ago we wouldn't know or care because there is no way it would affect us.

“I think I'd care if I called home and discovered they were all dead.”

Yes but it would take 50 years for the message to reach earth, no radio signal or telephone call can travel faster than light remember. Imagine it was just a bad dream and the Earth hadn't blown up. It would also take another fifty years for any message to travel back, so if we stayed here it would be a 100 years before you would know for certain that the Earth was still there.

“OK. I think I get that.”

So at this distance anything that happens now on Earth can't affect us for fifty years and anything we do here can't affect earth for fifty years. When an event happens anywhere in the universe any possible consequences start spreading out like ripples through space at the speed of light. Until light or any signal from that event reaches a certain point in time and space, it is as if it never happened. This is perhaps the most important lesson from relativity. Don't worry about things that can't affect you or things you can't influence.

“So has anything from Earth had any impact out here?”

For most of human history, nothing man has done has had any impact on the cosmos but that is changing. As soon as radio and television were invented and the signals were strong enough to be broadcast around the world, news that humans existed has been rippling out through the galaxy at the speed of light. About fifty years ago the Earth would have lit up like a light bulb in terms of radio and television broadcasts leaking into space.

“Wait a minute wasn't that flying saucer at Roswell discovered fifty years ago?”

A little bit more than fifty years ago, that was in 1947, if it happened at all.

“You don't believe in UFO's?”

If it was an alien space ship it must have been lost because it's very unlikely they were looking for us. Even if there are aliens in the galaxy, most of them wouldn't yet know that we exist. The bubble of radio and television signals from Earth will only have reached the few thousand stars that are within fifty light years. Of the 100 billion stars in the universe only 0.000002% could possibly know we exist. It will take another 150,000 years for the whole galaxy to be able to detect the earth's radio signals, so in the next half million years or so aliens might coming knocking on the door. What has just reached us in this part of space is the news of the death of a famous scientist back on earth.

“Who?”

You may have heard of him, Albert Einstein.

“You've just died?”

On the Earth of 1955 I have, but death has a very bad reputation. I have always felt that the fear of death is the most unjustified of all fears. After all, once you are dead it can't get any worse so logically things can only stay the same or get better.

“So you're not dead?”

If the character in a novel, who has never lived, can be brought to life just by the imagination of the reader, how much easier must it be to keep a real person alive through remembering their words and deeds.

“Are you sure about that?”

Dead certain. I'm here talking to you aren't I?

To Relativity and Beyond

“So what happened when you first proposed your theory of relativity.”

A deafening silence. I was still working at the patent office when my special relativity paper was published in 1905 and no-one seemed particularly interested at the time.

“You weren’t immediately famous?”

Not at all, I wasn’t even an established scientist at the time. I was a poor patent clerk trying to claim that the greatest mathematical genius of the world Isaac Newton was wrong. It was lucky I wasn’t locked up for being crazy. But a few well known scientists did take an interest. Max Planck and one of my university mathematics teachers, Hermann Minkowski, did believe in my ideas. I am ashamed to say that I skipped a lot of Minkowski’s lectures, but it was he who helped transform a lot of my ideas into solid mathematics in a paper he published in 1908.

“Three years later? Had nothing happened before that?”

Oh there was a little bit of interest. I tried to use my relativity paper to get a university job in 1907 but they wouldn’t accept it. I ended up using a paper that helped prove the existence of atoms and molecules.

“You invented relativity, started quantum mechanics and discovered atoms? When did you find time to do all that?”

All in the same year, 1905.

“Wow. But they knew about atoms before then surely?”

As an idea yes, but a lot of people doubted atoms were real. How can you believe in something that is too small to see?

“How can you believe in things you can’t see?”

By looking very hard at things you can see and using a little imagination. Eighty years earlier botanist called Robert Brown who was looking at grains of pollen in water through a microscope.

“The things that cause hay fever?”

That’s right they are so small they almost float in the air but in water Robert Brown saw that they seem to jump and jiggle around like they are possessed. This is called Brownian motion. Well I looked at the pattern of the jiggling and showed mathematically it made sense if the pollen grains were being constantly bombarded by smaller particles. If you put the pollen in pure distilled water, what else could those smaller invisible things be?

“Water atoms?”

Water molecules, which are made up of three atoms two hydrogen H and one oxygen atom O which is why water is called H2O.

“Neat. So go on, tell me when did you get famous?”

Does that really matter? A lot of people are famous for nothing at all these days. Isn’t if better to be not famous but have achieved something truly important?

“I suppose, but you did both. Isn’t that why you are here explaining all this? So what made you world famous?”

What made the world really take notice was when other people started showing that my crazy ideas seemed to right.

“Wasn’t that your job, to prove your theories?”

I could have but I was a much better thinker than a doer. But before I tell you what happened to make the world really take notice, I have to tell you about general relativity, the full version.

“Oh no, I was enjoying just chatting. Will this be harder than the special relativity you told me about last time?”

It won’t be harder for you, but it was much harder for me.

“Why?”

Because I was trying to bring together my ideas of relativity and create a new theory of gravity all at the same time. The mathematics of general relativity is very tricky and took me more than ten years to get right, but the ideas aren’t too scary. The basis of my idea of gravity should be known to anyone who’s ever been in a lift.

“A lift? How come?”

When a lift moves up suddenly you feel heavier and when it starts to fall you feel lighter. Now what happens if you are in a lift and the cable breaks?

“You fall and die!”

Eventually but while you are falling you will be weightless. Where has gravity gone?

“I don’t understand.”

If you are in free fall you feel weightless, until you land of course. So I realised gravity is just the same as acceleration. Imagine you were floating in empty space without gravity but trapped inside a lift and a passing spaceship grabbed the lift cable and starting accelerating. You wouldn’t be weightless anymore, you could stand on the lift floor. You would feel that up was the direction you were being pulled in.

“OK, but why is that such a big thing?”

It was a huge realisation because it allowed me to create a new theory of gravity. Isaac Newton worked out a mathematical law but it didn’t explain how gravity worked. When I worked out all the details I realised that gravity works because objects, any object bends space. The bigger the object the more space gets bent.

“Here we go again.”

It’s not that hard I promise. Imagine space as not as some solid thing but a stretchy rubbery thing.

“OK.”

When there is an object big enough to create a strong gravitational pull, it bends space just like a heavy metal ball on a trampoline or you on a trampoline. Now if you put a marble on the edge of a completely flat trampoline what would it do?

“Just sit there I suppose.”

Exactly. Now if gently lowered you onto the centre of that trampoline what would happen.

“I’d dent in the middle bit.”

And….

“The marble would roll in to the middle?”

Now you’ve got the idea and that’s how I thought gravity works.

“So does it?”

Well that’s what got me famous. Gravity is supposed to pull together things that have mass, physical things. Light doesn’t have mass, it doesn’t weigh anything so it shouldn’t be affected by gravity, but if gravity bends space then a light beam should get bent with it. I predicted that gravity from the Sun should make light bend by a certain amount.

“How can you show that?”

Well it needs the light beam to be going right past the sun. When the Sun is blocked out by the moon in a total eclipse, the sky goes dark and the stars are visible for a few minutes. This is the only time you can see light from a distant star skim past the edge of the sun. If my theory was right then the stars nearest the Sun should appear to be shifted from their normal position because the gravity of the sun had distorted the bit of space the starlight was coming through. In 1919 an expedition led by an Englishman Arthur Eddington travelled off to Principe Island to study an eclipse the results seemed to agree with my theory. If I've planned things right we might I be able to demonstrate how this really happens.

“How about the ideas about time changing as you speed up? Has anyone shown that really happens?”

That has been tested too but that took a lot longer. It is not easy to find clocks travelling close to the speed of light after all. But fortunately there are natural clocks in the universe. The decay of radioactive atoms, where unstable atoms breakdown usually into smaller ones, is one of them. This is the sort of clock used to work out the age of objects in carbon dating because radioactive decay is like the tick of a clock. The carbon-14 clock ticks very slowly if a bit randomly over thousands of years as it decays into a different atom nitrogen-14, in 5,730 years half of it decays. Carbon-14 in the air is taken up by leafs and gets made into wood in trees and anything else that plants make. By measuring how much of that carbon-14 has decayed scientists can work out how old a piece of wood is, even if it is tens of thousands of years old. Another sort of natural clock is seen in unstable subatomic particles called Mu mesons which last only a millionth of a second or so before breaking down. This is a super fast clock. These particles are made in the top of the Earth's atmosphere by collisions between cosmic rays and atoms in the air.

"What are cosmic rays?"

They are particles like us that come from stars and fly across the galaxy at huge speeds until they collide with something. When they hit the atmosphere of a planet they smash into atoms in the air and produce a shower of particles and atomic remnants. Meson particles are created by these collisions at the edge of the Earth's atmosphere then they shoot onwards to the Earth's surface at 99.5% the speed of light. Even at this speed a millionth of second shouldn’t be long enough to reach the ground before they break up or decay.

"So they never reach the ground?"

That’s the interesting bit, so many mesons reach the ground that they must be surviving roughly ten times longer than they should. At 99.5% of the speed of light how fast do you think time passes?

"At a guess I'd say about ten times slower."

Exactly. Relativity may seem bizarre but it also seems to be true. It’s not just speed that slows down time. In general relativity I discovered that gravity slows down time as well. I was very excited to read that in 1971, sixteen years after I died, J. C. Hafele and Richard E. Keating proved the effects of speed and gravity and time by flying four atomic clocks in opposite directions around the earth and comparing it with a clock on the ground.

“How much did the clocks change by?”

It was only a difference of three hundred billionths of second but the planes weren’t going very fast and it was almost exactly what relativity predicted. To get big effects you need a lot of gravity. Remember we talked about black holes a while back?

“Oh yeah, where gravity is so strong that light can’t escape.”

Well if you saw someone fall into a blackhole from a safe distance they would seem to hover forever at the point of falling in, just before they disappeared from the universe, because time was slowed down so much by the intense gravity.

“What would they see looking out?”

They would be able to see the rest of the universe seeming to speed up. Rather than seeing their lives flash before their eyes, they would see the whole future of the universe unfold in fast forward.

“Wow, that’s freaky….Albert, I hope you don’t mind me saying this, but the Internet is full of nutters who claim you were wrong. I know you’ve explained to me how relativity explains lots of things but is relativity the final answer?”

Isaac Newton’s theories lasted twice as long as mine have so far. Who knows how long my theory will last, perhaps one of those nutters as you call them might be right. A hundred years ago I was just like them, trying to overturn hundred’s of years of tradition and convince people who thought that the answers to all the big questions had already been discovered.

“Have all the big answers been discovered?”

Not at all, not then and not even now. I spent almost forty years of my life trying to work out how quantum mechanics, gravity and relativity could all work together into one great theory of everything and failed. But I died convinced there was a way of tying everything together, God’s blueprint for the universe. So I’m certain a better theory will be discovered one day.