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?