Parallel Universes

Scientific American ^ | May 2003 | Max Tegmark

[FractalMan]

A few weeks ago, I listened to a program on the radio about the Multiverse (humm, I wonder if that really should be plural). Anyway I began to think about it in the context of the universe that we live in. What is it that keeps us synchronized? Those around me have common understandings of history (except for the liberals who always want to re-write it - sorry had to get a political statement in somewhere). We are able to communicate and understand each other because we are synchronized in our universe.

But then I found myself having a really bad week. My decisions at work weren't right, those around me had difficultly understanding me, I would try to do things around the house and all I would do is make it worse. Then I realized that maybe I was out of sync with this universe! Could it be? Still the question remains, what keeps us and our universe synchronized?

[thirdheavenward]

If you start getting frustrated, just let me know. We can drop this at any time. However, for myself, I don't get a chance to dialog about this stuff very often, so I get a kick out of it.

>>Assumption: The universe was infinite in extent at the big >>bang, just as it is infinite in extent now, but it was >>just a lot smaller back then.

>I don't think you can make that assumption.

Well, why not? An assumption is a thing you just make, so that you can make further progress in some train of reasoning/thought. If you mean, in contrast, that the assumption doesn't make sense, then please explain why the total integrated volume of the universe at some very short time after the Big Bang could not have been infinite. I like a model which is finite the whole time, but a non-finite model seems consistent too.

>Let's see whether I can clear this up. Back it off a >dimension, and consider the "hyperverse" to be like the >surface of a balloon. Our Hubble volume ("universe") is >like a tiny circle drawn on that balloon. The balloon has a >radius, and the circle has a radius, and it seems like you >might be confusing them. If I say "infinite volume", I'm >referring to the area of the balloon, not the area of the >circle.

OK, I'll back off a dimension. I could draw a circle on the ballon (assuming it was rigid), and then cut the circle out. I could use a marker to draw a smaller circle on the curved circle that I cut out, and call that little circle the "Hubble Volume". The piece I cut out still has the same curvature as the balloon, but it doesn't correspond to the radius of either the circle I cut out, or the smaller "Hubble Volume." We are in a situation where we don't know the radius of the cut out, but we do know the other two radii. There is a certain elegance in just assuming that the area of the cut-out is equal to the area of the whole balloon, but I naturally can't see why it is necessary.

[thirdheavenward]

That's what I'd like to know!

[Euro-American Scum]

Just think. There are universes in which Jane Fonda makes endless sequels to Barbarella.

And there is a universe where Hillary Clinton is President of the United States. No, wait. That could be this one in a few years.

[Physicist]

Well, why not?

The Hubble expansion is proportional to distance. It doesn't matter whether you are talking about a point three light years away or three quintillion light years away; they will all extrapolate back to the same single point at the instant of the Big Bang. (That's the mathematical idea, but in practice, I wouldn't carry any of these extrapolations back before the Planck time. What I'm saying is that it's not necessarily true that the multiverse started out infinite, so we can't just assume it.)

then please explain why the total integrated volume of the universe at some very short time after the Big Bang could not have been infinite.

A short time after the Big Bang is a whole 'nother kettle of fish. The universe probably was infinite at that point.

OK, I'll back off a dimension. I could draw a circle on the ballon (assuming it was rigid), and then cut the circle out. I could use a marker to draw a smaller circle on the curved circle that I cut out, and call that little circle the "Hubble Volume".

I don't understand. What does the cut-out physically represent? The edge may not cross within our Hubble volume, but it crosses within somebody's Hubble volume. What happens when they come up to it? What sort of object is it supposed to be?

[thirdheavenward]

If you want to travel intergalactically, you had just better figure out how to go faster than light, because most of those galaxies are growing farther away faster than that.

As for travelling somewhere close, like Andromeda, (only 2 million light years), or Cygnus (a mere 30 million ly), even sub-light you still need some pretty awesome tech, because interstellar space is bad news for our kind of life.

Your first problem is freezing yourself or regenerating yourself. Freezing is difficult because even jumping in liquid He won't freeze your insides fast enough to prevent ice crystals from forming (the outside will insulate the inside too much). Frogs - easy, people heads - hard. But maybe you could just sleep and have the robots replace your body parts and neurons one by one as they go bad over the millions of years of travel.

The real reason I wanted to reply to you, though, is that there IS friction in space - just not much! But if you want to coast 2 mil ly, it doesn't take much friction to stop your journey. The only plausible solution to that I have heard is to collect interstellar hydrogen as you go, and use that for fusion fuel, but that will also slow you down to 1/3 speed of light.

[Arthur Wildfire! March]

Regarding kryogenics, that is in its infancy. I am certain that more advanced versions will develop. You have a point about computer parts replacing body parts. That might be a more practical way to go.

"The real reason I wanted to reply to you, though, is that there IS friction in space - just not much!"

We know there is friction in our galaxy. But what about the gaps between galaxies? Do we know much about them, yet? Are we able to see them? Are there pathways in them that are essentially friction free? And, there probably would be significantly less gravitational pull. So, travelling in those gaps could be a thousand times less difficult than it seems right now. And, the perceived difficulty will continue to plummet more quickly than we realise, especially when we learn that light as we know it is merely a residue of something that moves much faster. [Just a scripture-related hunch on my part, since God has a power beyond our comprehension.]

[Prodigal Son]

Your first problem is freezing yourself or regenerating yourself. Freezing is difficult because even jumping in liquid He won't freeze your insides fast enough to prevent ice crystals from forming (the outside will insulate the inside too much). Frogs - easy, people heads - hard. But maybe you could just sleep and have the robots replace your body parts and neurons one by one as they go bad over the millions of years of travel.

This whole problem can be sidetracked by developing a way to upload a human mind into a computer and simply putting the computer in sleep mode until it comes close enough to a star to achieve a sufficient energy supply for operation. In essence, instead of having robots replace body parts, you'd basically be a human mind in a robot body yourself. The vast distances and times wouldn't matter to a machine that was asleep.

For all intents and purposes, no time would pass for the computer even if it took a million years to get where it was going (assuming the physical properties of the computer/machine didn't degrade over time).

[ChicagoHebrew]

I was just thinking that this explained the Nazis in space on Star Trek.

Actually, if I remember correctly, the "Nazis in space" happened when a Human crash landed on a planet and somehow became the planet's leader. He thought he could use the Nazi's methods and imagery to promote efficiency and unity among the planet's people, without the evil warmongering bigotry. He was wrong. Ok, I am a total dork.

[Twinkie]

I did read this article in this reality, but maybe "I"
didn't in that other one. In which case, the I in that
other reality is not as confused as the me in this one is
and is eating a bowl of Moose Tracks ice-cream right about
now - in which case has gotten ahead of me here and is
already on the second bowl. Gotta run!