Space

[BomberGal]

Probably, but I guess it depends on how you characterise life... if there is energy there, perhaps it's not inconceivable that something could make the most of that energy... who knows?

Well, you're right, who knows indeed. But you need atmosphere to have life, and I can't really imagine there being an atmosphere in planets near a black hole. Life requires more than energy.

 

[deeman12]

Who cares about space, we have everything we want here. We dont want to go space and have sex with aliens, i rekon we stay and enjoy KFC.

 

[Higgs Boson]

Well, you're right, who knows indeed. But you need atmosphere to have life, and I can't really imagine there being an atmosphere in planets near a black hole. Life requires more than energy.

Life as we know it. Knowing what we do about the universe, ie bugger all, it's certainly possible there could be forms of life that we cannot even comprehend. In the same way that 500 years ago humans couldn't conceive of microscopic life.

Pure speculation, though, and probably fairly pointless eh? I doubt we'll ever find out.

 

[BomberGal]

Life as we know it. Knowing what we do about the universe, ie bugger all, it's certainly possible there could be forms of life that we cannot even comprehend. In the same way that 500 years ago humans couldn't conceive of microscopic life.

Pure speculation, though, and probably fairly pointless eh? I doubt we'll ever find out.

Biology has advanced just a touch in the last 500 years!

Biology is fairly reduce-able in what you need for life, no matter where you are in the universe. Replication, structure, solvent, atmosphere. How a given life form gets around these problems is where evolution comes into play, and is what we can't conceive, but realising that life needs these is a little different from conceiving the idea of cells.

It also depends on how you define life. Biology defines it as something that is capable of reproduction (requires replication), growth (requires replication and metabolism), and response to stimuli and pressures. This subsequently defines a necessary set of molecular elements. Life necessarily depends on its environment, therefore we must have a minimum environmental requirement.

By this definition, viruses are not life-forms. Perhaps there are virus-equivalents on other planets - we have no way of conceiving how these might work, but it's not really 'life'.

Philosophically we can't say we know, but as a biologist this is just my opinion.

 

[Higgs Boson]

Biology has advanced just a touch in the last 500 years!

Biology is fairly reduce-able in what you need for life, no matter where you are in the universe. Replication, structure, solvent, atmosphere. How a given life form gets around these problems is where evolution comes into play, and is what we can't conceive, but realising that life needs these is a little different from conceiving the idea of cells.

It also depends on how you define life. Biology defines it as something that is capable of reproduction (requires replication), growth (requires replication and metabolism), and response to stimuli and pressures. This subsequently defines a necessary set of molecular elements. Life necessarily depends on its environment, therefore we must have a minimum environmental requirement.

By this definition, viruses are not life-forms. Perhaps there are virus-equivalents on other planets - we have no way of conceiving how these might work, but it's not really 'life'.

Philosophically we can't say we know, but as a biologist this is just my opinion.

Agree with everything you say.

Particularly your first sentence, and this is, I guess, what I'm getting at. Biology has advanced in the last 500 years, by heaps! We now know a hell of a lot more, and our understanding is far more sophisticated. But, if we can keep ourselves from self-destructing through the end of the oil age and manage to continue to avoid global catastrophes, imagine what we'll know in another 500 years as our understanding of things such as quantum mechanics and multi-dimensional physics develops.

For instance: dark matter. We know stuff all about it, except that it's demonstrably there, and in massive volume. Could there be life of a type existing amongst it, feeding off it, equally invisible to us? It's well possible that there's things out there that our brains, developed over millenia to process just four of the multi-dimensions apparently out there, couldn't even physically conceive of.

It's a very interesting train of thought!

 

[BLUEBOY1]

It's difficult to know whether space is infinite in extent. All we can say for now is that it's very, very big. It appears to be 13.7bn years old (I say appears because if inflationary theory is right, it is much older and perhaps infinite in age), so we can only see things that are within about 13bn lightyears from us, because that's how long the light has had to travel. This region is called the visible universe.

For various, slightly technical reasons, it observationally appears to be the case that the full universe is vastly huge compared to the visible universe, and a lot of theories would also point in that direction. Particularly Inflation, which would have many, many regions of space with different physical laws/constants, each region probably a lot bigger than the visible universe. Alan Guth, who originally put the theory forward, estimated the full universe as at least 10^23 times the size of the visible bit, but I'm not sure how he came to that.

Personally, I don't like the idea of an infinite universe, but it could well be.

In terms of reaching an end... I'd be very confident in saying that wouldn't happen. If the universe isn't infinite, then we would expect it to be shaped as the surface of a 4-dimensional analogue of a sphere. This is difficult to visualise, but the point is that on the surface of a sphere, if you keep travelling, you get back to where you started. The same would be true of space. The universe would be finite but unbounded.

As for the question of what space is, that is very difficult, and the answer is not yet known. Our view of space has changed a lot since the days of Newton, when space was considered just an arena for things to happen in. Now it's considered dynamic, interacting with the matter in the space, and fundamentally tied up with time. Maybe if we can tie general relativity in with quantum we'll get a better understanding, but for now, that's a toughie.

Guesses about how common life is are enormously speculative. I'd like to think that it is reasonably common on planets where it can exist, but I am sure that there is life out there, and because of the vastness of the universe, there is a lot of it. In fact, the only reasons I can think of for doubting the existence of extra-terrestrial life would be religious ones. However, the United Federation of Planets is probably precluded by the enormous distances involved, definitely under our current understanding of physics. But it would be nice to know that we weren't alone.



Almost certainly won't happen. I say that because of the surprising fact that the vacuum has a density. In fact, 73% of the density of the universe is contributed by the vacuum (along with 4% from everyday matter and 23% from dark matter). This has the effect of accelerating the expansion of the universe. It's hard to see the universe collapsing under gravity when the expansion is accelerating. Short of bringing in very speculative theories about the end of the universe, the most likely prediction is for the distant future to be very cold, with all the stars burnt out, infinitely far apart from each other. This is the Big Freeze.



Meh. Imagine the distances in the universe being multiplied by a scale factor. Today the scale factor might be 1. In the past it was smaller. At the big bang it was 0. People don't seem to have much problem with the idea of an infinite universe coming from a singularity. It's a bit academic anyway, since our current laws of physics don't work at the big bang. Quantum and GR disagree. This doesn't usually matter, but it would near the big bang. We can only push our theories back as far as 10^-43 seconds after the bang. Until the two theories can be reconciled, people don't talk much about what happened before that.

And we don't know the universe to have a finite age. A lot of big problems in astrophysics can be solved by supposing that the universe spent an enormous amount of time lingering, prior to the sudden expansion 13.7bn years ago.

In other news, I've just finished my masters in astrophysics. Hazzah!

That what I was going to say

 

[Kangaroopit]

Agree with everything you say.

Particularly your first sentence, and this is, I guess, what I'm getting at. Biology has advanced in the last 500 years, by heaps! We now know a hell of a lot more, and our understanding is far more sophisticated. But, if we can keep ourselves from self-destructing through the end of the oil age and manage to continue to avoid global catastrophes, imagine what we'll know in another 500 years as our understanding of things such as quantum mechanics and multi-dimensional physics develops.

For instance: dark matter. We know stuff all about it, except that it's demonstrably there, and in massive volume. Could there be life of a type existing amongst it, feeding off it, equally invisible to us? It's well possible that there's things out there that our brains, developed over millenia to process just four of the multi-dimensions apparently out there, couldn't even physically conceive of.

It's a very interesting train of thought!

I'm going to go out on a limb here and say that there is no life in black holes. Anything in a black hole would be falling into the singularity very quickly. I'm guessing that even in a supermassive black hole, infalling objects would have a minute or less before they reached the singularity at the centre, when time would stop. A minute could hardly be expected to be enough time for life, or natural selection, to arise, especially when most of the infalling matter is just hydrogen gas, or the occasional rock. That's before coming to terms with other problems, like the strong gravitational forces that would stretch out any infalling object like spaghetti.

Another interesting detail is that nothing has fallen into a black hole yet. From our point of view, as outside observers, time slows down as you approach the surface of a black hole. At the surface itself, time slows to a halt. So everything that has ever fallen onto a black hole is still just above the surface, falling at an almost infinitesimal pace. Even given an infinite length of time, we would still be waiting, and still nothing would have fallen into a black hole.

Things are very different from the point of view of those unfortunate enough to fall in. They don't notice when they pass the surface, they find themselves going past it just fine, however, by the time they are past the surface, the entire history of the outside universe will have unfolded.

As for life made of dark matter... people would be very surprised. I think they're expecting dark matter to be quite simple particles, which the particle physicists wouldn't expect to be able to develop complex chemistries. They'll be trying to find out more about dark matter when they turn on the Large Hardron Collider at CERN next year.

 

[OzBomber]

Absolutely. The only life forms out there could be tiny amoeba floating around in a pond on some distant planet. Who knows. Then again, there could be advanced beings that make us look primitive. Scientists say that if the whole history of the universe was put into the scale of a clock, then humans have been around since 11:59pm.

So the universe is about to end!?!?

It just hurts thinking about it. How can the years keep going and going and never stop. How can space keep going and going and never stop.

 

[OzBomber]

The universe is apparently constantly expanding. Who knows what lies outside it though?

Maybe we could be in a little kid's world that he has made?

You do know, Humans can't be alive forever. We have to become extinct eventually. Just like the dinosaurs, I doubt that we'd be able to stay here forever. Eventually, conditions on earth will change, and it will probably be impossible to live on Earth. I've heard some stories that we're nearing another ice age.

Maybe the human race is smart enough to stay alive, but I don't know.

In terms of reaching an end... I'd be very confident in saying that wouldn't happen. If the universe isn't infinite, then we would expect it to be shaped as the surface of a 4-dimensional analogue of a sphere. This is difficult to visualise, but the point is that on the surface of a sphere, if you keep travelling, you get back to where you started. The same would be true of space. The universe would be finite but unbounded.

If you still go on this forum, and you can reply to this; so you're saying that if you keep travelling in the same direction, you'll end up in the same spot eventually?

 

[The Passenger]

Scientists say that if the whole history of the universe was put into the scale of a clock, then humans have been around since 11:59pm.

wouldn't we be at 12.01am as that's the start of the day??

 

[Jafa]

Absolutely. The only life forms out there could be tiny amoeba floating around in a pond on some distant planet. Who knows. Then again, there could be advanced beings that make us look primitive. Scientists say that if the whole history of the universe was put into the scale of a clock, then humans have been around since 11:59pm.

Pretty sure that analogy relates to the time scale since life began on earth.

 

[Kangaroopit]

If you still go on this forum, and you can reply to this; so you're saying that if you keep travelling in the same direction, you'll end up in the same spot eventually?

If the universe isn't infinite in extent, then yes. All the laws of geometry that you learn at school, like how the angles of a triangle add up to 180 degrees, aren't completely accurate in the real world. Anything with a mass distorts space and time slightly. This is much too small an effect to notice in every day life, but it has been confirmed by experiment. If the total mass of the universe is greater than a critical amount, then the total distortion caused to spacetime by all the mass would be enough to make the universe like a 3D equivalent of the 2D surface of a sphere. The surface of a sphere is 2D, but curved through a third dimension. The universe (if there is enough mass in it to make it this shape) would be 3D, and curved through a fourth dimension. This is obviously impossible to visualise, as we have no everyday experience of 4 dimensions, but the fact of curvature in a 4th dimension has been confirmed in many experiments.

So what would it mean for space to be a 3D analogue of the surface of a sphere? It would mean that, like travelling on the Earth, if you carry on travelling in the same direction for a long time, you would eventually get back to where you started. In practice, however, getting back to where you started would require you to travel faster than the speed of light, so it couldn't be done. In principle, however, if you could travel faster than light (which you can't) it would take you back to where you started.

Is the universe curved back on itself? Don't know. I said that the universe would have to weigh more than a certain amount for that to be so, and as far as we can tell, the mass of the universe is very very close to that amount. This could mean either that the universe is "flat" in the 4th dimension (which would mean that it's infinite in extent, like a flat sheet of paper going on forever), or that the universe is so big that it looks like it's flat. This would be like how the Earth might look like it's roughly flat where you are, but that's only because it's so big that you can't see the curvature.

Sorry if I haven't been clear there. Hope I was reasonably intelligable.

 

[OzBomber]

If the universe isn't infinite in extent, then yes. All the laws of geometry that you learn at school, like how the angles of a triangle add up to 180 degrees, aren't completely accurate in the real world. Anything with a mass distorts space and time slightly. This is much too small an effect to notice in every day life, but it has been confirmed by experiment. If the total mass of the universe is greater than a critical amount, then the total distortion caused to spacetime by all the mass would be enough to make the universe like a 3D equivalent of the 2D surface of a sphere. The surface of a sphere is 2D, but curved through a third dimension. The universe (if there is enough mass in it to make it this shape) would be 3D, and curved through a fourth dimension. This is obviously impossible to visualise, as we have no everyday experience of 4 dimensions, but the fact of curvature in a 4th dimension has been confirmed in many experiments.

So what would it mean for space to be a 3D analogue of the surface of a sphere? It would mean that, like travelling on the Earth, if you carry on travelling in the same direction for a long time, you would eventually get back to where you started. In practice, however, getting back to where you started would require you to travel faster than the speed of light, so it couldn't be done. In principle, however, if you could travel faster than light (which you can't) it would take you back to where you started.

Is the universe curved back on itself? Don't know. I said that the universe would have to weigh more than a certain amount for that to be so, and as far as we can tell, the mass of the universe is very very close to that amount. This could mean either that the universe is "flat" in the 4th dimension (which would mean that it's infinite in extent, like a flat sheet of paper going on forever), or that the universe is so big that it looks like it's flat. This would be like how the Earth might look like it's roughly flat where you are, but that's only because it's so big that you can't see the curvature.

Sorry if I haven't been clear there. Hope I was reasonably intelligable.

Reasonably intelligent? You're very intelligent!

On the 4D thing, what is a 4th dimension?

And why do you need to travel faster than the speed of light to get back to where you started?

 

[Leper]

may be the final fronteir, but it's made in a Hollywood basement.

 

[Kangaroopit]

Reasonably intelligent? You're very intelligent!

On the 4D thing, what is a 4th dimension?

And why do you need to travel faster than the speed of light to get back to where you started?

Intelligable, not intelligent, meaning understandable.

In our universe, there are three dimensions of space. Objects, simply put, all have a length, breadth and a depth. If you are telling someone exactly where something is, you would need three coordinates, which could be latitude, longitude and altitude. If the world were on a sheet of paper, it would be two dimensional. Objects could only have length and breadth, and to specify something's location, you would need only two numbers, which could be distance from the left margin and distance from the bottom. A perfectly thin line would have just one dimension, objects on it could only have a length and their locations could be identified with one number (their distance along the line). A point would have no dimensions.

If a 1D line were curved, it would still be 1D. If you imagine a river, and ignore its breadth and depth for a while, and imagine it as just having length, carrying 1D boats, then just because the river is curved wouldn't change the fact that you still only needed one number to tell someone how far up the river a boat would be. Likewise a piece of paper can be curved, and that won't make the objects on it 3D, even though we can see that the piece of paper is curved through a third dimesion: to specify where the paper is you need three numbers, but to specify where on the paper something is, you still only need two.

If people lived in a 2D universe, would they be able to tell that their universe was curved? Maybe. The universe can be curved in different sorts of ways. If the universe were on the surface of a sphere, then they could discover that their universe was curved by drawing a triangle. We're all taught at school that the internal angles of a triangle add up to 180 degrees, but that is only true if you draw the triangle on a flat surface. A triangle on the surface of a sphere would add up to more than 180 degrees. For example, if you started at the North Pole, and walked down to the equator, turned 90 degrees to your left, walked a quarter of the way around the Earth, turned 90 degrees left again and walked to the North pole, and finally turned 90 degrees left again so that you're facing your original direction, you would have made a triangle whose angles added up to 270 degrees. But you can only see the difference from 180 degrees if you walk around a very big triangle. A small triangle would be almost flat, and the angles would be close to 180 degrees.

If the residents of a 2D universe took three points, used their measuring tapes to draw the shortest possible lines between the points (which we would normally consider to be straight) and then measured the inside angles of the triangle and found that the angles added up to more than 180 degrees, they would know that their universe was on the surface of a sphere. But they would have to make a very large triangle before the difference from 180 showed up. They would then know that if they walked for a long time in any direction, amazingly and in spite of all their expectations, they would return to where they'd started.

Alternatively the universe could be curved like the surface of a saddle or a pringle. A triangle drawn on that shape would add up to less than 180 degrees. But this time, walking forever wouldn't take you back to where you started. If the pringle went on forever, you would never return to where you'd started. The universe would be infinite in extent. If the universe were either curved like a saddle/pringle, or like the surface of a sphere, we'd say that it had intrinsic curvature, in the jargon. Curvature is intrinsic if, when you tried to wrap a flat sheet of paper around the shape, you couldn't do so without tearing or folding the paper. The alternative is extrinsic curvature, which for example you'd get if you wrapped the paper around a cylinder, so that along one of its dimensions, you'd get back to where you'd started, but along the other, it would carry on forever, or until you reached the end of the paper. With extrinsic curvature, the angles of a triangle still add up to 180. They'd have to: if you draw a triangle on a piece of paper, the angles won't change just because you've wrapped the paper round a cylinder. Citizens of a universe shaped like the surface of a cylinder wouldn't be able to tell that their universe was curved unless they found that by walking for a long time in a certain direction, they got back to where they'd started.

So if we scale all this up, what would a 4th dimension be? We can't visualise it, because we have no experience of it, but we can tell it's there. For example, the mass of the Sun distorts space slightly, and means that Mercury follows a strange orbit that disobeys Newton's physics.

It seems obvious to everyone that the universe we live in should have three dimensions of space, because we can't visualise a 4th, but ultimately, what is so special about the number 3? Why three dimensions? The answer to this is that life as we know it could not exist in a universe with any other number. An animal in a 2D universe could not have a digestive system like ours, or it would be cut in two. In a 4D universe, atoms would be unstable. 3D is the only one where we could live.

Have a youtube video, by the late great Carl Sagan, about the 4th dimension:

[YOUTUBE]Y9KT4M7kiSw[/YOUTUBE]

The reason why you can't get back to where you started without travelling faster than light is that the universe is expanding, and the expansion is accelerating, so the distance you had still to go would always be increasing, unless perhaps if you could travel faster than light.

 

[Schism]

Life evolving on its own isn't the only way. Advanced races could easily seed planets, even galaxies. Hell, we are still primitive really, and even we could put life on other planets, or even terraform other planets if we got our shit together. Imagine what a race similar to us but 10,000 years more advanced and evolved could do. Transferring their soul or mind into immortal and near indestructable vessels would probably be the beginning.

 

[Niximus]

Out of interest, have you ever read any Stephen Baxter? If so, I'd love to hear your opinion as someone who actually knows what they are on about with these sorts of things. Personally, I think some of the concepts he writes about are amazing.

I have a lot of Stephen Baxter. My favourite is the one he co-wrote with Arthur C. Clarke - In The Light of Other Days - Great book.

 

[Smyth94]

I'm loving this thread, especially all the theories that are being thrown about - the best thing is, is that even the craziest person can have some shred of credibility.


Currently i'm reading through "Before the Fall-Out" by Diana Preston (development of the atomic bomb) and if there's one thing that stood out so far in this book is that theories that might seem crazy now may well be accepted as truth in a 100 years - the boundaries are almost limitless. Just a mere 100 years ago people thought Ernest Rutherford crazy for thinking that the atom could be split, or Einstein giving alternative views to the mechanical world of Newtonian physics.

 

[Ebert80]

So the universe is about to end!?!?

Isn't the sun due to blow up the universe in a hundred thousand years or so?

 

[Kangaroopit]

Isn't the sun due to blow up the universe in a hundred thousand years or so?

5 billion years till the Sun dies. But it's only about 2 billion before it gets too hot for animal life. Then plant life'll go a bit later. I think the oceans are boiling in 3.5bn years, from memory. We might be able to hold out a while longer if we have settlements on Mars or elsewhere by then.

The Sun will not take the universe with it. The Sun is a reasonably small star in a very, very big universe. There are about 1,000,000,000,000,000,000,000,000 stars in the small part of the universe that we can see, and some are dying all the time.

The mainstream answer for the end of the universe is that the universe will carry on expanding forever, all the stars will burn out, new stars will stop being formed because all their fuel will have been used up, eventually the universe will just get very cold and dark forever. Not the most inspiring prediction, but of course there might be other things we haven't discovered that would change that prediction.

 

[Kangaroopit]

That's what it'll look like, and I'm sure that nothing whatsoever could go wrong. Any takers? Just $US100,000 after the first 100 seats have gone. Some day... some day...


[YOUTUBE]WBo8t0B5NhM[/YOUTUBE]

 

[Dont be a lemon]

It shouldn't be too long until the survivors from the Twelve Colonies of Kobol find us

 

[Dan26]

Intelligable, not intelligent, meaning understandable.

In our universe, there are three dimensions of space. Objects, simply put, all have a length, breadth and a depth. If you are telling someone exactly where something is, you would need three coordinates, which could be latitude, longitude and altitude. If the world were on a sheet of paper, it would be two dimensional. Objects could only have length and breadth, and to specify something's location, you would need only two numbers, which could be distance from the left margin and distance from the bottom. A perfectly thin line would have just one dimension, objects on it could only have a length and their locations could be identified with one number (their distance along the line). A point would have no dimensions.

If a 1D line were curved, it would still be 1D. If you imagine a river, and ignore its breadth and depth for a while, and imagine it as just having length, carrying 1D boats, then just because the river is curved wouldn't change the fact that you still only needed one number to tell someone how far up the river a boat would be. Likewise a piece of paper can be curved, and that won't make the objects on it 3D, even though we can see that the piece of paper is curved through a third dimesion: to specify where the paper is you need three numbers, but to specify where on the paper something is, you still only need two.

If people lived in a 2D universe, would they be able to tell that their universe was curved? Maybe. The universe can be curved in different sorts of ways. If the universe were on the surface of a sphere, then they could discover that their universe was curved by drawing a triangle. We're all taught at school that the internal angles of a triangle add up to 180 degrees, but that is only true if you draw the triangle on a flat surface. A triangle on the surface of a sphere would add up to more than 180 degrees. For example, if you started at the North Pole, and walked down to the equator, turned 90 degrees to your left, walked a quarter of the way around the Earth, turned 90 degrees left again and walked to the North pole, and finally turned 90 degrees left again so that you're facing your original direction, you would have made a triangle whose angles added up to 270 degrees. But you can only see the difference from 180 degrees if you walk around a very big triangle. A small triangle would be almost flat, and the angles would be close to 180 degrees.

If the residents of a 2D universe took three points, used their measuring tapes to draw the shortest possible lines between the points (which we would normally consider to be straight) and then measured the inside angles of the triangle and found that the angles added up to more than 180 degrees, they would know that their universe was on the surface of a sphere. But they would have to make a very large triangle before the difference from 180 showed up. They would then know that if they walked for a long time in any direction, amazingly and in spite of all their expectations, they would return to where they'd started.

Alternatively the universe could be curved like the surface of a saddle or a pringle. A triangle drawn on that shape would add up to less than 180 degrees. But this time, walking forever wouldn't take you back to where you started. If the pringle went on forever, you would never return to where you'd started. The universe would be infinite in extent. If the universe were either curved like a saddle/pringle, or like the surface of a sphere, we'd say that it had intrinsic curvature, in the jargon. Curvature is intrinsic if, when you tried to wrap a flat sheet of paper around the shape, you couldn't do so without tearing or folding the paper. The alternative is extrinsic curvature, which for example you'd get if you wrapped the paper around a cylinder, so that along one of its dimensions, you'd get back to where you'd started, but along the other, it would carry on forever, or until you reached the end of the paper. With extrinsic curvature, the angles of a triangle still add up to 180. They'd have to: if you draw a triangle on a piece of paper, the angles won't change just because you've wrapped the paper round a cylinder. Citizens of a universe shaped like the surface of a cylinder wouldn't be able to tell that their universe was curved unless they found that by walking for a long time in a certain direction, they got back to where they'd started.

So if we scale all this up, what would a 4th dimension be? We can't visualise it, because we have no experience of it, but we can tell it's there. For example, the mass of the Sun distorts space slightly, and means that Mercury follows a strange orbit that disobeys Newton's physics.

It seems obvious to everyone that the universe we live in should have three dimensions of space, because we can't visualise a 4th, but ultimately, what is so special about the number 3? Why three dimensions? The answer to this is that life as we know it could not exist in a universe with any other number. An animal in a 2D universe could not have a digestive system like ours, or it would be cut in two. In a 4D universe, atoms would be unstable. 3D is the only one where we could live.

Have a youtube video, by the late great Carl Sagan, about the 4th dimension:

[YOUTUBE]Y9KT4M7kiSw[/YOUTUBE]

The reason why you can't get back to where you started without travelling faster than light is that the universe is expanding, and the expansion is accelerating, so the distance you had still to go would always be increasing, unless perhaps if you could travel faster than light.

I've heard it stated that the 5th dimension is probability. Meaning is the full amount of alternate realities that can happen. Or something like that anyway. Can you enlighten us on alternate realities? And their supposed existence.

 

[betterthanu]

Pretty sure that analogy relates to the time scale since life began on earth.

The universe timescale is in the scale of a calender. On that scale, humans have existed for the last second on December 31st. According to Carl Sagan on Cosmos anyway.

 

[Kangaroopit]

I've heard it stated that the 5th dimension is probability. Meaning is the full amount of alternate realities that can happen. Or something like that anyway. Can you enlighten us on alternate realities? And their supposed existence.

Wasn't the idea that the 5th dimension was something to do with probability from Mostly Harmless?

One thing that I deliberately didn't mention before is that the extra dimension in which space is curved is time. I thought that might confuse, and you don't really need to know that it is the case when you're trying to imagine curved space. Space and time aren't really seperate, but different aspects of the same thing.

As far as I know, there isn't a connection between parallel universes and extra dimensions. String theorists will claim that there are 10, 11 or 26 dimensions. I don't know how they reached those conclusions, but I do know that all the arguments for string theory are based on mathematical beauty. By all accounts string theory is startlingly elegant and beautiful, but that doesn't change the fact it is yet to produce a single experimental prediction, and that makes it quite contraversial. String theorists say that the extra dimensions are curled up in such a way that if you move even a very small amount in an extra direction you will return to where you started. It's like the universe being the surface of a hosepipe. If it's a thin hose, and you were looking at it from a distance, you might think it was just one dimensional, but actually there is a second dimension, you could go around the hose. String theorists think the universe is a bit like that, but with the extra dimensions being really tiny, so we don't see them.

Parallel universes seem to be brought up for two different reasons:

1. To explain the apparent fine tuning of the universe. There are physical constants that have to be set very specifically for the universe to be suitable for life. If you changed the strength of gravity, even to the fifteenth decimal place, then either the universe would have recollapsed after the Big Bang and formed a black hole or everything would have expanded forever and never formed stars and galaxies. Many people suggest that there are an infinite numer of universes, each with slightly different physical constants. It makes it seem less like luck that we are able to exist.

2. As a possible interpretation of quantum theory. It is claimed that there are myriad universes and that when something for which quantum effects are significant is measured, different universes will measure different things. That is an over-simplified and dulled down description of them, but they're worth reading about. I recommend The Fabric of Reality by David Deutsch. Though this interpretation is a minority viewpoint, it is a perfectly respectable one.