The edge of the Universe

[Bill32]

My dad is writing a sci-fi book. We constantly have disputes over his idea of "sci-fi". In his book, an outpost(humans) live on the last planet of their solar system. If the inhabitants look in one direction - they see stars and galaxies. But, if they look in the opposite direction - they see nothing !!! In another words this planet exists at the very edge of our universe !!! Looking in the opposite direction gives a person a view of space that does not, nor ever have contained stars, planets or galaxies !!!

How does my explaination of this planet, at the edge of the universe, conform to actual science, and what we know of the universe ??? That is, would it be possible to travel from Earth (in a sci-fi space craft)so far that you find yourself looking back at the stars ??? - and see no stars in front of you ??? (Sort of like when you drive away from a major city, and look back and see the city lights, then look forward and see nothing but the blackness of the desert !!&#33

Please respond. Thank you. :blink:

[GOURDHEAD]

The universe likely has no edge so what you postulate is like listening for the sound made by one hand clapping (not to be confused with Wan Hahn clapping). A reasonable metaphor is looking far an island at the edge of the surface of the earth.

A more likely case would be a planet in a stellar system on the outer edge of a galaxy which is itself at the exterior edge of a group of galaxies at the exterior edge of a super cluster of galaxies sufficiently far from the next supercluster such that the stars in the next supercluster are not detectable without the use of very sensitive instruments.

<_<

[Planetwatcher]

I aggree with GOURDHEAD.

Such a planet is possible, however it would not likely be within the life zone of the star. So artificial life support such as domes would have to be used. B)

[Haglund]

Why would it not be in the life zone of the star?

[Josh]

The edge of our solar system and the edge of the galaxy and the edge of the universe are VERY different things. I don&#39;t see why humans living at the last outpost in out solar system would mean they are at teh edge of the universe. Fair enough they won&#39;t see the inner planets but there are many other galaxies and comets to be seen when looking the other way.

And as to GOURDHEAD&#39;s comments...i say...Spot on. The universe is like an extra-dimensional planet in the respect you&#39;re talking about. An island at the edge of the planet - ie the surface- is exactly where you expect to find islands. In this case of the universe and the bodies within it there is not underground or sky analogy .. only the surface. So ... there is no edge of the universe&#33;

[imported_ROB]

[The universe likely has no edge so what you postulate is like listening for the sound made by one hand clapping (not to be confused with Wan Hahn clapping). A reasonable metaphor is looking far an island at the edge of the surface of the earth]

totaly agree
I cant remember where i read the link but its on the internet somewhere, It made a statment that said the universe was spherical as it expands so that if you set of from earth in one direction eventually you would arrive back at the same spot you started

[imported_ROB]

[QUOTE
I cant remember where i read the link but its on the internet somewhere]

found it it here

the universe

rob,

[Matthew]

You cannot get to the edge of the universe. It may have one, but you cannot reach it.

[Sp1ke]

Since the universe has been expanding since the big bang, you could say the edge is the outer limit of the expanding universe. Two problems with this: there&#39;s nothing beyond the edge since space-time only exists withing the universe, and the "edge" is expanding at the speed of light so there&#39;s no way to catch up with it nor to see anything when you&#39;re there.

[Haglund]

There&#39;s no real edge like the universe was a balloon or something, and it&#39;s likely that you will never reach the end of the universe, you would go in one direction forever, returning to the same position over and over again.

[Menikmati]

That is, would it be possible to travel from Earth (in a sci-fi space craft)so far that you find yourself looking back at the stars ???

If the universe was to be flat, then yes.

[Planetwatcher]

Why would it not be in the life zone of the star?

I wouldn&#39;t think of the edge of a solar system as being within the life zone, although I won&#39;t say it&#39;s impossible. But I was also thinking about the recent story of Voyager 1 encountering the helopause of our solar system.
Wouldn&#39;t it stand to reason that all stars have some kind of helopause? Which for the most part would define the edge of that star&#39;s solar system. And likely us as well if not for the Orrt Cloud.

Anyway, I wouldn&#39;t imagine a life zone planet could harbor life if it were in it&#39;s system helopause. Even if supported by artificial life support, it would seem to me that a helopause would cause some kind of disturbances in the planets natural order and or movement patterns. But I am presuming with no real evidence to back my presumptions. Just thinking with the keyboard.

[starrman]

In current cosmological understanding, it&#39;s a bit misleading to employ the term "edge" to concepts of the geometry of the universe. That said, one can consider that there is, in fact, an "informational edge" to the region of the universe which we earthbound observers can reach. At this time, best estimates for the age of the universe range in the area of 12 to 14 billion years. Thus, the most distant objects about which we can obtain information must reside within a spherical region centered on the earth with a radius of ~ 14 billion light years. Any objects more distant than that lie outside our "sphere of information," that part of the universe within which electromagnetic radiation - light, radio and microwaves, gamma radiation, etc. - has had time to arrive at our location. By definition, anything beyond that spherical volume of the universe cannot be known to us, and so might be said to lie "beyond the edge." Or at least beyond our local edge.

Clear skies.

[corkft]

For a good indication as to the true nature of the Universe, I would suggest reading the series "A Hitchhikers Guide to the Universe".

[Josh]

Heh ... not only will you find the answer to the true nature of the universe but possible answers to todays simple questions like "what is the meaning of life?"

[Tinaa]

I would quit arguing with your dad. You said it was a sci-fi book. He can make up his own rules in his universe. No one really knows if, when or where the edge is or isn&#39;t. Maybe the edge would look like a bubble from the inside.

[Haglund]

Originally posted by Planetwatcher@Nov 13 2003, 07:50 PM

Why would it not be in the life zone of the star?

I wouldn&#39;t think of the edge of a solar system as being within the life zone, although I won&#39;t say it&#39;s impossible.

Ok, if the planet is on the edge of its own solar system that would most likely be right.

But I was also thinking about the recent story of Voyager 1 encountering the helopause of our solar system.
Wouldn&#39;t it stand to reason that all stars have some kind of helopause? Which for the most part would define the edge of that star&#39;s solar system. And likely us as well if not for the Orrt Cloud.

Anyway, I wouldn&#39;t imagine a life zone planet could harbor life if it were in it&#39;s system helopause. Even if supported by artificial life support, it would seem to me that a helopause would cause some kind of disturbances in the planets natural order and or movement patterns. But I am presuming with no real evidence to back my presumptions. Just thinking with the keyboard.

No, of course not. Not life as we know it anyway... I&#39;m not sure that GOURDHEAD said that it would be at the edge of the solar system but only at the edge of its galaxy, and the galaxy being on the edge of its supercluster.

[Josh]

Bill32 sent me this email...

What about "farthest reaches"? That is, when the big bang occurred, the
universe expanded from that "point" outward. And, the universe is still
expanding. For hypothetical purposes, if I had a sci-fi star ship that could
get me to the "farthest reaches" of our known universe, i.e. get me to the "big
bang shock wave" or "wave front" - WHAT WOULD I OBSERVE? COULD I LOOK BACK ON
THE WAVE FRONT AND OBSERVE THE UNIVERSE, AND THEN LOOK FORWARD AND SEE
ABSOLUTELY NOTHING (because the universe has not expanded past this "front")?
If I had this hyper-speed ability, could I drive my star ship into the space in
front of the "big bang wave front"? Or, is this space not yet created, because
the "wave front" did not reach this area?

The answer, as far as we know the nature of the universe to date, is that you would look back and see the universe and look forward and still see the universe. The &#39;big bang&#39; was not an explosion with a point source that spread like we understand normal explosions of bombs etc. It was an explosion of space. not and explosion into space. This is also true given that the universe is likened to a computer game screen where things can go out of one side of the screen and in the other side. Like one of the so called "edges" (of which there are none) of the universe is linked to the other edges. If you travelled far enough in one direction you&#39;ve eventually come back to your starting point. Making any sense?

There are a number of other threads that this has been spoken about in. If you do a search for the phrase "big bang" in the search bar then you&#39;ll very likely hit upon the threads I&#39;m talking about. They&#39;re really quite interesting.

[Matthew]

Could it be 42? :P

[Planetwatcher]

No I don&#39;t suppose life as we know it could exist on a planet within a star&#39;s helopause. But then I wonder if even a planet could exist in such a location.

Who knows what kind of effects the tidal forces of a helopause may have on a planet&#39;s structure? Perhaps not unlike a moon inside the Roche limit of a planet.
Which is still speculated to have created the planetary rings of our gas giants.

As for a big bang wave front, If there was still a wave front created by the big bang, it would stand to reason that it would not be possible to put any kind of space ship in front of it, because there would be nothing in front of it.

Finally, I personally believe there are definitive boundries to our physical universe as we know it. However, those boundries are so far away that we either can&#39;t see them, the light images haven&#39;t yet reached us, or we don&#39;t know what to look for.

IMH Tinaa has hit the hammer square on the nail.

Maybe the edge would look like a bubble from the inside.

And if that were the case, the edge would likely be reflective in nature, perhaps even reflecting our own images back to us. And if it is doing just that it&#39;s entirely possible that we are in fact viewing multiple reflections of just a few images, much like having two mirrors facing each other, but from different angles, and different distances.

It may even be that there is only one, or perhaps very few galaxies in our universe, and all the rest we see are reflections of a much smaller universe then what we believe it to be.

However, don&#39;t call me a crackpot yet, because I didn&#39;t say &#39;this is for sure the way it is,&#39; but rather, &#39;this is a possibility of what may be, and happens to be what I personally believe&#39;. It surely warrents consideration.

[AusJosh]

Of course, you could always accelerate to Warp 10 and theoretically occupy every point in space at the same time (i would naturally assume this would include the edge)....

But then again, youd need to exist inside a science fiction series first....now theres the hard part.



-Josh

[StarQuestor]

So why NOT an EDGE?&#33;&#33;&#33;&#33;&#33; Nothing grates more against our intellectual skins than these concepts that can seemingly only be explained with brain exploding, mind numbing calculus or other forms of advanced math. From my own limited perspective it would seem that wether its space or matter expanding outward, that regardless of how counter intuitive it may be, regardless of how spherical our universe is where if you keep going in one direction, you have to eventually end up where you began, because I say for the universe to "expand", it has to expand INTO something&#33;&#33;&#33;&#33;&#33;&#33;&#33;&#33;& #33;&#33;&#33; Don&#39;t tell me that there is NOTHING it expands into&#33;&#33;&#33;&#33;&#33; I don&#39;t give a flaming, flying rats rear end about the circular nature of the universe&#33; I refuse to believe I live inside a megalithic video screen where we are permanantly locked inside a universe from which there is no escape when in the incredible countless trillion times a trillion years from now when there is no energy or matter left even to power a space ship that we can&#39;t somehow escape. If there is an edge, there has to be something OUTSIDE that edge...I don&#39;t think the universe is expanding inside of a concrete block. There must be some other muti or extra dimensional realm out there that all of this is expanding into. In other words, there has to be a place where an observer can look at it from the outside and watch it expanding. I realize this may be very naieve of me to think this way but you can dance around this metaphysical subject all you like with all the equations you can muster....if there is an edge, if it is expanding, then it by the very fact of its expansion must be expanding into something. Now its time for some serious open speculation on what the "something" is that the universe is expanding into. What exists outside the expanding universe? Come on people, lets not run from this subject simply because we have no way of finding out until we are dead&#33;

[Sp1ke]

I think Josh&#39;s answer earlier shows why there doesn&#39;t have to be an edge. The universe&#39;s expansion is the expansion of space so there&#39;s nothing else. If "space" is what you call "everything", then this is what is expanding so there&#39;s nothing outside it so it hasn&#39;t got an edge.

Since the universe is expanding at the speed of light, there is no way to travel faster than it so it is impossible to get "outside" the universe.

It&#39;s not that the universe is expanding into a vacuum - even a vacuum is part of space.

The reason any discussion becomes counterintuitive or "brain-exploding" is that it&#39;s difficult to think about something that we can never perceive or participate in. If there isn&#39;t an edge, there is no way for a human to stand outside the universe and watch it expand. What does a four-dimensional cube look like? What about a 6-dimensional cube? 20-dimensional? There aren&#39;t any simple answers. Just saying there "has to be an edge" doesn&#39;t make it so. It&#39;s not that simple - but it&#39;s still worth persisting in trying to get your head round the concept.

What about thinking of it in two dimensions? If you imagine we&#39;re two-dimensional beings, living on a three-dimensional world. We can travel any distance on the surface without reaching an edge. If you travel far enough in one direction, you get back to where you started. If you then imagine the world is expanding at the speed of light, you can never travel fast enough to go round the world as it&#39;s growing as quick or quicker than you can move. What you can&#39;t do, as a two-dimensional being, is to leave the surface and travel in the extra dimension to get "above" the world to see it expanding.

[Planetwatcher]

But everything has an end, and beginning.

[Sp1ke]

A circle doesn&#39;t

[StarQuestor]

An excellent reply to my tirad Sp1ke. The analogy to the two dimensional existance from a 3D point of view is very good. There are a couple holes but its still very good. From our 3D point of view, we can see the surface of a 2D surface...expanding or otherwise. If expanding, then it is obviously expanding into our 3D universe. So then, what universe or dimension is our universe expanding into.

[damienpaul]

a sphere doesn&#39;t either

[StarQuestor]

Gentlemen, your argument is as circular as your answers&#33;....Its a cop out. Come on, you can do better. Sphere, circle, marble or whatever only avoids the real question....what lies beyond? I imply the universe exists wether spherically or otherwise is to imply it exits inside something else. No other logic can exist in this matter...but I welcome any speculation. That is, after all, what all this is about...LOL.

[Sp1ke]

Well... it all depends on what you mean by "beyond" the universe.

If the universe is the realm of our space and time, there is no space and time (as we define it) outside our universe. This might be where the expanding sphere analogy breaks down. Bear with me and I&#39;ll see if I can get my head round it.

If you&#39;re two-dimensional and on an expanding three-dimensional sphere, the sphere is expanding into the third dimension. So the three-D universe could be expanding into a fourth spatial dimension (forgetting about time as a fourth dimension for now). So that determines the direction of expansion. But it doesn&#39;t address what&#39;s actually outside the universe.

I guess you could say that in a hyper-universe of four spatial dimensions and one time dimension, what&#39;s outside our 3-D universe could be other universes, empty space, a sea of energy. Basically anything. But completely unobservable by us since we can never reach the edge of our universe.

[Josh]

This was emailed to me by Professor Paul Davies in order to shed some light onto the question about whether there is an edge to the universe. Paul Davies is a physicist and cosmologist at The Australian Centre for Astrobiology, Macquarie University, Sydney. His latest book is How to Build a Time Machine. The above essay is based on his book The Edge of Infinity. Everyone here at Universe Today would like to thank Professor Davies for his time and answer&#33;
__________________________________________________ ____

Where is the centre of the universe?

Because other galaxies are rushing away from us, it might seems as if Earth must lie close to the centre of the universe. This is completely wrong. The pattern of expansion Hubble discovered has the special form that every cluster of galaxies moves away from every other cluster. Whichever cluster you were situated on, the pattern of motion around you would look the same. An analogy might help. Suppose by some magic our planet were to expand noticeably every day. The distance between cities would then steadily increase. Manchester would move away from London, New York would move away from Chicago and Beijing would move away from Hong Kong. Pick any two cities, and the distance between them would increase. Viewed from any particular city, all the others would seem to be retreating. But in fact no city is special. None lies at the centre of the pattern. Notice also that if the Earth expanded uniformly (rather than fast here and slow there), then a city twice as far away would retreat twice as fast: Manchester would move away from London roughly twice as fast as Birmingham. This is precisely the pattern that Hubble observed: galaxies twice as far away retreat at twice the speed. Hence we can conclude that the universe is expanding at the same rate everywhere, and no galaxy lies at the centre of the expansion.

But mustn’t there be a centre somewhere, even if we can’t spot it?

Well… It’s perfectly logical to have a truly infinite expanding universe, the same everywhere on average. Then there would be no centre and no edge at all. However, this would be indistinguishable from a universe that is merely stupendously big, with us located well away from the edge.

If it is just very big but finite, couldn’t we build a super-duper telescope and see the edge?

There is a snag with this strategy. A telescope is also a time-scope. An astronomer looking at a galaxy, say, five billion light years away sees the galaxy as it was five billion years ago, not as it is now. That’s because light travels at a finite speed (one light year per year). Physicists are convinced that the speed of light is a cosmic speed limit – nothing can go faster. So no matter how fancy our instruments, there is a limit to how far we can peer into space. This limit is set by the age of the universe. If it’s 13.7 billion years old, we can’t detect anything more than 13.7 billion light years away. So we are left wondering whether the patch of universe we see is typical of the whole – and it just goes on for ever and ever in every direction looking much the same – or whether, sooner or later, it would come to an end – or an edge – and change into something else. And if so, what? That is the basis of the recent popular “multiverse” idea: that there is an edge out there somewhere, but probably a very very long way away. From what I have written, it’s clear we will not discover the multiverse by peering yet deeper into space. Evidence for it rests on other arguments.

Why do newspapers often talk about astronomers seeing to the edge of the universe?

This is just sloppy talk. “The edge of the universe” can sometimes refer to the limit of visibility using current instruments – so not a physical edge in any sense. Or it can refer to factor I have just mentioned – the limit imposed by the finite speed of light. This isn’t an abrupt cut off. What happens is this. The farther into space astronomers look, the redder the galaxies become. At about 13 billion light years the universe is too young for proper galaxies with stars. This is the so-called cosmic Dark Age. Before that is just glowing gas, spread evenly through space, and seen by us as hugely red-shifted to a temperature of only 2.7 degrees above absolute zero. This “wall of light” lies about 380,000 light years from the “edge” defined as the limit due to the finite speed of light. This “light” edge is known technically as our particle horizon. It no more represents a true edge of the universe than a horizon on Earth represents an edge to the planet. Rather, the horizon is merely a fundamental limit of visibility. The particle horizon increases in radius with time, by one light year per year.

The above discussion is predicated on the assumption that the big bang was a true origin of time, so that nothing can reach us from the epoch before it (because, by definition, there was no “before”). That is the case with the normal, orthodox cosmological model. However, more recent models, based on eternal inflation and predicting a multiverse, treat the big bang as a local, not a global origin. In these more elaborate models, our particle horizon is no longer a true causal boundary, but it remains an observational boundary, since the big bang completely reconfigured spacetime, and reprocessed matter and energy so thoroughly that it would not be possible to look back through it to a preceding cosmic epoch. Largely this is because inflation, by its very nature, erases all information about prior epochs. So the distinction between the orthodox big bang and the more elaborate inflation/multiverse models is essentially a conceptual rather than an observational one.

Paul Davies