Does the universe have an edge?

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Offline Alan McDougall

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Does the universe have an edge?
« on: 31/05/2016 05:59:39 »

Does the universe have an edge?


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- See more at:     http://www.space.com/33005-where-is-the-universes-edge-op-ed.html?cmpid=NL_SP_weekly_2016-5-30#sthash.w63MWnXv.dpuf

Let's take a step back. Everyone knows those common analogies used to describe an expanding universe: Galaxies are like ants crawling around on a beach ball. We're all raisins in a loaf of bread. And oh! the beach ball is inflating! Yes! The loaf of bread is rising in the oven! Space is expanding, and the galaxies are carried along with it! See? Easy!

Those analogies certainly get across an important point: The galaxies aren't flying or shooting or waltzing away from each other. It's the space underneath them that's doing all the work of expanding; the galaxies are just along for the cosmic carpet ride.

But those analogies also carry a fatal flaw. We can all easily imagine an inflating beach ball or a rising loaf of bread, and we immediately think of them as expanding into something: empty air. The beach ball has a skin. The loaf has a delicious, crunchy crust. They have edges, and they're moving into something.

Our minds have played a trick on us, and it's cheating us from being fully awestruck at what's going on.

But our real universe is three-dimensional. While string theory suggests there might be extra dimensions, they're all supertiny, so those don't count. So is there a fourth extra dimension that provides the "stuff" for our universe to expand into?

Maybe, maybe not. Here's the thing: The mathematics could support a fourth dimension for our 3D universe to expand into. And we would definitely have an "edge" in this extra dimension, the same way you can point to the "edge" of a 2D beach ball surface.

The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #1 on: 31/05/2016 08:19:48 »
Nobody knows for sure whether the universe has an edge.

But for myself, I object to the non-sequitur that has arisen since WMAP evidence indicated that the universe is flat. This says "the universe is flat so it must be infinite". It just doesn't follow, I object to this unscientific unjustified claim. I also object to the way "when the universe was the size of a grapefruit" has now morphed to "when the observable universe was the size of a grapefruit".

I have no issues with big bang cosmology, or the expanding universe. But I do have issues with what comes across the as the flip side of flat Earth cosmology. In olden days it is said that some people could not conceive of a world without an edge. In modern times it seems that some people cannot conceive of a world with an edge.

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Offline impyre

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Re: Does the universe have an edge?
« Reply #2 on: 31/05/2016 09:46:07 »
I just think it's hard to imagine the type of edge that a universe could have, so it seems easier to accept that it has none. Maybe it's counter-intuitive, but it's pretty straightforward to imagine being able to go in any given direction for an indeterminate amount of time until all the galaxies recede into the distance and you're simply left with empty space. Like if you walk from the center of town outward long enough, signs of people start to become less frequent until you're off in the woods somewhere alone.

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Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #3 on: 31/05/2016 12:00:26 »
I just think it's hard to imagine the type of edge that a universe could have, so it seems easier to accept that it has none. Maybe it's counter-intuitive, but it's pretty straightforward to imagine being able to go in any given direction for an indeterminate amount of time until all the galaxies recede into the distance and you're simply left with empty space. Like if you walk from the center of town outward long enough, signs of people start to become less frequent until you're off in the woods somewhere alone.

A warm welcome to our forum!

What about the "Universe is Everything Expanding"
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #4 on: 31/05/2016 13:59:41 »
I just think it's hard to imagine the type of edge that a universe could have, so it seems easier to accept that it has none...
I think it's pretty easy to imagine waves in a water droplet. When they reach the edge of the water they don't keep on going, because there's no water past the edge of the water. Instead they undergo total internal reflection. Then IMHO you can apply this to waves in space rather than waves in water. When they reach the edge of space they don't keep on going, because there's no space past the edge of space. Instead they undergo total internal reflection. There's something akin to this general idea in this old article featuring Neil Cornish. It refers to a "hall of mirrors" universe:

"The focus of the new work, which was published last week in the journal Physical Review Letters, was a search of background radiation data for paired circles that would have indicated the universe is like a hall of mirrors, in which multiple images of the same object could show up in different locations in space-time. A hall of mirrors could mean the universe is finite but tricks us into thinking it is infinite..."

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Offline impyre

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Re: Does the universe have an edge?
« Reply #5 on: 01/06/2016 12:44:45 »
Thanks for the welcome. I wasn't suggesting that I couldn't imagine an edge, I was just offering a reason why people might shy away from the idea. Your analogy is an excellent example of what most people might try to use to make sense of the idea of an edge to the universe. However, it conjures images of reflection and a hard stoppage... which makes people think of giant walls around the universe. This probably "feels" wrong, just like the idea of the "edge of the world" feels wrong to many people nowadays. No way to know for sure what's there. I'm partial to the no-edge idea myself. That's what I think because it "feels" right to me, but I wouldn't put any money on it lol.

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Offline impyre

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Re: Does the universe have an edge?
« Reply #6 on: 01/06/2016 13:03:09 »
What about the "Universe is Everything Expanding"
I don't think that has any bearing on the question of whether the universe has an edge. It can expand whether there's an edge or not.

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #7 on: 01/06/2016 13:04:50 »
It's good to talk, impyre. I dislike the infinite-universe idea because I just can't see how an infinite universe can expand. It seems to be totally at odds with big bang cosmology to me. 

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #8 on: 01/06/2016 13:32:50 »
That's because you don't know what you are talking about John.
Fixation on the Einstein papers is a good definition of OCD.

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Offline acsinuk

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Re: Does the universe have an edge?
« Reply #9 on: 01/06/2016 13:37:51 »
The universe must have an edge because there is a limit to the red shift.  The inner universe is magnetised but beyond the edge it is not magnetised so it cannot exist.
A.C.Stevens

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Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #10 on: 01/06/2016 14:47:25 »
It's good to talk, impyre. I dislike the infinite-universe idea because I just can't see how an infinite universe can expand. It seems to be totally at odds with big bang cosmology to me. 

Don't worry John was you say makes sense to me our universe is finite it had a beginning and it will have an end, because it cannot escape the terrible grip of increasing entropy!
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline impyre

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Re: Does the universe have an edge?
« Reply #11 on: 01/06/2016 15:41:44 »
It's good to talk, impyre. I dislike the infinite-universe idea because I just can't see how an infinite universe can expand. It seems to be totally at odds with big bang cosmology to me. 
Yes, talking is good. As to how an infinite universe can expand, we do this all the time in math (and even visually). Consider an infinite number-line like the x-axis. It goes on infinitely in either direction. If we then consider changing it to something else, we can call it the g-axis, the new axis might not map directly to the old. If for each g = 10x, then we've expanded the entire axis. This can happen instantly if you like, or gradually (think like "zooming in" or "magnifying"). Something that was at .2 on the old system is now at 2 on the new system; likewise, something at 2 on the old system is at 20 on the new system. Furthermore, the distance between where .2 and 2 used to be is also now magnified as well. It used to be 1.8, and is now 18 (the distance between 2 and 20). So we can see that with this transformation it isn't simply points being shifted, it's the actual axis being stretched... and even "empty" spaces are stretched as well.
This type of transformation can occur in two dimensions also, or any arbitrary number of dimensions. The only requirement is that the transformation (expansion in this case) affects the entire space in the same way, not necessarily that it be finite.

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Offline Thebox

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Re: Does the universe have an edge?
« Reply #12 on: 01/06/2016 16:03:31 »
It's good to talk, impyre. I dislike the infinite-universe idea because I just can't see how an infinite universe can expand. It seems to be totally at odds with big bang cosmology to me.

Good day sir, infinite is a kind of misleading word, on a recent forum I learnt the term unbounded and bounded, I much prefer these terms than an infinite Universe. Present information suggest an expanding space, however this could be quite well conceivably ''wrong'', space is made of ''nothing'' but is not nothing, it is space. However it would be rather '''wrong'' of us to perceive that ''nothing'' can expand or that beyond visual space there is absolutely nothing, light travels in any direction from a ''spherical'' output,  what we observe is distant galaxies, we perceive these are about 14.6 billion light years away, if that is a 'true' measurement, then we must also perceive that at the far side of the distant galaxies the light also travels at least 14.6 billion light years away making a total of 29.2 billion light years of distance.
Some overlooked facts are that a 3 dimensional object that moves away from you will become a visual 2d object, the more and more the object travels away from you , the greater the visual area contraction is, the visual angle of light collapsing to a 0 dimension singularity ''whole''.   People of the world fail to ''see'' beyond the ''firmament'' of the ''edge'' of space, the ''edge'' being relative to visual area contraction and the intensity of light over a distance. What you observe when you look into the night sky and are not directly observing a point source, (the relative blackness ''edge''), is actually clear and a clarity.
So ''see' that the edge of space is not really an edge. it is the limitation of light and relative ''area'' of an object.
Now what you may find interesting, is that in the dark is the same as looking into space, only light ''reflecting'' or light emitting ''matter'' can be seen. The distance remains the same in the dark, and if all the distant galaxies were to suddenly ''vanish'', the ''size' of the Universe would visually  contract to the ''size'' of the milky way, the ''edge'' contracting , in extending this further, without ''light'' space becomes an unknown , space would contract to the ''size'' of your brain.
Measurement of a distance/length only exists between two point sources, relatively if ''you'' were the only point source in the Universe, you would ''see'' no distance/length.



« Last Edit: 01/06/2016 16:17:10 by Thebox »

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Offline Thebox

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Re: Does the universe have an edge?
« Reply #13 on: 01/06/2016 16:07:26 »
It's good to talk, impyre. I dislike the infinite-universe idea because I just can't see how an infinite universe can expand. It seems to be totally at odds with big bang cosmology to me. 
Yes, talking is good. As to how an infinite universe can expand, we do this all the time in math (and even visually). Consider an infinite number-line like the x-axis. It goes on infinitely in either direction. If we then consider changing it to something else, we can call it the g-axis, the new axis might not map directly to the old. If for each g = 10x, then we've expanded the entire axis. This can happen instantly if you like, or gradually (think like "zooming in" or "magnifying"). Something that was at .2 on the old system is now at 2 on the new system; likewise, something at 2 on the old system is at 20 on the new system. Furthermore, the distance between where .2 and 2 used to be is also now magnified as well. It used to be 1.8, and is now 18 (the distance between 2 and 20). So we can see that with this transformation it isn't simply points being shifted, it's the actual axis being stretched... and even "empty" spaces are stretched as well.
This type of transformation can occur in two dimensions also, or any arbitrary number of dimensions. The only requirement is that the transformation (expansion in this case) affects the entire space in the same way, not necessarily that it be finite.

[tex]\rightharpoon\atop{an∞}[/tex]

Added - sorry the forum maths tool did not like my change.

[tex]\rightharpoon\atop{a0}[/tex]
« Last Edit: 01/06/2016 16:10:04 by Thebox »

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Offline impyre

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Re: Does the universe have an edge?
« Reply #14 on: 01/06/2016 16:16:19 »
I'm not sure what the a0 vector symbol means or is for.

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Offline Thebox

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Re: Does the universe have an edge?
« Reply #15 on: 01/06/2016 16:21:49 »
I'm not sure what the a0 vector symbol means or is for.

Imagine you are (a) at point 0 looking into space where there is no point sources, i.e the edge, that is why the second ''point'' of the vector is zero, there is nothing there to ''see'' , or simply close your eyes or turn the light out.


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Offline impyre

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Re: Does the universe have an edge?
« Reply #16 on: 01/06/2016 16:39:54 »
Thanks for clarifying your post. I just don't think it's that simple. If you're describing an edge or end, then you must describe what we might call "end behavior". In the water drop example, even this isn't as straightforward as you might at first think. Sure, if you're simply a vibration in the water then the edge of the drop may as well be a solid wall you bounce off due to surface tension and how waves behave at the fluid interface... but even that's not the end of that because a compression wave with enough amplitude or velocity might actually break through from the inside causing a burst of water to shoot out. So if you're a vibration in a water droplet, the edge is semi-hard. If you're something with more... substance, like a pebble... then it really poses no obstacle at all.

But for something like the edge of the universe the possibilities are as boundless as our imagination really. Perhaps it's total blackness without form or solidity... you can pass right off the edge of the universe, but anything that passes the edge ceases to exist. You'd never get your hand back. Or maybe it will feel more solid. Since there's technically no space-time fabric left then motion cannot occur at all past the edge... this would suggest a hard surface that physically stops all motion... you could crash into it. Light would just freeze at the edge. My point is that no matter how you describe it, the idea of an edge creates strange behaviors.

If what you're describing is something that isn't a physical edge, just a place where there are no more stars... well I've already described that as an infinite universe with a finite population of matter. Let's not forget that there may be multiple dimensions, and what looks infinite in three dimensions may well be finite in 4 or 5. Space could be contorted in such a way as to appear flat and infinite in 3 dimensions, and in reality be quite limited in size.

Another possibility is that the edge  occurs bounding the universe in a finite volume, but spacetime expands the closer you get to the edge... you could travel forever and never find any apparent edge. Who knows, but edges still seem odd to me... I keep thinking of that episode of futurama. :p

Edit: Also I feel it important to clarify that what I'm attempting to describe is any theoretical edge of the universe if it were to exist independent of observation. I feel that's important because it's a key factor in reproducibility... which is to say that if something is true and is to be considered a fact, it should always be true. If a model has exceptions, they should be enumerated such that the model gives predictability. I'm talking more about physical reality, at least as far as we can measure and perceive it.

edit2: needed paragraphs
« Last Edit: 01/06/2016 16:49:03 by impyre »

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Offline Thebox

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Re: Does the universe have an edge?
« Reply #17 on: 01/06/2016 16:58:47 »
Thanks for clarifying your post. I just don't think it's that simple.

It really is that simple and quite easily provable by using present information and simple experiments.





Quote
If you're describing an edge or end, then you must describe what we might call "end behavior".

Well the end behaviour is simple, it is a limitation to the ''size'' of an object, there is an eventuality that any ''matter'' travelling away from an observer will visually contract to 0 dimensions and 0 visual angle  of light unless the ''matter'' was ''infinite'' in size.


Quote
But for something like the edge of the universe the possibilities are as boundless as our imagination really. Perhaps it's total blackness without form or solidity... you can pass right off the edge of the universe,

You can pass right of the ''edge'' of the visual boundary of the Universe and visually contract from the line of sight. 





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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #18 on: 01/06/2016 17:12:32 »
Yes, talking is good. As to how an infinite universe can expand, we do this all the time in math (and even visually). Consider an infinite number-line like the x-axis. It goes on infinitely in either direction. If we then consider changing it to something else, we can call it the g-axis, the new axis might not map directly to the old...
I'm sorry impyre, but this mathematical infinity doesn't "work" in terms of the physics. If you take a look at the stress-energy-momentum tensor, you can see an energy-pressure diagonal:


Public domain image by Maschen, based on File:StressEnergyTensor.svg created by Bamse


The stress-energy-momentum tensor "describes the density and flux of energy and momentum in spacetime". IMHO you can think of space as having a kind of "pressure" to it, that causes it to expand. But in an infinite universe, this pressure is counterbalanced at all locations, so space can't expand. 


So if you're a vibration in a water droplet, the edge is semi-hard. If you're something with more... substance, like a pebble... then it really poses no obstacle at all.
Don't forget the wave nature of matter!

« Last Edit: 01/06/2016 17:20:34 by JohnDuffield »

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #19 on: 01/06/2016 17:18:32 »
Good day sir, infinite is a kind of misleading word, on a recent forum I learnt the term unbounded and bounded, I much prefer these terms than an infinite Universe. Present information suggest an expanding space, however this could be quite well conceivably ''wrong'', space is made of ''nothing'' but is not nothing, it is space...
Agreed. Oddly enough, when you read the Einstein digital papers, space comes across as a kind of gin-clear ghostly elastic thing that you can curve and stress et cetera. See the post above, where I inserted a picture of the stress-energy-momentum tensor? On the right you can see a shear stress term. That's the sort of thing you see in continuum mechanics.   

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Offline impyre

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Re: Does the universe have an edge?
« Reply #20 on: 01/06/2016 17:34:03 »
Well, it seems to me that the stress-energy tensor is used to solve for forces and momenta in relativistic space. I don't know about any space pressure or how that would be responsible for expanding space-time. As far as observations show, space-time is expanding in as many dimensions as we can measure. This expansion can happen just as readily in an infinite universe as in a finite one... just as space-time can be relativistic without making any implication about its topology in multiple dimensions.

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Offline Thebox

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Re: Does the universe have an edge?
« Reply #21 on: 01/06/2016 17:55:20 »
Good day sir, infinite is a kind of misleading word, on a recent forum I learnt the term unbounded and bounded, I much prefer these terms than an infinite Universe. Present information suggest an expanding space, however this could be quite well conceivably ''wrong'', space is made of ''nothing'' but is not nothing, it is space...
Agreed. Oddly enough, when you read the Einstein digital papers, space comes across as a kind of gin-clear ghostly elastic thing that you can curve and stress et cetera. See the post above, where I inserted a picture of the stress-energy-momentum tensor? On the right you can see a shear stress term. That's the sort of thing you see in continuum mechanics.

Thank you Sir for the very interesting link to a person whom I admire in respect to his thinking. I feel I understand Albert but also feel that the curvatures in his imagination are more of ''things'' that occupy space rather than space. It is apparent to me that the gin-clear space is the gin-clear of ''light'' passing through space. We observe when space is occupied by light the clarity that is not opaque to sight as opposed to ''darkness'' which is relatively ''opaque'' whether it be of the mind or of space.
We as the observers could not relatively ''see'' any possible curvature of ''light'' or forces in space because the space is ''see through'' and all things passing through or occupying space that is not of concrete existence is ''invisible'' to observation.
So in reply to your post, what of space are you defining is stressed ? No aether exists and space is not of solidity.

 

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #22 on: 01/06/2016 19:50:42 »
Good day sir, infinite is a kind of misleading word, on a recent forum I learnt the term unbounded and bounded, I much prefer these terms than an infinite Universe. Present information suggest an expanding space, however this could be quite well conceivably ''wrong'', space is made of ''nothing'' but is not nothing, it is space...
Agreed. Oddly enough, when you read the Einstein digital papers, space comes across as a kind of gin-clear ghostly elastic thing that you can curve and stress et cetera. See the post above, where I inserted a picture of the stress-energy-momentum tensor? On the right you can see a shear stress term. That's the sort of thing you see in continuum mechanics.

So John you are seriously saying you understand continuum mechanics? Go on then tell me what it is all about. In a nutshell so to speak. You may even impress me.
Fixation on the Einstein papers is a good definition of OCD.

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #23 on: 01/06/2016 19:57:11 »
You'll have to bear with me I'm just getting a coffee and will be settling into a comfy chair to wait.
Fixation on the Einstein papers is a good definition of OCD.

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #24 on: 01/06/2016 21:21:42 »
Well, it seems to me that the stress-UK energy tensor is used to solve for forces and momenta in relativistic space. I don't know about any space pressure or how that would be responsible for expanding space-time. As far as observations show, space-time is expanding in as many dimensions as we can measure. This expansion can happen just as readily in an infinite universe as in a finite one... just as space-time can be relativistic without making any implication about its topology in multiple dimensions.

Anything John says should be taken with a pinch of salt.
Fixation on the Einstein papers is a good definition of OCD.

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Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #25 on: 02/06/2016 07:56:35 »
Quote from: Alan McDougall

Does the universe have an edge?

No. At least not according to current theory. Please don't confuse what is mathematically possible with what is physically "true."

The comments in your quote are quite misleading. To be exact, the comment But those analogies also carry a fatal flaw. is quite wrong. When the analogy is used it is made clear that there is no dimensions off the surface of the balloon, that the universe is not expanding into a higher dimension. That's part of using the analogy, i.e. explaining exactly what the analogy entails.

Quote from: acsinuk
The universe must have an edge because there is a limit to the red shift.
The limit to redshift is due to galaxies lying outside the Hubble sphere which means that they're traveling faster than the speed of light as measured by observers at our location. All of that simply means that the only reason why there is a limit to cosmological redshift is because those galaxies are so far away that they lie outside the Hubble sphere and for that reason we can't see them. However, different observers have a different Hubble sphere which means that those galaxies that we can't see can be seen by other observers and therefore there is a corresponding redshift associated with them.

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Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #26 on: 02/06/2016 08:27:36 »
Quote from: Alan McDougall

Does the universe have an edge?

No. At least not according to current theory. Please don't confuse what is mathematically possible with what is physically "true."

The comments in your quote are quite misleading. To be exact, the comment But those analogies also carry a fatal flaw. is quite wrong. When the analogy is used it is made clear that there is no dimensions off the surface of the balloon, that the universe is not expanding into a higher dimension. That's part of using the analogy, i.e. explaining exactly what the analogy entails.

Quote from: acsinuk
The universe must have an edge because there is a limit to the red shift.
The limit to redshift is due to galaxies lying outside the Hubble sphere which means that they're traveling faster than the speed of light as measured by observers at our location. All of that simply means that the only reason why there is a limit to cosmological redshift is because those galaxies are so far away that they lie outside the Hubble sphere and for that reason we can't see them. However, different observers have a different Hubble sphere which means that those galaxies that we can't see can be seen by other observers and therefore there is a corresponding redshift associated with them.

OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline impyre

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Re: Does the universe have an edge?
« Reply #27 on: 02/06/2016 12:12:55 »
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
Actually, I agree with him. In his defense he did say "according to theory", which is a pretty accurate statement as far as I know. Further, he might been better off saying that the comment was over-reaching in its implication rather than flat-out wrong, but again I agree with him. Almost any analogy can work in-so-far as its intended breadth and depth; however, any analogy can be extended beyond the original intent of the person who made the analogy, and in this extension become false or outright ridiculous. This is a common structure for an argument similar to reductio ad absurdum arguments. "Well if electricity works like water... I should be able to swim in it... but I can't, so therefore this analogy is flawed." This is a classic example of an analogy simply being taken much too far. The most basic principles of electricity do very much resemble water as all the basic components are there. Pressure to voltage, current to rate of flow, resistance to resistance, etc... but even this analogy breaks down past a certain point.

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #28 on: 02/06/2016 14:37:40 »
Thank you Sir for the very interesting link to a person whom I admire in respect to his thinking. I feel I understand Albert but also feel that the curvatures in his imagination are more of ''things'' that occupy space rather than space.
It's actually a curved "metric". We call it curved spacetime, but curved spacetime isn't curved space and time, it's a curvature in your plot of measurements of distance and time . For example you place a whole lot of optical clocks at different elevations. The lower clocks go slower, and when you plot all the clock rates, there's a curve in your graph.

We as the observers could not relatively ''see'' any possible curvature of ''light''
We do. We see gravitational lensing.

So in reply to your post, what of space are you defining is stressed?
The space around the Earth. The stress-energy- momentum tensor is called what it is for a reason. It "describes the density and flux of energy and momentum in spacetime". Stress is directional pressure. In simple terms, a gravitational field is a spatial pressure gradient.

No aether exists and space is not of solidity.
You should read Einstein's Leyden Address where he described space as the aether of general relativity. Here it is:



General relativity really does treat space like a gin-clear ghostly elastic solid. Google on Einstein elastic.

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #29 on: 02/06/2016 14:55:26 »
Actually, I agree with him. In his defense he did say "according to theory", which is a pretty accurate statement as far as I know.
The trouble with this is that the theory is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". This assumption says wherever you are, space will look the same in all directions. But it isn't scientific. For all we know, some guy 46 billion light years away sees one half of the night sky as completely black. Or as a mirror image of the other. Or something else. We just don't know.
 
Almost any analogy can work in-so-far as its intended breadth and depth...
One analogy used to explain an edge-less expanding universe is the balloon analogy. I don't like it because we have no evidence of any higher dimensions, and no evidence of any kind of curvature that would cause you to go round in great big circles. Hence I prefer the raisin-cake analogy. And I note that a raisin cake has  an edge. 

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Offline Thebox

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Re: Does the universe have an edge?
« Reply #30 on: 02/06/2016 17:20:57 »
It's actually a curved "metric". We call it curved spacetime, but curved spacetime isn't curved space and time, it's a curvature in your plot of measurements of distance and time . For example you place a whole lot of optical clocks at different elevations. The lower clocks go slower, and when you plot all the clock rates, there's a curve in your graph.

Yes, it is arbitrary creation to represent ''curves'' that do not exist in reality.

We as the observers could not relatively ''see'' any possible curvature of ''light''
Quote from: John
We do. We see gravitational lensing.
I apologise my sentence was short, let me re-phrase for you. We as the observers could not relatively ''see'' any possible curvature of ''light'' in the relative ''empty'' space between point sources.
Gravitation lensing is a distortion of the Quanta ''whole'' , the ''whole'' is the ''gin-clear'' you observe that you are ''submerged'' in.
 




So in reply to your post, what of space are you defining is stressed?

Quote from: John
The space around the Earth. The stress-energy- momentum tensor is called what it is for a reason. It "describes the density and flux of energy and momentum in spacetime".

In space-time?  surely you just mean in space and the ''stress'' of some ''matter''?

Otherwise it sounds rather gibberish and without meaning,  maybe I do not understand, what is this ''stress'' directly related too?




No aether exists and space is not of solidity.

Quote from: John
You should read Einstein's Leyden Address where he described space as the aether of general relativity.

A space without an ether is not unthinkable.



Quote from: John
General relativity really does treat space like a gin-clear ghostly elastic solid.

''Light'' is the ghostly gin-clear  ''convertual electro-elasticity'' and the reason you ''see'' gin-clear is because you evolved to ''see through it''.

Space is absolute darkness that is interwoven with ''light'' , (but nobody listens to me and of course I am not a scientist).

« Last Edit: 02/06/2016 17:23:02 by Thebox »

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #31 on: 02/06/2016 18:12:47 »
Here I am still waiting for John to explain continuum mechanics. I thought at least he would show me how it could be used to derive general relativity but alas no. Maybe he just hasn't noticed the posts. Maybe he just doesn't know continuum mechanics and is just trying to show off using big words.
Fixation on the Einstein papers is a good definition of OCD.

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Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #32 on: 02/06/2016 18:23:45 »
Here I am still waiting for John to explain continuum mechanics. I thought at least he would show me how it could be used to derive general relativity but alas no. Maybe he just hasn't noticed the posts. Maybe he just doesn't know continuum mechanics and is just trying to show off using big words.

He can't Richard Feynman the great physics and scientist who was part of the Los Alamos team on the Manhattan project to create an atomic bomb once quoted and I believe him

"Now one understands quantum mechanics"
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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #33 on: 02/06/2016 19:08:24 »
Did you not notice the word continuum in there? It can't be about quanta if it is continuous. Therefore no need to invoke Feynman. Careful reading skills can be a real asset.
Fixation on the Einstein papers is a good definition of OCD.

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #34 on: 02/06/2016 19:56:52 »
Well John I'd better get back to reading the pop science by all those PhD's and their pesky textbooks. Full of all those strange symbols that I know are like kryptonite to you.
Fixation on the Einstein papers is a good definition of OCD.

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Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #35 on: 02/06/2016 20:24:46 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #36 on: 02/06/2016 20:42:53 »
Well I have had my feet up with a coffee watching John talk about light going round in circles. Very informative. Now I really know what an electron is. Is that what they mean by spinor?

https://m.youtube.com/watch?v=56w2I8fXDAw
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Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #37 on: 02/06/2016 20:53:38 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

That the universe is infinite has the shape of a donut, our balloon or disk shaped, is just speculation your supposed theory is just an added speculation, with out any evidence to support a real viable final fact later.

Space does not contain matter so it might have extended out into infinite an void, with Alan Guth inflation theory, keeping space time separate from the infinite void, I admit I am speculation not postulating a unprofitable so called theory

Alan
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #38 on: 02/06/2016 21:49:27 »
Actually, I agree with him. In his defense he did say "according to theory", which is a pretty accurate statement as far as I know.
The trouble with this is that the theory is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". This assumption says wherever you are, space will look the same in all directions. But it isn't scientific. For all we know, some guy 46 billion light years away sees one half of the night sky as completely black. Or as a mirror image of the other. Or something else. We just don't know.
 
Almost any analogy can work in-so-far as its intended breadth and depth...
One analogy used to explain an edge-less expanding universe is the balloon analogy. I don't like it because we have no evidence of any higher dimensions, and no evidence of any kind of curvature that would cause you to go round in great big circles. Hence I prefer the raisin-cake analogy. And I note that a raisin cake has  an edge.

John can you tell me why k is not treated as complex in the FLRW metric?
Fixation on the Einstein papers is a good definition of OCD.

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Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #39 on: 02/06/2016 22:08:08 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

That the universe is infinite has the shape of a donut, our balloon or disk shaped, is just speculation your supposed theory is just an added speculation, with out any evidence to support a real viable final fact later.

Space does not contain matter so it might have extended out into infinite an void, with Alan Guth inflation theory, keeping space time separate from the infinite void, I admit I am speculation not postulating a unprofitable so called theory

Alan
Once again, you have absolutely no idea what you're talking about. The nature of the universe is based on general relativity and the Cosmological Principle (an axiom based on observations of the distribution of galaxies in the visible universe). That's why I keep saying that this is the way is based on theory and not mere speculation. From that and the measured density of matter in the universe the shape of the universe is determined. There's no speculation involved.

Since you keep making unfounded accusations and thus appear to have no real interest in learning what theory predicts and keep claiming that predictions are all speculation I can no longer justify either reading or responding to your comments. Welcome to my ignore list. You'll be in the company of the likes of John Duffield et al.

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #40 on: 02/06/2016 22:32:57 »
The nature of the universe is based on general relativity and the Cosmological Principle (an axiom based on observations of the distribution of galaxies in the visible universe).
Like I was saying above, the Cosmological Principle is "the notion that the distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale". This is abused to claim that all observers will see galaxies all around them, and that the universe must therefore infinite. It just isn't scientific. 

Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
Since you keep making unfounded accusations and thus appear to have no real interest in learning what theory predicts and keep claiming that predictions are all speculation I can no longer justify either reading or responding to your comments. Welcome to my ignore list. You'll be in the company of the likes of John Duffield et al.
Alan, it is speculation. If it wasn't, pmb would be able to respond to what I said, and give you some references. He can't.

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #41 on: 02/06/2016 22:49:57 »
Duh! You are on pmb's ignore list so he doesn't even see your posts. You are smart enough to know that too. You want people to believe Pete can't respond because you are right. More disinformation that I won't let you get away with John. I noticed you are on a temporary ban elsewhere is that why you have dropped in here? BTW you didn't answer the question about the value k.
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Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #42 on: 03/06/2016 03:56:02 »
Duh! You are on pmb's ignore list so he doesn't even see your posts. You are smart enough to know that too. You want people to believe Pete can't respond because you are right.
There has never been and will never been anything that John can claim that is contrary to accepted physics that I can't prove him wrong. And you're quite right, Jeff. He is on my ignore list and he knows it!!!

Jeff: What's this nonsense that John is now claiming that I can't respond to? That's really a silly claim because anybody can respond to anything so its not really a challenge when stated like that. If you'd like,. Jeff, I'll explain why John is wrong.

The people on my ignore list are on it for either or both of two reasons (1) the member is rude and/or (2) is incapable of understanding explanations given to him. John's understanding of physics is extremely bad. He actually thinks that there's no such thing as negative energy. He also thinks that just because the electric and magnetic field are parts of the EM tensor aka Faraday tensor that there's no such thing as an electric or magnetic field, which is insanely wrong. In fact its simple to see that one can't even define or measure the Faraday tensor if in fact those fields don't exist.
« Last Edit: 03/06/2016 04:04:26 by PmbPhy »

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Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #43 on: 03/06/2016 05:07:59 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

That the universe is infinite has the shape of a donut, our balloon or disk shaped, is just speculation your supposed theory is just an added speculation, with out any evidence to support a real viable final fact later.

Space does not contain matter so it might have extended out into infinite an void, with Alan Guth inflation theory, keeping space time separate from the infinite void, I admit I am speculation not postulating a unprofitable so called theory

Alan
Once again, you have absolutely no idea what you're talking about. The nature of the universe is based on general relativity and the Cosmological Principle (an axiom based on observations of the distribution of galaxies in the visible universe). That's why I keep saying that this is the way is based on theory and not mere speculation. From that and the measured density of matter in the universe the shape of the universe is determined. There's no speculation involved.

Since you keep making unfounded accusations and thus appear to have no real interest in learning what theory predicts and keep claiming that predictions are all speculation I can no longer justify either reading or responding to your comments. Welcome to my ignore list. You'll be in the company of the likes of John Duffield et al.

You must admit that the theory might be totally wrong?
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #44 on: 03/06/2016 12:59:02 »
Jeff: What's this nonsense that John is now claiming that I can't respond to? That's really a silly claim because anybody can respond to anything so its not really a challenge when stated like that. If you'd like,. Jeff, I'll explain why John is wrong.
No you won't, because I'm not wrong. Here, let me reiterate:

The trouble with this is that the theory is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". This assumption says wherever you are, space will look the same in all directions. But it isn't scientific. For all we know, some guy 46 billion light years away sees one half of the night sky as completely black. Or as a mirror image of the other. Or something else. We just don't know.
 

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Offline jeffreyH

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Re: Does the universe have an edge?
« Reply #45 on: 03/06/2016 13:12:19 »
John you have no idea what the FLRW metric is. You have simply picked up a sound bite.
Fixation on the Einstein papers is a good definition of OCD.