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Relativity with regard to CMBR and galaxy types


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I have two yes/no questions:


Would an observer, from any random galaxy in the entire universe…

1. measure the exact same temperature of the CMBR?
2. observe the same quasars that we observe, and qualify them as quasars as well?

1. yes/no
2. yes/no

Edited by MarkE
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13 minutes ago, Bufofrog said:

I believe the answers are:

1.  No.

2.  No.

What does that imply for the shape of the universe?
Could it be closed? Could it be finite?
 

"What is the 3-manifold of comoving space, i.e. of a comoving spatial section of the universe, informally called the "shape" of the universe? Neither the curvature nor the topology is presently known, though the curvature is known to be "close" to zero on observable scales. The cosmic inflation hypothesis suggests that the shape of the universe may be unmeasurable, but, since 2003, Jean-Pierre Luminet, et al., and other groups have suggested that the shape of the universe may be the Poincaré dodecahedral space. Is the shape unmeasurable; the Poincaré space; or another 3-manifold?
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics

"As for geometry, space may be flat and obey the laws of Euclidean geometry, or it may be curved. The curvature may be negative, in which case parallel light beams diverge and the universe is open; or it may be positive, in which case the beams ultimately converge like lines of longitude on a globe and the universe is closed".
https://physicsworld.com/a/quintessence/ 

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9 minutes ago, MarkE said:

What does that imply for the shape of the universe?

Nothing as far as I can tell.

 

10 minutes ago, MarkE said:

Could it be closed? Could it be finite?

Could be.

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Posted (edited)
5 hours ago, Bufofrog said:

Nothing as far as I can tell.

 

Could be.

I think it does: the further away you travel from the Milky Way into deep space (theoretically speaking of course), the further you travel into the past, and therefore the closer you’d approach the Big Bang itself, i.e. the ‘initial singularity’, when there was no space or time, nothing at all, and thus you’re predicting a non-physical boundary, a furthest atom away from us, if you will, instead of space continuing forever. Your stance implies a finite universe, and that all the atoms could be counted, because there is a non-infinite amount of atoms present. 
Or maybe I’ve interpreted what you meant the wrong way? Well, at least I don’t see a way in which your stance, especially with regard to different observers being closer or further away from the source of the CMBR, could be compatible with the Milky Way being present in an curved, hypersphere-like infinite universe, which continues on forever, and where no observer is closer to any beginning or end, because in that case we would all be equally close to everything, even to the CMBR.

If I’m wrong in making this inference, could you please explain to me how you visualize the universe for yourself? Maybe you could draw it on a piece of paper, and then tell me what you drew? In your drawing, what lies beyond the furthest atom away from us? (And again, if there is no furthest atom, then you should have answered “yes” at least once).

Edited by MarkE
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7 hours ago, MarkE said:

Would an observer, from any random galaxy in the entire universe…

1. measure the exact same temperature of the CMBR?
2. observe the same quasars that we observe, and qualify them as quasars as well?

1. yes/no
2. yes/no

My answers as I understand the mainstream science*. 

1: no
2: no

1: Their map of the subtle fluctuations in temperature would look different. The average temperature of their CMBR measurement could be very similar to the temperature we measure, if we assume they perform their measurements are done at present times. A measurement performed much earlier or later would deviate from our current measurements. If universe continues to expand the cosmic microwave background will continue redshifting.

2: The quasars we observe may not be visible at another location random location. Line of sight and distance are two factors that I think of. 

 

*) https://en.wikipedia.org/wiki/Cosmic_microwave_background

 

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4 hours ago, MarkE said:

I think it does: the further away you travel from the Milky Way into deep space (theoretically speaking of course), the further you travel into the past, and therefore the closer you’d approach the Big Bang itself

Absolutely not.  You always travel into the future.  The reason that stars far from earth are seen as they were in the past is because the light that is just now reaching us left the star long ago.  The light from the sun shows us what the sun looked like 8 minutes in the past.

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I will say 

yes
no

We measure the temp of the CMBR to deviate 2 parts in 10000, once the motion of our galaxy/sun/planet has been factored out, which blue shifts the CMB ahead of our path, and red shifts the CMB behind our path. 
I see no reason why anyone in the universe would measure any larger deviations.

As for the quasars , someone in a galaxy 10 billion light years away might see our galaxy as it was 10 billion years ago, when its central BH was active and producing the large jets associated with quasars.

Edited by MigL
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17 hours ago, MarkE said:

the further away you travel from the Milky Way into deep space (theoretically speaking of course), the further you travel into the past, and therefore the closer you’d approach the Big Bang itself,

Look, not travel. If you observe a galaxy 1 billion LY from us, you are seeing it as it was roughly 1 billion years ago (there will be some discrepancy owing to motion and expansion) Images from e.g. Hubble from very distant galaxies are looking far into the past, i.e. close to the BB. But travel? No.

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8 hours ago, MigL said:

We measure the temp of the CMBR to deviate 2 parts in 10000, once the motion of our galaxy/sun/planet has been factored out, which blue shifts the CMB ahead of our path, and red shifts the CMB behind our path.

I completely agree.  I answered the question assuming the poster was not asking about factoring out the observers motion.  That is the danger of asking a yes or no question about a nuanced situation.

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You're right.
I made the unwarranted assumption that anyone who can measure the CMB temp ( and deduce its origins ), would know about frequency shifting and galactic motion.
I believe the CMB was discovered accidentally, so it could have happened before we realized there was galactic motion, or even galaxies.

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Posted (edited)

Could anyone here actually draw ✏️ the universe on a piece of paper?

it must be possible, because we can also draw the Solar System, or the Local Group, so why not larger scales? So, is there anyone here who is able to make a rough sketch of how the entire universe would look like?

In discussions on the shape of the universe I always read arguments such as: “a three dimensional manifold that is bounded by a three dimensional sphere, that is in turn contained by the four dimensional spacetime manifold”,  or something close to the “surface of a balloon”-analogy (which I think is a very bad example, because there can be only a surface if there’s also an inside, which the universe supposedly doesn’t have), but nobody ever tries to actually make that description visible.

Is there anyone here who can make this visible? Or just explain in words your drawing, that’s also fine. If this turns out to be impossible, it’s hard for me to take those kind of theoretical arguments very seriously. I hope I’m not the only one.

Edited by MarkE
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1 hour ago, MarkE said:

Could anyone here actually draw ✏️ the universe on a piece of paper?

it must be possible, because we can also draw the Solar System

The universe is 3-D. The solar system is approximately 2-D, with far fewer moving parts. 

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On 7/22/2021 at 1:51 PM, Bufofrog said:

That is the danger of asking a yes or no question about a nuanced situation.

I agree. I also agree to @MigLs "yes" answer and the motivation. My "no" answer assumed that the question's "exact" requires that any patterns in the small temperature fluctuations are identical; that a detailed all-sky picture of CMBR would be independent of location.  In the words: I assume that an image, such as the on based on WMAP data below, will may not be exactly the same if the data was gathered in a very distant location from our galaxy.

101080_7yrFullSky_WMAP_320W.jpg

(Source: https://map.gsfc.nasa.gov/media/121238/index.html)

 

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10 hours ago, MarkE said:

In discussions on the shape of the universe I always read arguments such as: “a three dimensional manifold that is bounded by a three dimensional sphere, that is in turn contained by the four dimensional spacetime manifold”,  or something close to the “surface of a balloon”-analogy (which I think is a very bad example, because there can be only a surface if there’s also an inside, which the universe supposedly doesn’t have), but nobody ever tries to actually make that description visible.

Is there anyone here who can make this visible? Or just explain in words your drawing, that’s also fine. If this turns out to be impossible, it’s hard for me to take those kind of theoretical arguments very seriously. I hope I’m not the only one.

The important thing to remember is that most analogies will have limitations. eg: The blowing up of a balloon analogy [with dots painted on the surface representing galaxies] illustrates that it is spacetime expanding, not the dots [galaxies] flying away from other dots [galaxies] It is a 2D illustrataion representing 3D space, or 4D spacetime. The better analogy [but still with limitations] is the raisin loaf analogy. The 3D dough representing 3D space [or 4D spacetime] and the raisins representing galaxies.

Both analogies of course fail at explaining the gravitational effects of closely bound galaxies, groups of galaxies, and galactic walls, that overcome the expansion of space, due to the local  density of different regions. The  expansion is only seen over larger scales.

On 7/22/2021 at 1:05 PM, MigL said:

I will say 

yes
no

I agree.

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On 7/22/2021 at 2:33 AM, MarkE said:

I think it does: the further away you travel from the Milky Way into deep space (theoretically speaking of course), the further you travel into the past, and therefore the closer you’d approach the Big Bang itself, i.e. the ‘initial singularity’, when there was no space or time, nothing at all, and thus you’re predicting a non-physical boundary, a furthest atom away from us, if you will, instead of space continuing forever.

No, that’s wrong.

It is only when you are observing from Earth (like through telescopes) of some distant objects (like galaxies) in space, that you are looking those objects from the past of something that already happened. This is because what you are observing take long time to reach our telescopes.

but you are talking about space travel. That’s different. 

As you travel, you will only experience the present...you don’t travel back in time. You cannot go to the BB singularity through space travel.

 

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On 7/23/2021 at 7:44 AM, MarkE said:

Could anyone here actually draw ✏️ the universe on a piece of paper?

it must be possible, because we can also draw the Solar System, or the Local Group, so why not larger scales? So, is there anyone here who is able to make a rough sketch of how the entire universe would look like?

Universe.png.f1924a730fd5bb581c0e8d3cc2e11e5e.png

Could represent Observable Universe like this. We are at some point on the blue line. Gray lines representing all other big gravitationally bound regions are curving away or separating from us(or from their perspective, we from them).

What we see of this will depend on whatever light has presently been able to reach us and what there is to actually see.

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  • 2 weeks later...
On 7/26/2021 at 8:35 PM, Endy0816 said:

Universe.png.f1924a730fd5bb581c0e8d3cc2e11e5e.png

Could represent Observable Universe like this. We are at some point on the blue line. Gray lines representing all other big gravitationally bound regions are curving away or separating from us(or from their perspective, we from them).

What we see of this will depend on whatever light has presently been able to reach us and what there is to actually see.

First of all, thanks for providing a visualization! It really helps a discussion about the shape of the universe, instead of approaching the subject exclusively by using words and mathematics alone, because the universe must have an overall shape, which must be visualizable.

I have a few question regarding the above image:
1. What exactly explains this linear direction of the Big Bang?
2. What does the dark region surrounding the lines represent? 
3. Does this imply that a space traveller, at some point after travelling in any arbitrary direction, would observe a non isotropic/homogeneous universe?
4. Would any other observer, anywhere in the universe, from their own perspective, also be located at the blue line?


Does everybody here disagree with this depiction? @swansont ? @studiot? @Bufofrog The rest?
Would you prefer a universe that looks more spherical instead, somewhat like a globular cluster? If so, why (not)?

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On 7/22/2021 at 2:33 AM, MarkE said:

I think it does: the further away you travel from the Milky Way into deep space (theoretically speaking of course), the further you travel into the past, and therefore the closer you’d approach the Big Bang itself, i.e. the ‘initial singularity’, when there was no space or time, nothing at all, and thus you’re predicting a non-physical boundary, a furthest atom away from us, if you will, instead of space continuing forever. Your stance implies a finite universe, and that all the atoms could be counted, because there is a non-infinite amount of atoms present. 
Or maybe I’ve interpreted what you meant the wrong way? Well, at least I don’t see a way in which your stance, especially with regard to different observers being closer or further away from the source of the CMBR, could be compatible with the Milky Way being present in an curved, hypersphere-like infinite universe, which continues on forever, and where no observer is closer to any beginning or end, because in that case we would all be equally close to everything, even to the CMBR.

If I’m wrong in making this inference, could you please explain to me how you visualize the universe for yourself? Maybe you could draw it on a piece of paper, and then tell me what you drew? In your drawing, what lies beyond the furthest atom away from us? (And again, if there is no furthest atom, then you should have answered “yes” at least once).

As others have said, if you travel in space, to the boundaries of our solar system, to the edge of our local group, to the edges and beyond of the Milky Way, you are not travelling back in time. We do though look back in time, as we view the outer universe because of the finite speed of light. Therefor light from those distant regions take time to reach Earth as an observer.

BUT!! If you are travelling at relativistic speeds, and eventually return to Earth, you will be returning to an Earth in advance of the time that has passed for you. The example I have representing that is if you and I were twins, and I being the more intrepid, took of on a star ship and travelled for 6 months at 99.999%c, then turned around and travelled at the same speed back to Earth where I left you, I would be returing to an Earth around 230 years in the future, while only 12 months have passed on my ship board clocks and my own biological clock. 

41 minutes ago, MarkE said:

First of all, thanks for providing a visualization! It really helps a discussion about the shape of the universe, instead of approaching the subject exclusively by using words and mathematics alone, because the universe must have an overall shape, which must be visualizable.

I have a few question regarding the above image:
1. What exactly explains this linear direction of the Big Bang?
2. What does the dark region surrounding the lines represent? 
3. Does this imply that a space traveller, at some point after travelling in any arbitrary direction, would observe a non isotropic/homogeneous universe?
4. Would any other observer, anywhere in the universe, from their own perspective, also be located at the blue line?


Does everybody here disagree with this depiction? @swansont ? @studiot? @Bufofrog The rest?
Would you prefer a universe that looks more spherical instead, somewhat like a globular cluster? If so, why (not)?

[1] The BB is an intrinsic evolution/expansion of space in all directions.

[2] Analogies have limitations but not sure if that is relevant.

[3]The observable universe is generally isotropic and homogenous in all directions...we have no reason to assume anything different beyond our observable horizon, but who knows?

[4]No, anything in the universe not gravitationally bound, is increasing in distance due to space expansion.

That's my attempt at your questions and what I understand of those questions. 

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1 hour ago, MarkE said:

 

I have a few question regarding the above image:
1. What exactly explains this linear direction of the Big Bang?

It's a graph, with time being on the x-axis. Usually one uses a linear scale, unless there's a compelling reason not to.

1 hour ago, MarkE said:

2. What does the dark region surrounding the lines represent? 

Nothing. It's a graph. Only the lines mean anything.

1 hour ago, MarkE said:

3. Does this imply that a space traveller, at some point after travelling in any arbitrary direction, would observe a non isotropic/homogeneous universe?

No. This has nothing to do with travel. It's different possibilities of how the universe might have evolved after the BB. As Endy said, evidence supports the notion that we evolved along the blue line, rather than one of the others.

1 hour ago, MarkE said:


4. Would any other observer, anywhere in the universe, from their own perspective, also be located at the blue line?


Yes. If we're on the blue line, so is everybody else.

 

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The graph looks wrong to me.  The blue line seems to indicate a situation where as time goes on the size of the universe is constant.  The gray lines above the blue line indicate a universe where space is expanding as time goes on and the gray lines below show a universe that is shrinking over time.  So our universe is one of the upper gray lines.

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18 minutes ago, Bufofrog said:

The graph looks wrong to me.  The blue line seems to indicate a situation where as time goes on the size of the universe is constant.  The gray lines above the blue line indicate a universe where space is expanding as time goes on and the gray lines below show a universe that is shrinking over time.  So our universe is one of the upper gray lines.

I think this depends on what is meant by "space" which is somewhat ambiguous

But it probably doesn't mean volume for this graph, because we should see the volume increase and then decrease for positive curvature, and that's not depicted. And for negative curvature, you don't shrink. AFAIK you wouldn't shrink starting from the BB anyway. I interpreted as depicting curvature. Graphing that over time, however, is...interesting.

 

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Why this insistence on being able to visualize the universe ?

It is bad enough trying to visualize the 3 dimensional volume of the unverse, since we are inside of it, and cannot possibly get to a vantage point to 'view' it externally, but due to the finite speed of light, events are linked, and 'evolve', through time, hence space-time.
This would necessitate a 4 dimensional view; and you expect a depiction on a two dimensional computer screen ?

The best we can do, is reduced dimensionality analogies, like the rubber sheet/bowling ball analogy of gravity, or Endy's space/time graph. but then you run the risk of non-sensical interpretations like "What is pulling down the boling ball to depress the rubber sheet ?", or "What do the black spaces between the lines represent ?".

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Posted (edited)
On 8/5/2021 at 12:16 PM, swansont said:

It's a graph, with time being on the x-axis. Usually one uses a linear scale, unless there's a compelling reason not to.

Nothing. It's a graph. Only the lines mean anything.

No. This has nothing to do with travel. It's different possibilities of how the universe might have evolved after the BB. As Endy said, evidence supports the notion that we evolved along the blue line, rather than one of the others.

Yes. If we're on the blue line, so is everybody else.

 

Then the graph wasn't what I asked for.

I asked whether anyone could draw the shape of the universe on a piece of paper (or explain that drawing in words, which would also suffice). If you can draw the Solar System, and the Milky Way, or the Local Group, it must be possible to make a drawing of the entire universe. If however nobody can do this, then I have a hard time taking the theoretical/mathematical descriptions of that shape too seriously. For all we know these models don't describe the real world, even though they make logical sense.

As Richard Feynman once said:
Make every question you ask in research a question about nature. Otherwise you can waste your life in working out the minutiae of theories that most likely will never have anything to do with nature.”

Lee Smolin adds to this:
"Even worse, we get caught up in petty competitions and academic turf battles between the adherents of different models". 

I'm not saying that I have a clear indication of what the shape of the universe must be, I just think that, if nobody is able to draw it on a piece of paper, there's no leading, widely accepted shape that's more plausible than any other shape. Therefore it could be spherical, like a globular cluster (which would make the most sense to me).

What about you, what shape makes the most sense to you? 

Edited by MarkE
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