But that is separate from Farsight's own fiction that GR makes an infinite expanding universe impossible. Farsight has nothing besides his conviction to support this claim.
At Rest with our Hubble view
- Thread starter quantum_wave
- Start date
He said that an infinite model can't expand, and it may be a misconception, but it is one I share. I'm considering "infinite" to mean spatially infinite, i.e. space in three dimensions is boundless infinitely. It seems like a no-brainer that if space is infinite, it can't get any bigger, and so expansion can't be occurring. That certainly is different from saying that an observable patch associated with a big bang in pre-existing space, wouldn't expand locally.
No, it's not that easy. An infinite expanding universe remains infinite as every part of it expands.
Don't be confused by whether the whole universe is "getting bigger" and "getting smaller"... those are concepts that don't really apply to infinities.
When you say that, are you being "theory specific", meaning that it is true within the parameters of a specific theory like general relativity or Big Bang theory? Is the distinction in what space itself is, meaning that in GR for example space can stretch?
No, I think it applies to any infinite measure. You can always add more.
I see what you mean.
I would look at it as if there were infinities by definition, meaning that you cannot get to the end of them.
Anyway, during this lull in activity on the thread, I was contemplating were it has gone in regard to being "at rest" relative to the homogeneity of observables in our Hubble view, i.e. the redshift and CMBR.
There seems to be some agreement and general acceptance with the concepts that we can be at rest relative to the observable inflowing microwave energy that is coming form all directions, and with a generalized red shift in the light spectrum of galaxies and galaxy groups that are moving away in all directions. Though Earth, and even our Milky Way galaxy are in motion relative to the background and relative to the observable redshift, there is some agreement and general acceptance that if we could continually adjust our position in space, we could stay at rest relative to both of those observables.
Further, the time line of discoveries that have occurred after the publication of General Relativity, and that have subsequently been incorporated into Big Bang Theory, introduces a few apparent decision points.
1) The Hubble redshift was easily accommodated because of the cosmological constant that Einstein had included.
2) The CMBR was problematic, but mathematically there was a simple solution. Just add the right amount of faster than light inflation in the first second after the Big Bang and you can causally connect the CMB to the big bang. Without that Inflationary epoch, the CMBR would seem to be unconnected, perhaps some remnant of thermalized background radiation from a history that is as yet unrecognized by the scientific community.
3) The observations that the galaxies and groups are separating at an accelerating rate which has been dubbed "dark energy" has not yet resulted in a modification to Big Bang theory, or is that a misconception on my part?
4) Everything after recombination, aka The Surface of Last Scattering, has been derived from the observations of redshift and CMB. Since neither the redshift nor the CMBR were observable or even in existence in their freedom of motion prior to the end of the opacity, everything in Big Bang theory before that is theory and mathematics.
5) The brief discussion of the nature of infinity has pointed out two perspectives. Something that is infinite can be increased, as in infinitely expanding space that has a starting point but expands infinitely by adding new space. And the other perspective, something can be defined as infinite, as an infinite volume of space that has no starting point and no end, i.e. you cannot add to the end of it because by definition it has no end. The distinguishing difference is whether the existing space can stretch and/or if new space can be added somewhere within the infinite volume. If so, then perspective one applies. If not, then perspective two applies.
There seems to be some agreement and general acceptance with the concepts that we can be at rest relative to the observable inflowing microwave energy that is coming form all directions, and with a generalized red shift in the light spectrum of galaxies and galaxy groups that are moving away in all directions. Though Earth, and even our Milky Way galaxy are in motion relative to the background and relative to the observable redshift, there is some agreement and general acceptance that if we could continually adjust our position in space, we could stay at rest relative to both of those observables.
Further, the time line of discoveries that have occurred after the publication of General Relativity, and that have subsequently been incorporated into Big Bang Theory, introduces a few apparent decision points.
1) The Hubble redshift was easily accommodated because of the cosmological constant that Einstein had included.
2) The CMBR was problematic, but mathematically there was a simple solution. Just add the right amount of faster than light inflation in the first second after the Big Bang and you can causally connect the CMB to the big bang. Without that Inflationary epoch, the CMBR would seem to be unconnected, perhaps some remnant of thermalized background radiation from a history that is as yet unrecognized by the scientific community.
3) The observations that the galaxies and groups are separating at an accelerating rate which has been dubbed "dark energy" has not yet resulted in a modification to Big Bang theory, or is that a misconception on my part?
4) Everything after recombination, aka The Surface of Last Scattering, has been derived from the observations of redshift and CMB. Since neither the redshift nor the CMBR were observable or even in existence in their freedom of motion prior to the end of the opacity, everything in Big Bang theory before that is theory and mathematics.
5) The brief discussion of the nature of infinity has pointed out two perspectives. Something that is infinite can be increased, as in infinitely expanding space that has a starting point but expands infinitely by adding new space. And the other perspective, something can be defined as infinite, as an infinite volume of space that has no starting point and no end, i.e. you cannot add to the end of it because by definition it has no end. The distinguishing difference is whether the existing space can stretch and/or if new space can be added somewhere within the infinite volume. If so, then perspective one applies. If not, then perspective two applies.
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PhysBang
If we can see the CMB we are seeing the whole Universe. We see it as it was in the past, not as it is today. We cannot see the entire evolution of all points in space, but we do see all points in time. We cannot see all of the Universe as it is in the present, but we do see all of the Universe as it was in the past.
It's not fiction Farside is correct, if the Universe had a beginning in time and space(and it did)it cannot be infinite, period.
Layman
We know there was a Big Bang, followed by some sort of inflation, followed by expansion at measurable rates. Not with certainty(there is no such animal)but with confidence, the evidence is overwhelming. And just like certainty we have never found a single infinity in any measurement outside of our math, like vacuum, the Universe abhors infinities, they do not exist outside of the mind. So the size of the Universe IS finite, even if we don't yet know it's size. Unbounded means it has no edges, there is no edge to space, every point is dead center in the Universe. Hard to conceptualize but true.
Einstein thought the Universe was infinite and unchanging(static). He was wrong(as he learned well before his death). Finite exists automatically if spacetime had a beginning(and it did). Unbounded is a result of time being a distance just like the other three dimensions. Each point in space time has existed since the BB(a distance of 13.7 billion light years at the current time), each point in space was once in the center of the singularity and each saw the inflation and expansion as being centered on itself(because it was). So NO point can be on an edge, thus unbounded.
There's that "proof" word again. Anyone who uses that word in a scientific conversation has a poor understanding of science.
And the consensus of almost all Cosmologists is that the BB happened(thus the Universe had a beginning). If it had a beginning it cannot be infinite in space or time(thus finite, there's only the two choices, you know). And I explained what unbounded means, if the BB happened then no point in space can be on an edge, they are all in the center of the Universe(give or take a few light years)and have been since the beginning of time.
At the time the CC was created Einstein had no idea that the Universe was expanding, he created the term to keep his infinite and static Universe from collapsing due to gravity. We now know that momentum(at first) and Dark Energy(later)are forces that are stopping the collapse.
quantum_wave
I've seen it, but do not understand how to post it.
It's a simple two axis graph with rate of expansion in the vertical and time in the horizontal. When the BB happened(and after inflation)the rates were the highest but slowing over time due to gravity, in the middle period the rate of the slowing of the rate of expansion leveled out as gravity and DE became more equal in influence, in the latest era the rate of expansion is accelerating as DE becomes stronger than gravity(per unit volume, gravity is sensitive to density(more mass more gravity), DE seems to be constant(for a given volume of space)). It is a smooth sine wave on the graph.
All of the change can be because the density of the early Universe was high, leading to the effects of gravity being high. As the density dropped gravity became less of an influence and the Dark Energy force that was overwhelmed earlier started being more influential, eventually the Universe crossed the point where gravity and DE were balanced and the rate of expansion started rising. Current thought(hypotheses based on the data)says the rate of expansion will increase in the future, maybe even to higher rates than existed right after the BB, leading to us eventually being alone, unable to see any other source of light(gravity bound structures(galaxies and groups of galaxies)seem to be exempt from this type of increase in acceleration, they are still dominated by gravity. DE represents about three quarters of the mass of the Universe, matter and Dark Matter(and thus gravity)the other quarter. Where mass is dense gravity is stronger, where it is thin, DE dominates.
Grumpy
If we can see the CMB we are seeing the whole Universe. We see it as it was in the past, not as it is today. We cannot see the entire evolution of all points in space, but we do see all points in time. We cannot see all of the Universe as it is in the present, but we do see all of the Universe as it was in the past.
It's not fiction Farside is correct, if the Universe had a beginning in time and space(and it did)it cannot be infinite, period.
Layman
We know there was a Big Bang, followed by some sort of inflation, followed by expansion at measurable rates. Not with certainty(there is no such animal)but with confidence, the evidence is overwhelming. And just like certainty we have never found a single infinity in any measurement outside of our math, like vacuum, the Universe abhors infinities, they do not exist outside of the mind. So the size of the Universe IS finite, even if we don't yet know it's size. Unbounded means it has no edges, there is no edge to space, every point is dead center in the Universe. Hard to conceptualize but true.
Einstein thought the Universe was infinite and unchanging(static). He was wrong(as he learned well before his death). Finite exists automatically if spacetime had a beginning(and it did). Unbounded is a result of time being a distance just like the other three dimensions. Each point in space time has existed since the BB(a distance of 13.7 billion light years at the current time), each point in space was once in the center of the singularity and each saw the inflation and expansion as being centered on itself(because it was). So NO point can be on an edge, thus unbounded.
There's that "proof" word again. Anyone who uses that word in a scientific conversation has a poor understanding of science.
And the consensus of almost all Cosmologists is that the BB happened(thus the Universe had a beginning). If it had a beginning it cannot be infinite in space or time(thus finite, there's only the two choices, you know). And I explained what unbounded means, if the BB happened then no point in space can be on an edge, they are all in the center of the Universe(give or take a few light years)and have been since the beginning of time.
At the time the CC was created Einstein had no idea that the Universe was expanding, he created the term to keep his infinite and static Universe from collapsing due to gravity. We now know that momentum(at first) and Dark Energy(later)are forces that are stopping the collapse.
quantum_wave
I've seen it, but do not understand how to post it.
It's a simple two axis graph with rate of expansion in the vertical and time in the horizontal. When the BB happened(and after inflation)the rates were the highest but slowing over time due to gravity, in the middle period the rate of the slowing of the rate of expansion leveled out as gravity and DE became more equal in influence, in the latest era the rate of expansion is accelerating as DE becomes stronger than gravity(per unit volume, gravity is sensitive to density(more mass more gravity), DE seems to be constant(for a given volume of space)). It is a smooth sine wave on the graph.
All of the change can be because the density of the early Universe was high, leading to the effects of gravity being high. As the density dropped gravity became less of an influence and the Dark Energy force that was overwhelmed earlier started being more influential, eventually the Universe crossed the point where gravity and DE were balanced and the rate of expansion started rising. Current thought(hypotheses based on the data)says the rate of expansion will increase in the future, maybe even to higher rates than existed right after the BB, leading to us eventually being alone, unable to see any other source of light(gravity bound structures(galaxies and groups of galaxies)seem to be exempt from this type of increase in acceleration, they are still dominated by gravity. DE represents about three quarters of the mass of the Universe, matter and Dark Matter(and thus gravity)the other quarter. Where mass is dense gravity is stronger, where it is thin, DE dominates.
Grumpy
I keep thinking of those time line graphics like from this link http://www.damtp.cam.ac.uk/research/gr/public/bb_history.html#sc :I've seen it, but do not understand how to post it.
It's a simple two axis graph with rate of expansion in the vertical and time in the horizontal. When the BB happened(and after inflation)the rates were the highest but slowing over time due to gravity, in the middle period the rate of the slowing of the rate of expansion leveled out as gravity and DE became more equal in influence, in the latest era the rate of expansion is accelerating as DE becomes stronger than gravity(per unit volume, gravity is sensitive to density(more mass more gravity), DE seems to be constant(for a given volume of space)). It is a smooth sine wave on the graph.
All of the change can be because the density of the early Universe was high, leading to the effects of gravity being high. As the density dropped gravity became less of an influence and the Dark Energy force that was overwhelmed earlier started being more influential, eventually the Universe crossed the point where gravity and DE were balanced and the rate of expansion started rising. Current thought(hypotheses based on the data)says the rate of expansion will increase in the future, maybe even to higher rates than existed right after the BB, leading to us eventually being alone, unable to see any other source of light(gravity bound structures(galaxies and groups of galaxies)seem to be exempt from this type of increase in acceleration, they are still dominated by gravity. DE represents about three quarters of the mass of the Universe, matter and Dark Matter(and thus gravity)the other quarter. Where mass is dense gravity is stronger, where it is thin, DE dominates.
Grumpy
Does anyone know what the width of the funnel represents?
Yes, I get it now. So the funnel is a history of expansion and the rate can be seen as the change in the width. Thanks.Something like this?
Just a quick sketch looking down the funnel:
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Do you have a reference for this? This seems like it would be a tantalizing discovery. I could only guess that you just made that up yourself.
According to what pseudoscience theory?
Say someone had a basket of oranges and a basket of apples. They then gave you the basket of oranges. Does that mean that there are only baskets of oranges and basket of apples do not exist? There is no proof in this type of logic. Time itself is also on a constant march to infinity.
Unbound just means that it doesn't curve around back on itself. It is not bound or tied up. A bound universe would also not have visible edges from within that universe.
A bound or unbound universe model doesn't have a visible edge in each of them. As far as I know no one has been able to rule out one of these possibilities. Either model would be accepted as a theoretical possibility since one way or the other cannot be proven by any known means.
I think it would be good for you to learn that word. Science would be nothing without mathematical proof. I think accepting this line of rubbish would be more or less just saying that science could just be whatever you want it to be and that it doesn't matter if there is a real reason behind it or not. I would have to say that your understanding of this science is very poor because of your inability to accept scientific proofs.
The consensus is that the BB happened, and that it cannot be determined if it is infinite.
Even though there are only two choices here, I would think you would most likely pick the wrong one.
Yes?
I have no idea where you are getting this from, but it's simply not true. Each time we look at the CMB, we are looking at a new place. Essentially, every ten years we are seeing CMB from about ten light years farther away. If the universe is infinite, we'll keep seeing new areas of the universe that are releasing the radiation we call the CMB. If the universe is finite, we'll eventually see the same areas again.
This is just a fiction. It's a very persistent myth among the pop science types, I guess, but it has no basis in physics. An infinite universe can have a finite past, too. Any intro cosmology text covers this. The WMAP website covers this.
The Big Bang theory is not the expansion of a finite thing. It is a global expansion of space itself over time. Roughly speaking, even if that space is infinite, it still comes out of a singularity in the past.
This is simply mysticism. It's fine if you want to take this metaphysical position, but there doesn't seem to be any reason to adopt it.
Layman
It isn't a discovery, it is our present understanding in Cosmology.
What is the CMB? It is the glow of the Big Bang(actually 300,000 years after the BB)released by the surface of last scattering and shifted into the microwave spectrum by the expansion of space since then. If one knows the math, one could estimate the distance to the CMB simply by measuring it's frequency/temperature. The point is that the CMB is the furthest thing it is even possible to see, and we can still see it, everything else that exists is closer to us(actually, it only appears to be closer). Now, most of it is far in the past(cosmologically, time is a distance)and what we see is no longer there, it has evolved just like our neighborhood has since then and it has also expanded greatly so it's present size(which we cannot see)is much bigger than we measure the Universe to be today. It might be that the CMB is presently expanding faster than light speed, if so we will never be able to see those places as they are today, they are currently over our light horizon. But that appearance is far in our future. Right now we can see the entire Universe's history, the further away the further back in time and those things furthest from us appear as they were at the beginning. Time is a distance, the radius in time is 13.8 billion(give or take), but prior to the CMB there was a millisecond or two of huge rates of expansion called inflation. Depending on which theory you think correct the Universe is about 93 billion lys in diameter(as it actually exists today), but the light time diameter is about 28 billion lys(IE what presently appears 13.8 billion lys away is actually more like 46.5 billion lys away, today, if we could see it).
Grumpy
It isn't a discovery, it is our present understanding in Cosmology.
What is the CMB? It is the glow of the Big Bang(actually 300,000 years after the BB)released by the surface of last scattering and shifted into the microwave spectrum by the expansion of space since then. If one knows the math, one could estimate the distance to the CMB simply by measuring it's frequency/temperature. The point is that the CMB is the furthest thing it is even possible to see, and we can still see it, everything else that exists is closer to us(actually, it only appears to be closer). Now, most of it is far in the past(cosmologically, time is a distance)and what we see is no longer there, it has evolved just like our neighborhood has since then and it has also expanded greatly so it's present size(which we cannot see)is much bigger than we measure the Universe to be today. It might be that the CMB is presently expanding faster than light speed, if so we will never be able to see those places as they are today, they are currently over our light horizon. But that appearance is far in our future. Right now we can see the entire Universe's history, the further away the further back in time and those things furthest from us appear as they were at the beginning. Time is a distance, the radius in time is 13.8 billion(give or take), but prior to the CMB there was a millisecond or two of huge rates of expansion called inflation. Depending on which theory you think correct the Universe is about 93 billion lys in diameter(as it actually exists today), but the light time diameter is about 28 billion lys(IE what presently appears 13.8 billion lys away is actually more like 46.5 billion lys away, today, if we could see it).
Grumpy
You seem very convinced that it is, but you are regurgitating mangled versions of pop science. Some of your stuff is correct, some has some signal-to-noise problems one expects from imperfect copies.
No!
This "glow of the Big Bang" thing is a stupid pop science metaphor. There really is no big bang in the Big Bang theory. The supposed initial singularity plays absolutely no role in the description of the universe used in cosmological investigations.
The CMB is the result of a past that was very hot and very dense, but not compressed into a single point, so to speak. The universe was so hot that photons could not travel far without hitting some particle. At a certain point, the density dropped so that photons could travel without hitting something. We are seeing these first free photons as the CMB. The photons have characteristics that reflect the particles they were interacting with, so we can use these photons to get information about the state of the universe at the time (and locations) they were released.
It is insanely more complicated than that. Plus one has to make a number of assumptions about the universe and about the distribution of matter in the early universe. These are challenges, but not insurmountable.
The expansion rate was slowing for the ~first 5 billion years, becoming neutral in the ~next 5 billion and has started to accelerate in the last few billion. Plotted on a graph it makes a sine curve. In the beginning ours was a gravity dominated Universe, today it is dominated by DE and that will only get worse in the future.
Grumpy
Something like this?
Grumpy, your comment about the expansion rate seems to have been pretty accurate, given the change in diamenter of the "funnel".
AlexG
Nice, I've seen this before and it contains a lot of information and if you look at the top and bottom of the graph(this is a 1D+time representation of a 3D+time reality)you will see the sine I meant.
quantum_wave
That's a pretty accurate representation, you can see the deceleration after Inflation, followed by a period of changing rates and accelerating at the end, though the changing width probably represents total size(which only effects the slope of the sine on the graph), it still shows what I was trying to say. In addition it perfectly illustrates how time is a distance in Cosmology.
Grumpy
Nice, I've seen this before and it contains a lot of information and if you look at the top and bottom of the graph(this is a 1D+time representation of a 3D+time reality)you will see the sine I meant.
quantum_wave
That's a pretty accurate representation, you can see the deceleration after Inflation, followed by a period of changing rates and accelerating at the end, though the changing width probably represents total size(which only effects the slope of the sine on the graph), it still shows what I was trying to say. In addition it perfectly illustrates how time is a distance in Cosmology.
Grumpy
Now there is an informed version of the sequence of events according to the current cosmological model.
The hot and very dense past that is portrayed in many of the popular media descriptions of BBT is also portrayed as a condition after the initial event, but still within the first micro second, I believe. In theory the hot dense "ball" was preceded by some symmetry breaking and matter/antimatter annihilation, as I understand it.
The "compressed into a single point" is what I, as a laymen, seem to see as "implied" as the condition at t=0, but I don't think that is actually part of the theory. Is that what you are indicating,
During the hot dense opacity, I have seen the term "scattering" use to describe the absorption and reradiation of the "confined" photon energy; is that an acceptable layman picture before the recombination?
If I am with you after that, the photons were "freed" from the confinement of opacity, and started to radiate at the speed of light form the entire volume encompassed by the universe at the time of recombination. If I understand correctly, we are still seeing that radiation that was released about 13.3 billion years ago. Does that mean that the whole volume of the universe was so large that CMB radiation that set out 13.3 billion years ago from all directions is still coming without let up and still observed from all points within the observable universe?
I guess there is some difference of opinion about what the diamenter or volume of the universe was at the point of recombination, but is it safe to say it was a finite volume?
My question is, since the model says that the background temperature was ~3000 degrees at the release of the CMB, can you describe the causes of the decline from 3000K to ~2.7K, i.e, is it just expansion, or is it stretching of space? Or is expansion and stretching the same thing?