The Trouble with Hubble Constant

Now we enter the absurd-ium again.
CTRandall said:
Time is a function of consciousness.
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RJM Corbet said:
Time and space are the impenetrable walls of the room of nature to which we are confined.
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Time as a function only of consciousness would lead to determination that most of physic might also be that.
We measure time and many other things to help us explain physics and we use time to determine the speed of light which in turn might be the speed at which the universe expands. Which would mean in a time is consciousness sense that the universe is only expanding in our mind and then perhaps all of our measurements of gravity and acceleration are in our mind also.

As far as Time and Space as a wall--we use light and radiation to see what is out in time and space so even if we called it a wall it would be one we can see through. However; when we go into space we are in space-time and we travel through it so it is more a medium than a wall. The only real wall is the limitation of the Speed of Light if, in fact, that is the fastest we can travel. If the universe is expanding outward from some-undefined-point then theoretically there might already be parts of the universe that are out of our visible horizon and that would almost be like a wall to the things we can see as at some point, with some parts of the universe traveling away from us, light would cease being able to reach us. Also in theory we would not be able to travel there even if we could travel at the speed of light.

What we measure as time might fall in the conscious level. If we were on a tidally locked world we might have had a different way of determining time. Different measurement.
We probably would have a whole bunch of other problems along with that. We would probably measure time anyway and that would help us determine other thing having to do with physics.

We are measuring something that exist and is real and if we were all removed--if every conscious creature were removed--time would not cease to exist. The universe would go on moving as it is now. Gravity would still work. The planets would still move--none of these things would stop. It would be a waste of some awesome things without anyone to appreciate and to measure it though.
 
tinkerdan said:
if the universe is expanding outward from some-undefined-point
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I think it is expanding outward from everywhere. There is no centre point? The big bang is a point where time and space began, but in all directions? It's somenting we cannot mentally visualise?
tinkerdan said:
the speed of light which in turn might be the speed at which the universe expands.
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I' think the Hubble Constant is the speed st which the universe is exoanding? The further away a galaxy is the faster it appears to be receding from us? I'm not too sure....
 
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RJM Corbet said:
I think it is expanding outward from everywhere. There is no centre point? The big bang is a point where time and space began, but in all directions? It's somenting we cannot mentally visualise?
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There is no center point because we are still inside the Big Bang, so to speak. It's difficult to visualize.

RJM Corbet said:
I think the Hubble Constant is the speed st which the universe is expanding? The further away a galaxy is the faster it appears to be receding from us? I'm not too sure....
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Think of it this way: Space is expanding. The more space you measure, the more expansion you observe. Eventually, given enough space between two objects, they will physically move away from each other faster than the speed of light. This is possible because the two objects (and this is important) are not traveling through space, they are merely being separated by expanding space. Because of this, most of the universe is lost to us, and the amount of it that is observable from any one point will continue to decrease as billions of years go by.

The Hubble Constant is based on the concept that objects will separate from each other at a predictable speed based on the amount of space between them. The speed of separation is non-linear, because the more space you insert between two objects, the faster the speed.

Keep in mind, this effect of expanding space doesn't necessarily apply to galaxies and galaxy clusters. It's not going to make nebulae and planetary systems fly apart. These are held together by close gravitational attraction. It takes a lot of space to cause this separation, and we see it happening at long distances because there's a lot of space out there.

Hope that helps.
 
RJM Corbet said:
Yes. Thank you :)
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The reason for all this is that expansion of the universe has nothing at all to do with General/special relativity. To take a silly analogy, a game of chess on a chess board has a large number of rules that govern how the pieces interact, but there are no rules on how big the board should be. It can be expanded and, of course, the game remains the same. GR are the 'rules' about how mass and spacetime interact but not about how spacetime itself develops.

Currently the points of the universe that are actually moving out of sight are actually quite a distance away ~14.4 billion light years away, so we're not losing most of the current observable universe at the moment thankfully!

Re: the speed the universe could expand at. I think TD is refering to the discovery that the hubble constant is variable and accelerating. I don't think there are any ideas as to why or what value it could get to. But because of above, and our lack of understanding of dark energy and spacetime, there is currently no constraint on it, in fact it could easily be a multiple of the speed of light. But that's bad...

...because one of the postulated ends of the universe is the 'big rip' where the expansion of the universe is allowed to accerelate exponetially. To give an example, if the expansion was at the speed of light then, by my calculations, the size of the observable universe drops to ~3260 light years. Note that that is significantly smaller than the milky way. At this point large scale structures such as milky way galaxies or larger cannot form - remember that the laws of physics of matter are still limited to the speed of light i.e. a planet can only orbit a star if it 'sees' the gravitational effect of the star. If the star drops out of the planet's universe because it's part of an expanding space that is faster than the speed of light it can no longer interact with the star. As the expansion increases this size shrinks further and further till even the electrons in atoms are too distant from their nuclei...and so it continues till everything is ripped apart.
 
Venusian Broon said:
where the expansion of the universe is allowed to accerelate exponetially
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Phil Plait mentions something like this in one of the last Crash Course Astronomy videos - and it can cause a really interesting effect. :)

 
Cool. And while we're here is there any latest knowledge about the shape of the universe? I believe recent opinion is that the universe is flat?
 
Venusian Broon said:
Currently the points of the universe that are actually moving out of sight are actually quite a distance away ~14.4 billion light years away, so we're not losing most of the current observable universe at the moment thankfully!
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Exactly. I misspoke earlier about this. Only the very earliest galaxies are currently lost to us.

RJM Corbet said:
Cool. And while we're here is there any latest knowledge about the shape of the universe? I believe recent opinion is that the universe is flat?
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Here's a rundown on the various ideas circa 2015.

 
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tinkerdan said:
This is the most recent I have heard about.
www.universetoday.com

New Research Suggests that the Universe is a Sphere and Not Flat After All

We have long thought the universe was flat. New research shows it could be curved, and that raises questions about our understanding of the cosmos.
www.universetoday.com www.universetoday.com
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November 6th 2019
"... When the team analyzed the CMB data from the Plank spacecraft, they found the fluctuations were larger than expected. This means that to within a 99% certainty the universe is closed, not flat ... This new research contradicts numerous previous studies showing the universe is flat..."

That was quick. Thanks @tinkerdan :)

EDIT
Nozzle Velocity said:
Here's a rundown on the various ideas circa 2015.

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Thanks @Nozzle Velocity
So ... it seems that four years is a long time in early 21st Century science?
 
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It says in the article:
"The scale of fluctuations in the CMB is determined by the amount of dark matter and dark energy in the universe, which we know, so we know how large the fluctuations should appear."

I know next to nothing about the shape or any other characteristic of the universe and my brain is too small it even begin to understand any of it, but... I remember someone in the field of physics in a documentary mentioning that dark matter and dark energy only exist hypothetically. They have been 'created' to explain the way the universe was holding itself together. Their existence has not (yet) been proven.
I suppose you can hypothetically calculate the amount of dark matter and energy that is required for what it is supposed to do. But basing any further theories on this hypocritical data, as with the CMB data to establish the shape of the universe, seems a bit... premature?

*skulks away, hoping he did not make a fool of himself*
 
Elckerlyc said:
Their existence has not (yet) been proven.
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The existence of the two invisible forces that exercise the effects of dark matter and dark energy have been demonstrated by evidence. What they actually are and were they come from is not known. Vibrations from other dimensions that impact our own? Unknown. But the effects are definite.

The universe IS expanding. It's a weird antigravity force. So they call the effect 'dark energy'. Determined by the Hubble Constant.

There is not enough visible matter to account for the gravity holding galaxies like our own together. I'm swinging a bucket 100 feet out on the end of only 10 feet of rope. What's up? Where's the invisible missing rope? The galaxy should fly apart. So they call it 'dark matter'.

Hope that helps, lol ...
 
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Elckerlyc said:
I suppose you can hypothetically calculate the amount of dark matter and energy that is required for what it is supposed to do. But basing any further theories on this hypocritical data, as with the CMB data to establish the shape of the universe, seems a bit... premature?
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Dark matter has predictable and observable influences on galaxies. We know it's there, but we don't understand its nature. Why can't we see it?

Dark energy is more theoretical. The 2011 Nobel Prize winners discovered the increasing rate of expansion of the universe around 1990. Dark energy was used as a hypothesis to explain that phenomenon. Now those same prize winners are credited by science journalists for "discovering" dark energy. I always thought that process was a little sketchy, but the calculations may very well hold up over time.
 
Thank you, guys, for my ongoing education! ;)
This now also reminded me also of the 3 ways the universe could end: The Big Rip, The Big Chill or The Big Crunch.

Here's another one. I have always pictured The Big Bang simply as an explosion. (I'm sure it is lot more complex as that) The outgoing forces of an explosion would normally be equal in all directions (IOW an expanding sphere), unless there are some other forces or barriers that prevent this from happening.
If the universe was not a sphere but open or flat, as previously thought, what forces could cause that to happen? Assuming there's nothing outside our universe (and if there is we have no inkling of what that could be, anyway) to limit or block expansion in all directions, it must be some force inside. Has this to do with an unequal distribution of dark matter and dark energy?
 
Elckerlyc said:
The Big Bang simply as an explosion. (I'm sure it is lot more complex as that) The outgoing forces of an explosion would normally be equal in all directions (IOW an expanding sphere)
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It's like trying to visualize an explosion from a centre that is everywhere? 'Direction' loses all meaning?
 
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It seems that in spite of the recent Planck mission measurement of a larger lensing of the microwave background than known to date -- there is still lots of debate about the shape of the universe:

There Might Be a Hidden 'Crisis' in What We Know About the Universe - VICE

www-vice-com.cdn.ampproject.org www-vice-com.cdn.ampproject.org

"... According to Planck’s measurements, the CMB is being gravitationally lensed much more than expected. One possible explanation to account for this observation is that there is a curvature woven into the fabric of spacetime.

“A closed Universe can provide a physical explanation for this effect, with the Planck cosmic microwave background spectra now preferring a positive curvature at more than the 99% confidence level,” the team said in the study.

This is a provocative result that complexifies the established idea of the universe’s shape, but the authors emphasize that it will take much more research to confirm whether the Planck data presents a terminal challenge to the flat cosmos.

“In principle, the next CMB experiments such as the Simon's Observatory [in Chile] should answer the question,” Melchiorri said, though he said that would not necessarily be enough.

“Personally, I think we need a new CMB mission like Planck with improved detectors,” he added, such as a concept mission called CORE, which ESA rejected. “In reality, we may end up waiting several years before having a definitive answer.”

In the meantime, the flat universe remains the leading model of our cosmic surroundings. But given that we have barely begun to understand this weird expanding object that we live in, more surprises are sure to come ..."

EDIT
The paper for anyone who can understand it:

 
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RJM Corbet said:
It seems that in spite of the recent Planck mission measurement of a larger lensing of the microwave background than known to date -- there is still lots of debate about the shape of the universe
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Absolutely - the debate has been running for decades. :)
 
More explanation for laymen like me about this new Planck CMB data. November 8th 2019. It's clearly presented and the visuals are nice lol:
10.45
 
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