Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: doughorrigan on 23/03/2021 18:15:37
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I'm curios. As far as I can tell from the scientific literature the universe is about 13.8 billion years old.
No matter which direction we point our telescopes we always get the same answer - the most distant objects in any direction are 13.8 billion light years away.
It's not as though we can see 13.8 billion light years in one direction but only 10 billion in the other, it's 13.8 in every direction.
Which kind of makes this little planet of ours the very centre of the observable universe doesn't it?
Thoughts?
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Which kind of makes this little planet of ours the very centre of the observable universe doesn't it?
Thoughts?
Yes, but everywhere is the centre of the universe.
Imagine drawing dots on a balloon, and then inflating it.
All the dots move away from each other so all of them "see" themselves as the centre.
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Hmm. Not sure I'm convinced about that. There must be stars at the edge of the universe, on the cutting edge so to speak of the big bang that will have stars behind them but none in front of them in their direction of travel?
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There must be stars at the edge of the universe
Why do you assume it has an edge?
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If it doesn't have an 'edge' then what are we measuring to?
If we say that the universe is 13.8 billion years old because that is the furthest we can see, then any stars that are 13.8 billion light years away from us won't have anything beyond them will they?
To ask another silly question - why do I have to go through verification every time I post a question or reply to an answer when I'm already logged in?
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If it doesn't have an 'edge' then what are we measuring to?
The visible Universe has an edge. The Universe as a whole, not necessarily. It could potentially be infinite. Or it could be a hypersphere of finite size (which still wouldn't have an edge).
If we say that the universe is 13.8 billion years old because that is the furthest we can see, then any stars that are 13.8 billion light years away from us
The visible Universe is actually bigger than that because of space expansion (about 93 billion light-years across).
won't have anything beyond them will they?
There's no reason there shouldn't be. Any galaxies beyond a certain point won't be visible because their light hasn't reached us.
To ask another silly question - why do I have to go through verification every time I post a question or reply to an answer when I'm already logged in?
I don't know. I don't have that problem with posting myself. You might want to contact the administrator.
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any stars that are 13.8 billion light years away from us won't have anything beyond them will they?
The 13.8 billion light years is an extrapolation. We can't actually see any individual stars (or individual galaxies) at that distance.
- With current technology, we can spot individual quasars (active galaxies) out to around 13.4 billion light years.
https://en.wikipedia.org/wiki/List_of_the_most_distant_astronomical_objects
Let's just back off to a galaxy that is 13 billion light years away.
- If any astronomer looks through a big telescope, they will be looking backwards in time.
- If an astronomer over there looks in our direction, they will see some old galaxies (one of which may have eventually merged into our Milky Way galaxy)
- If they then turn their telescope in the opposite direction, they will also see galaxies in that direction, too, out to around 13 billion light years
- We cannot see those galaxies from here, but someone suitably positioned can see them.
There is a reason we can't see all the way back to the Big Bang, and that is because the early universe was filled with ionized gas (plasma), which blocks electromagnetic radiation. We see the remnants of this glow (red-shifted by a factor of over 1,000) as the Cosmic Microwave Background Radiation, which comes from all over the sky.
https://en.wikipedia.org/wiki/Cosmic_microwave_background
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Hmm. Not sure I'm convinced about that. There must be stars at the edge of the universe, on the cutting edge so to speak of the big bang that will have stars behind them but none in front of them in their direction of travel?
It sounds like you're assuming that the big bang happened at a point in space, where stuff expanded out into a void. This isn't the accepted model; the *whole universe* was hot and dense at the big bang, and then expanded uniformly, everything flying away from everything else; it didn't expand *into* anything, it just expanded, that is, the space between stuff increased. There was no edge then and there's no edge now.
Wherever you are in the universe, everything is receding from you in all directions. What we call the 'edge' of the universe is just the limit of what we can see; we know that the whole universe is vastly bigger than that (possibly infinite).
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@doughorrigan
Hi there!
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I Understand certain " Models " or
" Hypothesis " seem Incomplete.
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Especially when the subject matter in discussion is of an infinite universal scale.
Thou, there is a special section called " New Theories " where Users are Allowed to discuss topics out of the realms of Reality & can freely state their personal viewpoints or Beliefs.
👍
There is a Topic similar to your OP already out there... Which might Interest you... here's the address...
https://www.thenakedscientists.com/forum/index.php?topic=81928.0
Perhaps the " Verification " requests are a brand new system put in place & enabled on the Forum to avoid Spammers & dishearten them from creating havoc & disrupting the TNS Forum with irrelevant ADs.
👍
(Which is a Really Good thing for all Registered Users)
You are a New Member, hence the Anti - Spam system might be requesting Verifications.
I Believe after a while, it shall Stop automatically.
No Worries!
🙂👍
P.S. - From All of US...Welcome to the TNS Science Forum!
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Hope you enJoy your stay & have a Good time.
🙏
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Hmm. Not sure I'm convinced about that. There must be stars at the edge of the universe, on the cutting edge so to speak of the big bang that will have stars behind them but none in front of them in their direction of travel?
It sounds like you're assuming that the big bang happened at a point in space, where stuff expanded out into a void. This isn't the accepted model; the *whole universe* was hot and dense at the big bang, and then expanded uniformly, everything flying away from everything else; it didn't expand *into* anything, it just expanded, that is, the space between stuff increased. There was no edge then and there's no edge now.
Wherever you are in the universe, everything is receding from you in all directions. What we call the 'edge' of the universe is just the limit of what we can see; we know that the whole universe is vastly bigger than that (possibly infinite).
Suppose the Universe started from a single, concentrated, point, which contained all the matter in existence.
Then, for whatever reason. the point "exploded", and threw the matter out in all directions..
Just as, for example, when a hand-grenade explodes, and throws bits outwards in all directions.
If you observe these bits, and measure their trajectories, you can plot them back, and determine their centre of origin.
In a similar way, these days, we have telescopes of sufficient power to observe galaxies, and measure their trajectories, using Doppler effects.
So couldn't we use these, and other observations, to determine the centre of origin of the Universe.
I mean, if the Universe really did originate from a single point, why shouldn't we able to find where that point was?
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I mean, if the Universe really did originate from a single point, why shouldn't we able to find where that point was?
Which kind of makes this little planet of ours the very centre of the observable universe doesn't it?
Thoughts?
Yes, but everywhere is the centre of the universe.
Imagine drawing dots on a balloon, and then inflating it.
All the dots move away from each other so all of them "see" themselves as the centre.
Now imagine it starting from a very small balloon.
It's not an explosion "in space" but an expansion "of space".
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Isn't your "balloon" analogy fatally flawed BC.
Don't all balloons have a central point from which they expand?
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Isn't your "balloon" analogy fatally flawed BC.
Don't all balloons have a central point from which they expand?
Not from the perspective of an ant on the surface.
You seem to to realise it's an analogy- specifically it's a bit thin on dimensions.
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It's not an explosion "in space" but an expansion "of space
It can be both, can't it?
Can you have two or more objects that undergo expansion of the space between their constituent parts?
They might in theory interact too.
Is there an explanation of the phenomenon whereby the space between objects (galaxies)
increases?
Or is it just that we observe this to be the case and the inflationary model describes the process well?
Also can it be shown that the expansion of space is 100,% uniform?(does it need to be so shown?)
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Light has a finite and constant speed in vacuum. Shortly after the big bang, inflation expanded space at a rate faster than the speed of light. At the edge of the observable universe we are seeing light that was reflected from objects that were separated from us during that inflationary period.
This is other good evidence that the universe had a beginning. If it had always been there there would be no edge to the observable universe. We would simply need better and better telescopes to see further.
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Suppose the Universe started from a single, concentrated, point, which contained all the matter in existence.
Then, for whatever reason. the point "exploded", and threw the matter out in all directions..
Just as, for example, when a hand-grenade explodes, and throws bits outwards in all directions.
If you observe these bits, and measure their trajectories, you can plot them back, and determine their centre of origin.
In a similar way, these days, we have telescopes of sufficient power to observe galaxies, and measure their trajectories, using Doppler effects.
So couldn't we use these, and other observations, to determine the centre of origin of the Universe.
I mean, if the Universe really did originate from a single point, why shouldn't we able to find where that point was?
Good question. Even in Newtonian physics you can't tell. If you were on one of those bits exploding from the grenade, all the pieces would appear to be receding directly away from you at a pace in proportion to its distance. Every point would appear to be as much the center as any other and there would be no obvious way to locate the point in space of the explosion. It would be completely dependent on the arbitrary choice of reference frame.
So in this sense, the explosion-from-a-point-into-empty-space model seems to generate the same observations as one with nothing really moving and space expanding uniformly. But space is not expanding uniformly, and the sort of recession speeds you'd get from an explosion into empty space would not result in accelerated recession rates or in event horizons. Only the FLRW model actually matches the observations that have been made.
A big example:
Suppose all the pieces (galaxies?) were the exact same size. You're on one of the pieces of the grenade, looking at the other ones. The nearest ones are not receding very fast, are still fairly close by and seem relatively large. (Andromeda subtends an angle 7 times wider than does the moon). The faster it is moving away from you, the further it is at the time you look at it, and the smaller it appears to you. But that's not what we see. GN-z11 is the fastest receding object from us with light reaching us after about 13.4 billion years, so it should appear the smallest (assuming they're all the same size), but it isn't. It subtends an angle far too large, as if it was less than 3 BLY distant when the light we see was emitted, not 13.4 BLY. The thing is four times too large and appears larger than similar sized things with far lower redshifts. This is exactly as the expanding space model predicts since while the light might have been emitted at c from GN-z11 back then, but the space between us and it at the time was expanding at a rate of ~6c back then, so the light actually got further away from us at first until getting to space moving ever slower until it could finally make headway against the expansion rate.
That is a very different observation than one predicted by stuff filling space from a point somewhere.
Shortly after the big bang, inflation expanded space at a rate faster than the speed of light.
Expansion is not a speed, and thus cannot be compared meaningfully with one. The units are different.
Speed is measured in km/sec, whereas expansion is measured in km/sec/mpc
We would simply need better and better telescopes to see further.
The CMB is as far as a visible-light telescope is going to see because it isn't transparent. It's like trying to see through a brick wall. Can be done, but not with binoculars.
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umm...
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mmm...
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hmmph!
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P.S. - CheerZ Everyone!
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Sure Doug, it does. Each one of us becomes the 'center' of the universe actually :)
There's a infinite amount of 'centers' to our universe and each time you move the center moves with you. We define it from a 'sphere' of light reaching earth, and so each one of us. And no matter where you or me are the magnitude shown must be the same. If it wasn't this would be wrong.
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It builds on the same principles that let us assume that the physics we have here are the physics we will meet anywhere else, and at any time. A simple proof of it is relative motion. The fact that everything moves relative something else. We get 'displaced' constantly in time and space, by earth, the solar system, our galaxy, without any of the physics we know of changing.
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Which kind of makes this little planet of ours the very centre of the observable universe doesn't it?
Thoughts?
Yes, but everywhere is the centre of the universe.
Imagine drawing dots on a balloon, and then inflating it.
All the dots move away from each other so all of them "see" themselves as the centre.
That is taking a 2 dimensional surface and projecting it onto the surface of a 3 dimensional object (sphere).
On the other hand, if you take a snow globe and shake it up, you'll have some flakes near the center of the globe, and some flakes near the surface of the globe.
Now, you might be able to project our 3 dimensional space and project it onto a 4 dimensional object. But, you would have to define what that fourth dimension was, and why it warped our view to make it look like we were in the center.
The most logical fourth dimension would be time/speed/acceleration/etc. It will take me a while to wrap my mind around that.
The corollary to @doughorrigan's question is that in any direction you look, go back the 13.8 Billion years, and you're seeing primordial events, as if they were in one place, and everywhere all at once.