Astronomy & Space Exploration

[Raoul]

i don't think we've ever been visited by aliens....but pictures like that just make it so hard for me to believe there has never been evolution of advanced life elsewhere. They may have come and gone, but I cannot look at a picture like that and think "wow we are all alone". We definitely could be a solitary freak of nature, but I'd need strong convincing.

There was a paper published at Oxford in 2018 that suggested the size of the Universe is actually 23 trillion light years, which breaks out to about 30 quintillion (30,000,000,000,000,000,000) galaxies. So yeah, tough to say we are alone, in fact, the Universe is likely full of life that we will never know about because of distance itself, plus the additional problem of the expanding Universe by way of dark energy.

 

[Raoul]

Never gets old

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[calodo2003]

Never gets old

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Looks fake every time. Props to them.

 

[Buster15]

There was a paper published at Oxford in 2018 that suggested the size of the Universe is actually 23 trillion light years, which breaks out to about 30 quintillion (30,000,000,000,000,000,000) galaxies. So yeah, tough to say we are alone, in fact, the Universe is likely full of life that we will never know about because of distance itself, plus the additional problem of the expanding Universe by way of dark energy.

And it is very likely that we will never know the true size of our Universe because we will never be able to see beyond the observable Universe.
I also believe in the Cosmic Inflation Theory which says that new Universes are constantly 'being born'. And that ours is just one of an infinite number of Universes all will differing structures and laws.

 

[Jippy]

Looks fake every time. Props to them.

That's what I was thinking. It comes in pretty quickly as well.

 

[Raoul]

Looks fake every time. Props to them.

Don't hate Calodo. If you had the work ethic to become a full time twitter troll, you too could aspire to such lofty accomplishments.

Here's a better one.

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[Volumiza]

And it is very likely that we will never know the true size of our Universe because we will never be able to see beyond the observable Universe.
I also believe in the Cosmic Inflation Theory which says that new Universes are constantly 'being born'. And that ours is just one of an infinite number of Universes all will differing structures and laws.

I also like the theory of cosmic inflation and also believe it is a seemingly constant process of birth death and regeneration of universes.

Saying that, what are your thoughts on the claim / theory of why the expansion of the universe is actually accelerating when the opposite would seem more likely?

While I can sort of get my head around infinitely large numbers when talking about the universe or universes, the literal of the term infinite or infinity is something I really struggle to believe.

 

[nimic]

I also like the theory of cosmic inflation and also believe it is a seemingly constant process of birth death and regeneration of universes.

Saying that, what are your thoughts on the claim / theory of why the expansion of the universe is actually accelerating when the opposite would seem more likely?

While I can sort of get my head around infinitely large numbers when talking about the universe or universes, the literal of the term infinite or infinity is something I really struggle to believe.

Doesn't it have to do with the ratio of dark energy to matter (dark or otherwise)? If dark energy is a property of "empty" space, as more empty space is created by the metric expansion of the Universe there is an increasing imbalance between dark energy and matter (which isn't increasing).

I seem to remember reading that.

 

[Volumiza]

Doesn't it have to do with the ratio of dark energy to matter (dark or otherwise)? If dark energy is a property of "empty" space, as more empty space is created by the metric expansion of the Universe there is an increasing imbalance between dark energy and matter (which isn't increasing).

I seem to remember reading that.

Interesting. So that suggests dark energy is or could be a by-product of cosmic expansion and not the cause?

 

[Buster15]

I also like the theory of cosmic inflation and also believe it is a seemingly constant process of birth death and regeneration of universes.

Saying that, what are your thoughts on the claim / theory of why the expansion of the universe is actually accelerating when the opposite would seem more likely?

While I can sort of get my head around infinitely large numbers when talking about the universe or universes, the literal of the term infinite or infinity is something I really struggle to believe.

I wish I was more of an expert on such things but I am very far from that I am afraid.
But my understanding of the expansion of our Universe is down to Dark Matter and Dark Energy which make up some 96% of the matter in our Universe.

I wouldn't get too hung up on the term Infinite. To my simple understanding, it just means that we don't have a number to describe something.

By the way. What was it that started up your interest in this so fascinating subject and what type of books do you read on it.

 

[Volumiza]

I wish I was more of an expert on such things but I am very far from that I am afraid.
But my understanding of the expansion of our Universe is down to Dark Matter and Dark Energy which make up some 96% of the matter in our Universe.

I wouldn't get too hung up on the term Infinite. To my simple understanding, it just means that we don't have a number to describe something.

By the way. What was it that started up your interest in this so fascinating subject and what type of books do you read on it.

I believe in the mathematical characteristic of infinity, just not the metaphysical version in terms of scale or replication.

I’m not an expert either dude but I’ve been reading and watching as much as I can for a year or so now, it’s the most fascinating and awe inspiring subject and makes our tiny and pointless squabbles down here seem embarrassing. Looking up is way more attractive and interesting than looking down and around at present.

Reading matter? I’ve only read A Breif History of time and a couple of Sean Carrol books, The Big Picture and Something deeply hidden. Mind bending / inverting stuff and if you have a vivid imagination there’s no bounds to where it can take you in terms of theorising

There’s good lectures available too, Sean Carrol, Brian Cox, Neil Degrasse Tyson etc.

Good YouTube channels include The History of the Universe and SEA.

 

[Buster15]

I believe in the mathematical characteristic of infinity, just not the metaphysical version in terms of scale or replication.

I’m not an expert either dude but I’ve been reading and watching as much as I can for a year or so now, it’s the most fascinating and awe inspiring subject and makes our tiny and pointless squabbles down here seem embarrassing. Looking up is way more attractive and interesting than looking down and around at present.

Reading matter? I’ve only read A Breif History of time and a couple of Sean Carrol books, The Big Picture and Something deeply hidden. Mind bending / inverting stuff and if you have a vivid imagination there’s no bounds to where it can take you in terms of theorising

There’s good lectures available too, Sean Carrol, Brian Cox, Neil Degrasse Tyson etc.

Good YouTube channels include The History of the Universe and SEA.

Appreciate your reply. And you make a very good point about looking up being so much better than looking down.

The 2 books I tend to rely on for reference are the 2 very good books by Brian Cox Wonders of the Solar System and Universe and Human Universe Forces of Nature.
They are very well written and, for me, relatively easy to understand.
I too have tried to understand the Stephen Hawking books but have to admit that some of it goes over my old head.

 

[Volumiza]

Appreciate your reply. And you make a very good point about looking up being so much better than looking down.

The 2 books I tend to rely on for reference are the 2 very good books by Brian Cox Wonders of the Solar System and Universe and Human Universe Forces of Nature.
They are very well written and, for me, relatively easy to understand.
I too have tried to understand the Stephen Hawking books but have to admit that some of it goes over my old head.

I said I read ABHOT, definitely didn’t understand it beyond the first third

I’ll check out those books, I like Brian Cox, obviously amazing intellect and if you like him, you may like Sean Carrol. Works on more of the quantum side of things but makes it very accessible. Certainly a very watchable guy if you catch one of his many interviews / lectures / podcasts on YouTube.

Black holes and the cosmic scale have to be my favourite areas to play around with.

 

[Buster15]

I said I read ABHOT, definitely didn’t understand it beyond the first third

I’ll check out those books, I like Brian Cox, obviously amazing intellect and if you like him, you may like Sean Carrol. Works on more of the quantum side of things but makes it very accessible. Certainly a very watchable guy if you catch one of his many interviews / lectures / podcasts on YouTube.

Black holes and the cosmic scale have to be my favourite areas to play around with.

Not heard of Sean Carrol but will certainly go by your recommendation and check him out.

 

[giggs-beckham]

Doesn't it have to do with the ratio of dark energy to matter (dark or otherwise)? If dark energy is a property of "empty" space, as more empty space is created by the metric expansion of the Universe there is an increasing imbalance between dark energy and matter (which isn't increasing).

I seem to remember reading that.

Yes the dark energy density remains constant so as the universe expands the amount of dark energy increases proportionally.

 

[Revan]

Interesting. So that suggests dark energy is or could be a by-product of cosmic expansion and not the cause?

Dark energy is essentially the cosmological constant in Einstein’s theory of relativity. A nonzero positive constant, so with every unit of space there is some associated dark energy that expands the space. The more space, the more dark energy, the faster universe expands and thus more space, then more dark energy and so on.

It might also be that there is no such thing as dark energy and Einstein’s theory needs a total rewriting but I think scientists think that is less likely.

 

[Volumiza]

Dark energy is essentially the cosmological constant in Einstein’s theory of relativity. A nonzero positive constant, so with every unit of space there is some associated dark energy that expands the space. The more space, the more dark energy, the faster universe expands and thus more space, then more dark energy and so on.

It might also be that there is no such thing as dark energy and Einstein’s theory needs a total rewriting but I think scientists think that is less likely.

Yeah I get the fundamental theory of why we think DE is present and also where DE helps Einsteins cosmological constant, which I kind of like but have been also trying to read more about another theory called K-essense.

I suppose I was hooking onto the more space = more dark matter / energy as opposed to more space but with the existing amount of DE stretched over it. The former would imply something is, or could be creating more, the latter could suggest that space or the universe itself is finite.

Just the most interesting sh*t.

 

[Buster15]

Dark energy is essentially the cosmological constant in Einstein’s theory of relativity. A nonzero positive constant, so with every unit of space there is some associated dark energy that expands the space. The more space, the more dark energy, the faster universe expands and thus more space, then more dark energy and so on.

It might also be that there is no such thing as dark energy and Einstein’s theory needs a total rewriting but I think scientists think that is less likely.

If Dark Energy really is a form of energy and the more space, the more DE, then if DE is increasing, does it not then follow that the increasing DE must be coming from another source of energy??
Or have I got this completely wrong.

 

[Revan]

If Dark Energy really is a form of energy and the more space, the more DE, then if DE is increasing, does it not then follow that the increasing DE must be coming from another source of energy??
Or have I got this completely wrong.

No idea if the conversation of energy holds for dark energy, it probably should be (I also was never to understand how related, if any, it is to the inflaton field. Another interpretation is to consider gravity as negative energy, albeit at this stage I have no idea what I am talking about). I think two ways of thinking about it is a) cosmological constant so just a constant of universe that makes it expand, b) some type of cost/loss function for the space. A property of it is that it is completely uniform, so at any m2 in the universe, you have the same amount of it. You might have also heard about it as the vacuum energy. This is way beyond my payscale but from what I have read they are the same thing but one comes from GR while the other from QM.

It’s biggest implication is that eventually the universe will be only dark energy. The more dark energy, the more space gets generated, the more space, the more place for dark energy to be created, so more dark energy. At some stage, all galaxies will be forever far from each other, and at some stage, all particles are gonna be forever far from each other. A sad ending for the universe.

Not heard of Sean Carrol but will certainly go by your recommendation and check him out.

Sean Carroll is a quite good physicist who also tries to make physic accessible for everyone. He did during the pandemic a YouTube series called ‘the biggest ideas in the universe’ which was pretty interesting, has a podcast, and wrote a couple of books for people who want to know more about physic but are not physicists (‘something deeply hidden’ is for many- world interpretation of QM, while ‘the particle at the end of universe’ is about the Higgs boson). He has a relativity book too, and unlike most of science popularizers (like Tyson DeGray, Michio Kaku nowadays) is actually working in the field.

 

[Buster15]

No idea if the conversation of energy holds for dark energy, it probably should be (I also was never to understand how related, if any, it is to the inflaton field. Another interpretation is to consider gravity as negative energy, albeit at this stage I have no idea what I am talking about). I think two ways of thinking about it is a) cosmological constant so just a constant of universe that makes it expand, b) some type of cost/loss function for the space. A property of it is that it is completely uniform, so at any m2 in the universe, you have the same amount of it. You might have also heard about it as the vacuum energy. This is way beyond my payscale but from what I have read they are the same thing but one comes from GR while the other from QM.

It’s biggest implication is that eventually the universe will be only dark energy. The more dark energy, the more space gets generated, the more space, the more place for dark energy to be created, so more dark energy. At some stage, all galaxies will be forever far from each other, and at some stage, all particles are gonna be forever far from each other. A sad ending for the universe.


Sean Carroll is a quite good physicist who also tries to make physic accessible for everyone. He did during the pandemic a YouTube series called ‘the biggest ideas in the universe’ which was pretty interesting, has a podcast, and wrote a couple of books for people who want to know more about physic but are not physicists (‘something deeply hidden’ is for many- world interpretation of QM, while ‘the particle at the end of universe’ is about the Higgs boson). He has a relativity book too, and unlike most of science popularizers (like Tyson DeGray, Michio Kaku nowadays) is actually working in the field.

Thank you yet again for your interesting thoughts. I do love the way you are so honest about things you say you don't understand. Which is so refreshing.
So many people pretend that they understand certain things but in reality just don't.

Like so many things related to this thread, DE and DM are so fascinating, mainly because scientists simply don't know much about them yet. At school, it was drummed into us about energy conservation. And I do understand that at any point in time, you will have the same amount of energy even though it can be in different forms.

I do think that Hubble discovery that our Universe is actually expanding is still the most significant scientific discovery. Because it fundamentally changed our way of thinking about our Universe.

 

[Invictus]

If Dark Energy really is a form of energy and the more space, the more DE, then if DE is increasing, does it not then follow that the increasing DE must be coming from another source of energy??
Or have I got this completely wrong.

• We should conceive dark energy, quintessence et cetera as a spectrum of possibilities (e.g. in the Standard and ΛCDM Model dark energy is the convenient cosmological constant Λ) for stuff that is missing, and cannot be irrefutably derived or explained (like precise mechanisms for cosmic expansion) by the current theories and mathematical capabilities and cosmic understanding of the human species (or indeed direct observations over the foreseeable future, as measurement is supposed to collapse quantum waves).
• We should do away with the term expansion, it transmits the wrong ideas on a conceptual level. If space-time is a piece of cloth, it's not being stretched and expanded — instead, newly created threads are being woven into the fabric and there's symmetry breaking. A universe where new space-time is created does not have to follow time-translation symmetry or Poincaré's symmetry of Special Relativity in an all-encompassing sense, so the law of conservation of energy can be disregarded when you consider the totality (though it is assumed that conservation of energy applies locally). There's no “another source of energy”, it's spontaneously created or added (according to certain models).
• Reference: https://www.newscientist.com/people/emmy-noether/, https://courses.physics.ucsd.edu/2010/Fall/physics200a/LECTURES/CH07.pdf
• One possible easy-to-explain model for dark energy (which is mostly consistent with observations, as far as we know, for now) can be expressed thusly, as a cosmic chicken-and-egg situation: think of it as an intrinsic property of the space-time itself, an energy density constant for all intents and purposes. For 1m³ of space-time you have a certain energy density and a certain total energy. As new space-time is woven out of thin air in all places in all directions (though this isn't a straight-line law and the Hubble Constant (i.e., relative rate of expansion) is not actually a constant as it does not follow time-translation symmetry either ***), you have the same energy density in 1m³ (assumption of local conservation of energy, for now) but a higher overall energy (in relation to the starting energy of just 1m³). And so on and so forth.
• Closely tied to the aforementioned model and Big Bang cosmology, you have this sequence/evolution: era dominated by radiation → era dominated by matter → era dominated by dark energy (assumed to be the instigator of the final era, the inescapable death knell, thought to have started when the universe was 9.5-10 billion years old (ironically, this is roughly when the Solar System was formed according to our estimates)).

*** Eventually, in the very far future, with the assumption that the universe's energy density remains constant, dark energy will practically be all that remains, and the Hubble Constant will become an actual fundamental physical constant too (asymptotically approaching a value of about 56.8 km/s/Mpc).

 

[Buster15]

• We should conceive dark energy, quintessence et cetera as a spectrum of possibilities (e.g. in the Standard and ΛCDM Model dark energy is the convenient cosmological constant Λ) for stuff that is missing, and cannot be irrefutably derived or explained (like precise mechanisms for cosmic expansion) by the current theories and mathematical capabilities and cosmic understanding of the human species (or indeed direct observations over the foreseeable future, as measurement is supposed to collapse quantum waves).
• We should do away with the term expansion, it transmits the wrong ideas on a conceptual level. If space-time is a piece of cloth, it's not being stretched and expanded — instead, newly created threads are being woven into the fabric and there's symmetry breaking. A universe where new space-time is created does not have to follow time-translation symmetry or Poincaré's symmetry of Special Relativity in an all-encompassing sense, so the law of conservation of energy can be disregarded when you consider the totality (though it is assumed that conservation of energy applies locally). There's no “another source of energy”, it's spontaneously created or added (according to certain models).
• Reference: https://www.newscientist.com/people/emmy-noether/, https://courses.physics.ucsd.edu/2010/Fall/physics200a/LECTURES/CH07.pdf
• One possible easy-to-explain model for dark energy (which is mostly consistent with observations, as far as we know, for now) can be expressed thusly, as a cosmic chicken-and-egg situation: think of it as an intrinsic property of the space-time itself, an energy density constant for all intents and purposes. For 1m³ of space-time you have a certain energy density and a certain total energy. As new space-time is woven out of thin air in all places in all directions (though this isn't a straight-line law and the Hubble Constant (i.e., relative rate of expansion) is not actually a constant as it does not follow time-translation symmetry either ***), you have the same energy density in 1m³ (assumption of local conservation of energy, for now) but a higher overall energy (in relation to the starting energy of just 1m³). And so on and so forth.
• Closely tied to the aforementioned model and Big Bang cosmology, you have this sequence/evolution: era dominated by radiation → era dominated by matter → era dominated by dark energy (assumed to be the instigator of the final era, the inescapable death knell, thought to have started when the universe was 9.5-10 billion years old (ironically, this is roughly when the Solar System was formed according to our estimates)).

*** Eventually, in the very far future, with the assumption that the universe's energy density remains constant, dark energy will practically be all that remains, and the Hubble Constant will become an actual fundamental physical constant too (asymptotically approaching a value of about 56.8 km/s/Mpc).

Wow. I have read and tried my best to understand this. But it just highlights to me how little I understand about this complex subject.
And it highlights to me how much more knowledgeable others are.
Thank you for this.

 

[giggs-beckham]

Dark energy is essentially the cosmological constant in Einstein’s theory of relativity. A nonzero positive constant, so with every unit of space there is some associated dark energy that expands the space. The more space, the more dark energy, the faster universe expands and thus more space, then more dark energy and so on.

It might also be that there is no such thing as dark energy and Einstein’s theory needs a total rewriting but I think scientists think that is less likely.

Why would GR need a complete rewrite if DE doesn't exist?

 

[Murder on Zidanes Floor]

Wow. I have read and tried my best to understand this. But it just highlights to me how little I understand about this complex subject.
And it highlights to me how much more knowledgeable others are.
Thank you for this.

Really, seemed really rudimentary to me.nope

 

[nimic]

• We should conceive dark energy, quintessence et cetera as a spectrum of possibilities (e.g. in the Standard and ΛCDM Model dark energy is the convenient cosmological constant Λ) for stuff that is missing, and cannot be irrefutably derived or explained (like precise mechanisms for cosmic expansion) by the current theories and mathematical capabilities and cosmic understanding of the human species (or indeed direct observations over the foreseeable future, as measurement is supposed to collapse quantum waves).
• We should do away with the term expansion, it transmits the wrong ideas on a conceptual level. If space-time is a piece of cloth, it's not being stretched and expanded — instead, newly created threads are being woven into the fabric and there's symmetry breaking. A universe where new space-time is created does not have to follow time-translation symmetry or Poincaré's symmetry of Special Relativity in an all-encompassing sense, so the law of conservation of energy can be disregarded when you consider the totality (though it is assumed that conservation of energy applies locally). There's no “another source of energy”, it's spontaneously created or added (according to certain models).
• Reference: https://www.newscientist.com/people/emmy-noether/, https://courses.physics.ucsd.edu/2010/Fall/physics200a/LECTURES/CH07.pdf
• One possible easy-to-explain model for dark energy (which is mostly consistent with observations, as far as we know, for now) can be expressed thusly, as a cosmic chicken-and-egg situation: think of it as an intrinsic property of the space-time itself, an energy density constant for all intents and purposes. For 1m³ of space-time you have a certain energy density and a certain total energy. As new space-time is woven out of thin air in all places in all directions (though this isn't a straight-line law and the Hubble Constant (i.e., relative rate of expansion) is not actually a constant as it does not follow time-translation symmetry either ***), you have the same energy density in 1m³ (assumption of local conservation of energy, for now) but a higher overall energy (in relation to the starting energy of just 1m³). And so on and so forth.
• Closely tied to the aforementioned model and Big Bang cosmology, you have this sequence/evolution: era dominated by radiation → era dominated by matter → era dominated by dark energy (assumed to be the instigator of the final era, the inescapable death knell, thought to have started when the universe was 9.5-10 billion years old (ironically, this is roughly when the Solar System was formed according to our estimates)).

*** Eventually, in the very far future, with the assumption that the universe's energy density remains constant, dark energy will practically be all that remains, and the Hubble Constant will become an actual fundamental physical constant too (asymptotically approaching a value of about 56.8 km/s/Mpc).

Is the "approaching a value of about 56.8 km/s/Mpc" also the reason why the current consensus seems to be the Heat death (no more potential energy), as opposed to the Big Rip (the acceleration increasing and eventually ripping everything apart from everything else) - and definitely not the Big Crunch (gravity reasserting control and everything going back into a point)? Or am I conflating concepts here? I admit I don't understand why it would be 56.8, I thought the Hubble constant was 70 km/s/Mpc.

 

[Invictus]

Is the "approaching a value of about 55.8 km/s/Mpc" also the reason why the current consensus seems to be the Heat death (no more potential energy), as opposed to the Big Rip (the acceleration increasing and eventually ripping everything apart from everything else) - and definitely not the Big Crunch (gravity reasserting control and everything going back into a point)? Or am I conflating concepts here? I admit I don't understand why it would be 56.8, I thought the Hubble constant was 70 km/s/Mpc.

The Hubble Parameter (H) varies with time, and with it the Hubble Constant (H₀). The Hubble Constant is just the Hubble Parameter for a given frame of reference (e.g. the Hubble Constant one billion years ago was equal to the Hubble Parameter of that particular point in time (higher than right now, as it is directly proportional to the density of matter in the system), the Hubble Constant in the current frame of reference is equal to the Hubble Parameter in the current frame of reference, in a billion years the Hubble Constant will be equal to the Hubble Parameter of that particular point in time (lower than right now)).

You can look at it is this: Hubble Parameter = √((8πG/3)*ρ) + (Λc²/3 ΩΛ))

*** G = Gravitational Constant, ρ = density of matter, Λ = cosmological constant, c = speed of light (also a constant), ΩΛ = omega lambda sub.
*** the equation also has a subtraction for curvature and scale factors, but that bit can be disregarded because k = 0 in a universe that will become as perfectly flat as possible.
*** In the universe of the far future, ρ (i.e., density of matter in the system) will approach 0 for all intents and purposes.

So you will ultimately have H = √(Λc²/3 ΩΛ)), and if you solve further with estimated ΩΛ values (assuming the cosmological constant and speed of light hold), H will proportionally arrive at roughly √2/3 of the H right now (which is 70 km/s/Mpc, yes). And with that change in the Hubble Parameter (H), you will have a consequent change in the Hubble Constant (H₀).

The Heat Death thing includes everything from universal to remote scales, yes? In a broader sense, the projected development of things being pushed much further away from each other (the Hubble Constant is obviously relevant here) plays a significant role, but in a local sense you also need thermodynamic equilibrium with the dissipation of free energy (which will take very, very, very, very, very long (and life in particular could survive around ultramassive or supermassive black holes until they've disappeared via radiation and loss of angular momentum)).

 

[Buster15]

https://www.bbc.co.uk/news/science-environment-66066710

The European Space Agency is launching the Euclid space telescope aimed at mapping the Universe from some 10bn years ago in other to attempt to identify Dark Energy and Dark Matter.

 

[calodo2003]

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[Buster15]

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Yes I have read about this.
It was not that long ago that we were being told that space was completely empty and a vacuum with nothing there at all.

 

[Cheimoon]

Early Universe seems to run at 20% speed

Researchers have spotted the earliest instance of cosmological time dilation, which makes time seem to run at one-fifth of today’s speed in the early Universe — a phenomenon explained by the general theory of relativity. Observing a quasar hailing from a time when the Universe was just one-tenth of its current age is “like watching a movie with the speed turned down”, says astrophysicist and study leader Geraint Lewis. Quasars are supermassive black holes surrounded by an extremely bright disc of hot gas and are among the oldest objects in the Universe. Previous observation of time dilation made using distant supernovae went back to only around half the age of the Universe, when time seemed to run at 60% of today’s speed.

Article from the Guardian: Astronomers observe time dilation in early universe | Space | The Guardian
Scientific paper: Detection of the cosmological time dilation of high-redshift quasars | Nature Astronomy

 

[entropy]

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https://www.removepaywall.com/article/current

 

[WPMUFC]

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https://www.removepaywall.com/article/current

 

[Invictus]

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Scientific American link.

 

[Counterfactual]

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Scientific American link.

So, Freese (with colleagues) proposed in 2008 that dark stars may exist, and now she says these images may be dark stars but may also just be very old ordinary galaxies?

"The researchers can’t yet prove that the objects are dark stars—only that their characteristics are consistent with being either dark stars or galaxies populated by regular fusion-powered stars."

Well, then.

 

[giggs-beckham]

Article from the Guardian: Astronomers observe time dilation in early universe | Space | The Guardian
Scientific paper: Detection of the cosmological time dilation of high-redshift quasars | Nature Astronomy

I can't understand this. I thought the expansion of the universe creates more space-time rather than stretches space-time.

 

[nimic]

I can't understand this. I thought the expansion of the universe creates more space-time rather than stretches space-time.

The stretching they're talking about is the stretching of light, i.e. redshift (or blueshift, but that's not really relevant here). I'm no astronomer, but basically what the researchers found was that the light from certain very distant objects (quasars) was redshifted as predicted, something which up until now had not been conclusively shown. Any change in an object with very high redshift will to us appear slower than normal, and the higher the redshift the slower the change.

I'm struggling to explain this, someone competent help me out.

 

[Shakesy]

The stretching they're talking about is the stretching of light, i.e. redshift (or blueshift, but that's not really relevant here). I'm no astronomer, but basically what the researchers found was that the light from certain very distant objects (quasars) was redshifted as predicted, something which up until now had not been conclusively shown. Any change in an object with very high redshift will to us appear slower than normal, and the higher the redshift the slower the change.

I'm struggling to explain this, someone competent help me out.

When we talk about the universe expanding, we're referring to the observation that galaxies are moving away from each other over time. This isn't because galaxies are physically moving through space (though they do have some motion of their own), but rather because the very fabric of space itself is expanding.

To get a sense of what this means, imagine a loaf of raisin bread dough before and after you let it rise. If you put raisins in the dough and then let it rise, the raisins will move away from each other as the dough expands. The raisins themselves aren't moving through the dough, instead, new dough is appearing between them, pushing them apart. This is similar to what happens in the expanding universe. The galaxies are like the raisins, and space is like the dough.

In reality it's obviously a bit more complex than this

 

[nimic]

When we talk about the universe expanding, we're referring to the observation that galaxies are moving away from each other over time. This isn't because galaxies are physically moving through space (though they do have some motion of their own), but rather because the very fabric of space itself is expanding.

To get a sense of what this means, imagine a loaf of raisin bread dough before and after you let it rise. If you put raisins in the dough and then let it rise, the raisins will move away from each other as the dough expands. The raisins themselves aren't moving through the dough, instead, new dough is appearing between them, pushing them apart. This is similar to what happens in the expanding universe. The galaxies are like the raisins, and space is like the dough.

In reality it's obviously a bit more complex than this

Is this an explanation to me or to giggs-beckham? I see now my phrasing at the end theren might have been a bit confusing.

 

[giggs-beckham]

I know all of what you guys said in terms of red shift (JWST being developed to be able to look at the most distant light etc) and the matter in the universe not moving etc. But I'm not sure that the fabric of space itself is stretching as in dark energy density remains constant etc.
I don't see how GR comes into play with the expansion of the universe.
Moving at different relative velocities and being near a gravitational field will dihalate time in relative frames of reference. Haven't heard of this effect due to the expansion of the universe. Will research tomorrow.

 

[giggs-beckham]

When we talk about the universe expanding, we're referring to the observation that galaxies are moving away from each other over time. This isn't because galaxies are physically moving through space (though they do have some motion of their own), but rather because the very fabric of space itself is expanding.

To get a sense of what this means, imagine a loaf of raisin bread dough before and after you let it rise. If you put raisins in the dough and then let it rise, the raisins will move away from each other as the dough expands. The raisins themselves aren't moving through the dough, instead, new dough is appearing between them, pushing them apart. This is similar to what happens in the expanding universe. The galaxies are like the raisins, and space is like the dough.

In reality it's obviously a bit more complex than this

Also your analogy is saying more bread is being created between the raisins. So it isn't stretching as the density remains constant.
Imagine if you will a balloon half blown up with dots all over. Now blow up the balloon to full, the dots don't move but the balloon expands and stretches.
Is it bread or a balloon