The Universe is slowly dying of slow death, according to an international team of scientists who measured the energy produced by 200 000 galaxies and discovered that it was two times less than that generated there are two billion years. ---- http://www.icrar.org/news/news_items/media-releases/the-universe-is-dying2
Astronomy / Space The universe is slowly dying
- Thread starter Patrick_68000
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Which always makes me wonder where the energy came from in the first place.
If inflation is correct (which I'd put good money on, but not my life savings) - then in a sense it comes from the collapse of the inflaton field - a process known as reheating. https://en.wikipedia.org/wiki/Inflation_(cosmology)#Reheating
More generally, to comment on the original article: it's not exactly surprising news as the press release itself notes, but it's certainly a fantastic and comprehensive survey of this that's been done.
Am I bothered?
Yes.
The law of conservation of energy bothers me here. The universe was created with a certain amount of energy, so the theory goes. The law applies to isolated systems of which the observable Universe is one example. So, to paraphrase Amigacooke, is the Universe part of another system where the energy given to the Universe on creation was taken from?
I have a headache.
Yes.
The law of conservation of energy bothers me here. The universe was created with a certain amount of energy, so the theory goes. The law applies to isolated systems of which the observable Universe is one example. So, to paraphrase Amigacooke, is the Universe part of another system where the energy given to the Universe on creation was taken from?
I have a headache.
Conservation of energy is a funny thing in general relativity. In particular the inflaton field (and present day dark energy, if both are things at all) superficially look like energy isn't conserved. They stay at constant density no matter what volume you put them in.
Normally if you have a piston of gas for example, and you push on that piston you compress that gas. You think that the amount of matter in that gas has stayed the same (and being in a smaller volume its density has gone up) but if you think about it you had to push on that piston to compress the gas, and the energy you expended to do that has gone into the gas, so the amount of matter has gone up in a way (E=mc2 and all that) and the density is a little bit higher than you expect. With something like the inflaton field, it has a negative rather than positive pressure and rather than you doing work to compress it, you get energy out for compressing it. And the amount you get out is such that the density stays the same. Equally if you expanded the volume it had you'd have to do work and it again would keep the same density.
Now an immediately obvious tricky issue is that if you put something like that throughout the universe and make the universe bigger, it's not clear what is doing the work to keep the density the same - there's no outside wall to push or pull against. So there isn't really anything, but it does still keep the same density as the universe expands. So you have an expanding universe with a field like that in and it gets bigger and the total amount of stuff in it has gone up. And then you turn all that weird stuff into ordinary matter and energy and suddenly you've got a whole load of it...
So what's going on with the conservation of energy? Well one way to look at it is through Noether's theorem. Noether figured out that if you can express a symmetry about the universe (so that something looks the same when viewed from a different perspective) you can calculate an associated quantity that is conserved. In this case, the conservation of energy is in a sense a result of the fact that the laws of physics don't change with time. They'll be the same tomorrow as today, and were the same yesterday. The equivalent for the laws of physics being the same over there as over here gives you conservation of momentum. Unfortunately, the universe is actually a dynamic place and space and time are not fixed, so the background the laws of physics are supposed to be working in are changing. This means energy isn't conserved, or at best that you have to rethink how you're going to calculate it in order to keep it conserved.
So you can either take the view that energy isn't actually conserved, or you can take the view that the energy has been accounted for by some other balancing of the books elsewhere (bundling it under the name of gravitational energy), and figuring out how that's done and if it can be done is not trivial, and it's perhaps not going to lead you to any significantly better understanding. Which is unfortunate, and indeed having a headache is probably the most appropriate response to the situation even if it's not the most productive.
A few links: http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
http://preposterousuniverse.blogspot.co.uk/2004/05/energy-and-intelligence.html
Quite.
Though no- doubt we will probably be treated to a round of blaming our modern lifestyle for killing the universe, using up all its energy on our quest for greed.
Err, yeah, OK.
But your cylinder / piston of gas can be seen as an isolated system. You applying energy from an external system, so the isolated system is now the cylinder / piston of gas and the system from which the energy applied to the cylinder / piston came from. If we are considering just the piston / cylinder then we have, by definition, an adiabatic process. If someone was in the cylinder pulling the piston to compress the gas then we still have an isolated system.
Does the Universe, seen as a system, lose energy to its surroundings? If so, then we have inferred that the Universe cannot be seen as an isolated system for the purpose of the law of conservation of energy.
I've lost energy to go on.
Well exactly. That's what I meant by "Now an immediately obvious tricky issue is that if you put something like that throughout the universe and make the universe bigger, it's not clear what is doing the work to keep the density the same - there's no outside wall to push or pull against."
In a sense, the conservation of energy as a law happens to be a property of a lot of other 'laws' of physics. It happens not to be a particularly clear cut property of general relativity though. It's either the case that it doesn't hold, or you need to count gravitational energy as the source of the extra energy you need if you can define it well enough.
To say I understand general relativity would be a lie.
The CoE may be a 'property' but it seems it is also a constraint on other 'laws' of physics. If a 'law' of physics can theoretically invalidate the CoE then it must be suspect as a 'law' or axiom. The CoE is an axiom of physics is it not? From which or on which other laws depend on to be seen as 'laws'.
Saying the CoE is a property of general relativity confuses me. But that is not a clearly defined one seems to me that it is not well understood.
I see the gravitational energy as the person in the cylinder.
Where is the centre of mass of the Universe? It must be on the move.
Does the Universe lose gravitational energy to its surroundings?
I must now wash the pots!
I think it's sensible to start from the idea that the conservation of energy is a direct result of time symmetry - that the laws of physics should be the same at all points in time. This is probably a sensible property for anything called a law of course! The problem then is that general relativity makes understanding that and translating it into something that can be calculated nontrivial, just by the nature of the theory as not just operating in some background space and time but defining it and how the background can change. It's messy, and sometimes I feel it's quicker and leads to a better understanding to say that sometimes that CoE just doesn't apply.
I think it's fair to say that without some other understanding of the universe (e.g. brane theories) the universe doesn't have surroundings, as it is everything!
I don't want to think people can go off and violate CoE on a whim - it does apply here on Earth and in a local sense, but we're not the universe as a whole and an awful lot of stuff gets hard to nail down in that kind of universe-scale sense.
I think it's fair to say that without some other understanding of the universe (e.g. brane theories) the universe doesn't have surroundings, as it is everything!
I don't want to think people can go off and violate CoE on a whim - it does apply here on Earth and in a local sense, but we're not the universe as a whole and an awful lot of stuff gets hard to nail down in that kind of universe-scale sense.
You can imagine the last few civilisation in a sea of utter blackness, huddling around the final few stars still active, knowing their time is ticking down...
And they have just one choice... how long do they risk waiting until they set off the device they've built to create another singularity and create another big bang to kick start the whole process again. Just like the civilisations did the last time around...
This makes cold in the back ...
Time is irrelevant.
What appears to begin and end is all one and the same. Life and death are partners, twins, identical. What once was, always is.
Our meager human observation of the evolution of time is a construct. An application of our own innate conceptions of a Universe beyond our comprehension.
Or some crap like that.
What appears to begin and end is all one and the same. Life and death are partners, twins, identical. What once was, always is.
Our meager human observation of the evolution of time is a construct. An application of our own innate conceptions of a Universe beyond our comprehension.
Or some crap like that.
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I'm sure as you're lying there, breathing away your last few breaths... It maybe won't seem that time is quite so irrelevant...
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The truth is, most of what is claimed to be known is not known at all. It's essentially dogma.
Someone posed the point, where did the energy come from and the notion of parallel universes was suggested. Yet there is absolutely no evidence for these parallel universes.
The theroising of the universe is so fraught with missing bits, preposterous notions and self serving dismissal as to call into question how much is actually known.
The reality, very little. Sadly, our scientricians seem more keen on impressing us that admiting.
Oh, I wasn't speaking from a human perspective. Perhaps an observation from an inter-dimensional being. No, my human affinity for time is quite strong. Which is why I hope to die by bus accident.I'm sure as you're lying there, breathing away your last few breaths... It maybe won't seem that time is quite so irrelvant...
EDIT: Ok, thought a minute before saying this...but oh well
The concept of the irrelevance of time is more of a spiritual construct for me. It is how I dealt with the deaths of some of my friends and family and it is how I deal with the thought of my own death. Others choose a deity who will save them from the eternal sleep, whereas I prefer to see myself as one tiny solution to a grand energy equation that has no beginning or end. Totally made up, I know, but as a long time Catholic turned atheist, I needed something. Just like I still go to church, although it is Humanist a "church", for the community gathering part of it, I maintain a spirituality, so to speak, that keeps me from staring into that deep despair.
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We're on a similar page there then. Not being religious, its tricky to rationalise your own mortality, and come to terms that the norm is a Universe without you in it.
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