They say energy and matter are the same thing - completely interchangeable.
I know Dark Energy is quite a mystery at the moment, but it seems to me Dark Energy does not contribute to matter production. Probably on the contrary, I don’t know.
Dark Energy contributes to space production though. It causes space to expand. Dark Energy does not seem to equate with matter. It will not foster new matter or new matter structures. Plus, the existing matter will eventually get ripped apart due to the accelerated expansion of the universe caused by Dark Energy.
Is this what the universe seems to be like now? Is this what proponents of the Heat Death version of the distant future have in mind?
Does Dark Energy create hollower and hollower space as the universe plunges into the Big Freeze?
It doesn’t exactly “create” anything. Space doesn’t expand via the introduction of new space. It’s just the existing space gets stretched.
The football field still only has 100 yards. The yards are just a teense longer than they were. There isn’t any new 101st yard.
ETA: space, however, will get “hollower” – or less dense with matter – because matter, either atoms or galaxies, doesn’t expand the same way space does. Gravitational attraction is stronger than the pressure of expansion. (And as for the atom, the electrical force is even vastly stronger yet.) So the average distance between galaxies is increasing.
The answer is we don’t really know and we’re not even sure of the broad nature (i.e. equation of state) of dark energy. The prevailing view on the broad nature of dark energy is that it probably takes the form of a cosmological constant, as this is arguably its simplest form and the best fit for the evidence, though other possibilities like quintessence or even more extreme forms such as phantom energy have not been ruled out.
If dark energy is a cosmological constant, there are several, not necessarily inequivalent ways to describe it, some of which also apply (with some or no modification) to other forms of dark energy. The main three are:
a) The natural curvature of spacetime, this is a classical way of describing it. Einstein when he formulated general relativity first assumed that empty spacetime, in the absence of any gravitational field, is flat, but the simplest modification to GR is to do away with this assumption and just assume a constant scalar curvature determined by a physical constant, i.e. the cosmological constant. Ironically Einsetin was the first (I believe) to make this modification to create his failed steady-state cosmological model.
b) Vacuum energy, a more quantum way of looking at it. Vacuum energy has the same broad characteristics (i.e. equation of state) as the cosmological constant, which means that on a relevant scale they would be indistinguishable. However this leads to the famous “worst prediction of theoretical physics” as the vacuum energy predicted by quantum electrodynamics is many orders of magnitude larger than the observed cosmological constant. Despite this jarring disagreement though there may still be a deep underlying link with dark energy and the vacuum energy of quantum fields due to yet unknown cancellations.
c) As a fluid, which is a way of describing it that slots in easily with the classical and the quantum, as real classical fluids have an underlying quantum nature. Dark energy has a nature that is unlike any classical form of mass-energy we observe gravitationally (e.g. radiation, normal matter, dark matter) in that it has a repulsive effect due its strong negative pressure, but that doesn’t preclude it from being a result of an unknown quantum field, which in turn would have an associated particle.
Only space between objects expands, with no local consequences.
Therefore, the universe works as an infinite collection of clusters of matter separated by an ever-expanding vacuum. Does space expansion actually mean vacuum expansion in practical terms?
Dark energy may be an intrinsic property of existence, of vacuum energy, of spacetime – I for one can only grope here. But this infinite and accelerated expansion of space may reveal something strange about space itself.
There is a relationship between matter and space curvature. A flat spacetime will contain nothing, but this rapport is unidirectional. Therefore, there may be nothing within a curved space.
The Newtonian view allowed for an independent space grid. Nowadays we’re taught space is strictly linked to the existence of matter created through the Big Bang, which has always made me feel the end of the universe will practically lead to the end of space.
But in the far future of the universe, when stars have burned out and black holes have evaporated, expansion will have stretched everything to incomprehensible dimensions and the universe will be an incredibly thin soup of protons. Double that time, to allow protons to vanish as well (if you are to take the Big Freeze to its final consequences), and you’ll be left with the enormous empty carapace of space, which may contain nothing but still be curved.
Thus, not only can space exist independently but it might also be the only thing left when the universe is gone. Like the fossilized shell of an extinct nautilus.
First of all, mass and energy are not completely equivalent. Mass is one component of energy, but only one component: There is energy that is not mass. And in any closed system, the portion of energy that is mass is constant and cannot be changed. The only reason that it appears that it can be changed (so-called conversion of matter to energy, or vice-versa) is that people often deal with non-closed systems, or assume that the masses of all of the subsystems add up to the mass of the total system.
Second, dark energy is, so far as we can tell, energy. It follows all of the same rules as any form of energy, including the rules concerning mass. All that’s odd about it is its pressure, which is both extremely large (unusual, but not unprecedented) and negative (which is more extraordinary).
Of note, its gravitational effects are also, so far as we can tell, completely ordinary. If you take the known laws of gravity (as determined from study of relatively ordinary substances), and apply those laws to a substance with extremely large negative pressure, then you get the repulsion that everyone talks about with dark energy. It is the physical properties of the substance that are unusual, not gravity itself.
At least, all of this is the case if one regards dark energy as a substance. It’s mathematically equivalent to describe it as being a property of gravity itself, without invoking any sort of independently-existing substance. The substance explanation is in vogue right now, but with current models and technology, there’s really no way to tell the difference.
I will confess to being quite befuddled about thinking of it as a substance. Sticking a constant into a PDE and seeing space-time change I can get my head around, but how can a substance stretch space? In what manner does it gain traction (for want of a more useful metaphor) on space-time itself.
Substance seems to imply something that has location, maybe density, moves etc etc. A ubiquitous substance seems otherwise just another luminiferous aether.
72% of the universe contents is Dark Energy. It is increasing in time and it will eventually near 100% of all there is.
In the meantime the universe will double in size every 10 billion years or so.
I know I’ve said that already but I’m perplexed at the amount of space created during the final process of matter destruction and evaporation as the universe plunges into the dark death of the Big Freeze, leaving an incredibly large empty shell behind.
And personally, I, too, prefer to think of it as being a property of gravity, rather than as a separate substance, but as I said, the two views are (to the best of our ability to tell) interchangeable.
