[ExI] Dark energy = (anti)gravity?
Stuart LaForge
avant at sollegro.com
Sat Nov 4 05:47:41 UTC 2017
John Clark wrote:
> On Sat, Oct 14, 2017 Stuart LaForge <avant at sollegro.com> wrote:
>> Thermodynamics says that entropy is a function of state. That means it
>> is path independent so it doesn't matter how the universe got into its
>> initial state of zero entropy because all paths, including reversible
>> ones, are equally valid.
>
> ?All paths leading up to the first instant of time are equally invalid
> because there were none. ?
How do you know that? Feynmann famously hypothesized that antimatter was
matter was matter going backwards in time. If equal amounts of matter and
antimatter were created at the "beginning" of time, then maybe the reason
we see so little antimatter in our universe is that it became its own
universe that blossomed on the backside of the "big bang". So there might
not have been a beginning of time, but instead, an *origin* of time where
t=0 such that positive and negative time run in the two opposite
directions.
>> But in the case of the universe, all those stop watches started at the
>> same time and in the same place.
>
> ?But to measure a time interval both a start and stop point is needed and
> all those stopwatches stopped at different times because ?there is no
> universal agreement on simultaneity, so there is no agreement on if watch
> X stopped
> before watch Y or watch Y stopped before watch X.
Ah but there is a universal agreement on simultaneity - a precise
mathematical definition given by special relativity in fact. It is the
3-dimensional space-like hyperplane passing through the observer's origin.
All events equidistant from the observer that lie in the hyperplane will
occur simultaneously with those happening closer to the observer observed
sooner.
So when you want to know what another observer that is moving relative to
you thinks is simultaneous, you can just apply the Lorentz tranformations
and you get the result that the plane of simultaneity "tilts" toward the
direction of motion as the relative speed approaches c.
In fact from the stationary observer's POV all events that are
simultaneous for the moving observer will lie on the hyperplane t =
(v/c^2)*x in the stationary observer's coordinate system.
> And to make things even
> worse the stopwatches are running at different rates. So there is no
> universal agreement on when the Big Bang happened; right here right now
> we say it was 13.8 billion years ago, but others would disagree
Under the assumption that we are the stationary observer, then our
measurement of 13.8 billion years is the maximum observable age of the
universe and all the moving observers will measure a younger universe
whose clock is moving slower than theirs.
Of course, we can't actually be stationary relative to the big bang
because at the very least we are moving away from it in time. This
suggests the universe could be far older than we measure it to be.
Furthermore the universe as whole is significantly larger than the
observable part of it, then there are parts of the universe for which our
"big bang" has not yet happened.
This why I think in terms of what I call causal cells rather than multiple
universes in a multiverse because causal cells do not require more than
four dimensions and instead gradually and continuously overlap one another
across infinite space-time.
The more you think about it, the less consistent big bang cosmology becomes.
> There are a infinite number of ways a bunch of distant clocks can be
> brought ?together in a expanding universe, and I don't see how everyone
> could agree on how to do it. Should distant clock X be brought to clock Y
> or should clock Y be brought to clock X? It makes a difference because
> one clock would be accelerated and the other clock would not and a
> accelerated clock runs slower than one in a inertial frame of reference.
Why would you bring the clocks back together again? Just read the distant
clocks through a telescope and adjust for relative velocity and distance.
This of course limits you to the clocks in the your causal cell but
bringing clocks together physically is even more limited.
> A universe can be flat and still be
> ?expanding and even ?
> accelerating if there is a property of space itself that causes it to
> ?intrinsically ?
> contain energy, and we found out 20 years ago that there is, about 1/100
> of a ?n?
> erg per cubic meter. A erg is about as much energy as a common housefly
> needs to perform one push-up so that may not sound like much but there is
> a awful lot of otherwise empty cubic meters out there, so much so that
> today dark energy makes up 70% of the mass/energy in the entire universe.
That is one way to look at it. It might even be mathematically equivalent.
The way I am hypothesizing it happens is that everything we can see is
inside a hollow sphere of infinite thickness and constant density and thus
infinite mass. And so everything in the sphere is being gravitationally
pulled to the closest part of the sphere because the infinite mass of the
universe is just a little closer in that direction.
Thus causing negative pressure or tension in the outward radial direction
and the appearence of gravitational repulsion. Of course, one could always
look at it geometrically, in which case there is simply an inflection
point of curved spacetime where the curvature changes direction.
> And
> that percentage will increase as time passes because both normal matter
> and dark matter will keep getting diluted but dark energy will not, the
> more space ?that space itself creates
> the more dark energy there is ?,?
> but the amount of matter ?in the universe ?
> will be constant.
Why would you insist that matter be conserved but that energy is not?
Both Hawking radiation and radioactive decay are adding particles to the
universe. Those new particles then engage one or more pre-existing
particles using one or more of the four fundamental forces producing a
range of potential and kinetic energies and thus new masses.
While it would seem at first glance that fusion decreases the particle
number of the universe, when one considers photons and neutrinos as
particles, it is clear that fusion too increases the particle number of
the universe.
So if the number of particles is increasing and they have relative
velocities and therefore kinetic energy, it is clear that the mass of the
universe must be increasing. But if energy is conserved, then that new
mass is cancelled by the negative energy of curved space-time caused by
gravity and the total energy of the universe stays at zero or perhaps a
non-zero constant. The point is, energy is conserved.
Obviously, as the particle number and volume of the universe increases, so
too will the entropy. Since those particles will have more degrees of
freedom available to them.
>> And the philosophical benefits of an infinite universe are also
>> satisfying. It would mean that we too are infinite with countless copies
>> repeated through time and space across the cosmos. Countless versions of
>> us living identical lives. Countless versions of us living every possible
>> permutation of our lives. Infinite copies of us taking every possible
>> road, almost all of which are unique.
> ?I find that philosophically satisfying too, and maybe its true but the
> universe is under no obligation to conform to human desires. ?
But it does conform to physical laws that make human desires possible at
least here and now.
> ?The only reason humans invented conservation laws is to help us
> understand how the world works. If in circumstances far from everyday life
> we have to contort them in complex ways so they still apply then there
> gets to be a point where it's not worth the effort.
It is not the conservation laws that are the contortions but the
cosmological constant, dark energy and dark matter. They are like
epicycles. No need to make the universe more complicated than it already
is.
> The important thing is
> we can use the ? ?
> mathematical reasoning ? ?
> in Noether's theorem ? to conclude that if the fundamental laws that tell
> objects ?how to move do not change with the passage of time then energy is
> conceived, but General Relativity says they do
> change with the passage of time.
But GR is itself a law that allows one to determine the laws of motion in
any particlular time and place. So those local laws are highly
deterministic and consisten in the "there and then".
> I go back to my example of a gamma ray
> photon produced in the Big Bang, because something very fundamental has
> changes since that photon was produced, space has expanded, that gamma ray
> photon is now a far less energetic microwave photon and eventually space
> will have expanded so much it will be a radio photon with a wavelength ? ?
> longer than the observable universe and be undetectable even in principle.
> The energy in that photon would have been conserved if space didn't
> expand, but it does so it isn't. ?
My equations admittedly do not allow one to "itemize" the energy content
of space-time into components. I need tensors and GR for that. But with GR
one often loses sight of the forest for the trees. I have intentionally
simplified the picture by combining all the components of energy into a
single gravitational mass density.
Your photon is losing energy to the negative energy of the expansion of
curved spacetime just like gravity. Except that the curve is in the
opposite direction due to the influence of infinite mass strewn across
infinite spacetime the same as if the photon was climing a hill with a
crater atop it representing your local gravity well.
If the gravity well was deep enough and you were in it, then the
gravitaional blue-shift to the photon would recover the energy it lost to
the expansion of the universe and energy would be conserved. What the
negative energy of the universe takes, it can give back, in the right time
and place.
>> keep in mind that in a flat universe Dc is not just the critical ? ?
>> density of the universe but also the actual density of the universe. ?
>
> The equation you're using, Dc = 3H^2/(8*pi*G)
> ,
> ?where Dc is the critical density ?
> is only valid if the cosmological constant is zero, but we've known for 20
> years that i ?t?
> can't be zero because the universe is accelerating. So density alone
> doesn't determine geometry of the universe and ?thus we can't be living
> in a ? simple?
> ?
> Friedmann universe
The acceleration of the universe is just the curvature of spacetime in the
outward direction caused by the mass density in all the other causal
cells. Come on, acceleration, curvature, and gravity are all synonomous.
It's just the equivalence principle and Einstein came up with that. Not
me.
> ?The density of normal matter and Dark Matter has decreased over time but
> it has become clear that the gravitation caused by matter alone (not
> even with the help of dark Matter) is insufficient to explain the
> evolution of the universe. For a very long time the expansion of the
> universe was slowing down just as you'd expect, but about 5 billion years
> ago (and nearly 9 billion year after the Big Bang) the deceleration
> stopped and things started to accelerate. This can only be because the
> matter became diluted and so did the gravitational force trying to slow
> things down but some property of space itself called Dark Energy which
> nobody understands causes things to speed up, so whatever it is when there
> is more space there is more Dark Energy ?
Where is the evidence that the universe has been decreasing in density? If
space-time is expanding and the particle number of the universe is
increasing, then density could be going up.
>> Good. That's all my theory needs is for gravity to be able to "influence
>> things" faster than light. No Shannon entropy need be exchanged.
>
> ?But you also said:?
>
> ?*"?*
> *In a flat? universe, dark energy is just superluminal gravity at long
> ranges* ?"?
>
> ?I'm not sure what that means. If Dark Energy is a property of space
> itself as if seems to be then it doesn't need to travel a long distance to
> be manifest. ?
Gravity only "travels" if you think of time and space seperately, the same
intituitive way that you perceive them. If you simply think in terms of
geometric spacetime, then nothing is actually moving FTL or otherwise
except your perceptions.
Another way of describing superluminal gravity is by saying that the slope
of spacetime can become infinite and at a certain point, it can become so
steep that not even light can escape it. The point is, event horizons,
both gravitional and cosmological are the "walls" of the causal cells we
observers reside in. And gravity can pierce right through those walls in
all directions.
>
>> My earlier attempts at quantum gravity have been overturned by the
>> super-long Compton wavelength of the graviton reported by LIGO.
>
>
> ?I don't know what you mean by that, LIGO has not detected the graviton
> nor has anybody else, it is purely theoretical and may not even exist and
> even if it does I think its unlikely anyone will be able to find one this
> century. ?
They did not detect the graviton, they simply used their data to bound its
mass and Compton wavelength, if it exists.
>From their earlier paper:
"Finally, assuming a modified dispersion relation for gravitational waves
[97], our observations constrain the Compton wavelength of the graviton to
be λg > 10^13 km, which could be interpreted as a bound on the graviton
mass
mg < 1.2×10^−22 eV/c^2."
>From paragraph 6 of the discussion
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102#fulltext
>> My equations simply lump pressure and tension together with matter
>> density and radiation density through the mass-energy equivalence
>> principle. It just deals with total density of all components of the
>> stress-energy tensor converted to mass.
>>
>
> Both pressure and tension are potential energy, but Einstein says
> pressure causes gravitational attraction but ?tension (negative pressure)
> causes gravitational repulsion.
Gravity is just spacetime curvature and spacetime can curve toward or away
from a mass. What I am saying is that spacetime cannot curve away from a
mass without curving toward some other mass somewhere.
What's outside of our light-cone? Literally almost *everything*.
Stuart LaForge
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