
Why the Tiny Weight of Empty Space Is Such a Mystery - digital55
https://www.quantamagazine.org/why-the-dark-energy-problem-spawned-the-multiverse-hypothesis-20180312/
======
Veelox
Question, if assuming a multiverse to explain the exactness of the
cosmological constant is a defensible position, is there any reason not to
consider the deist view and say the universe was created with the cosmological
constant needed for life to form as an equally likely outcome?

~~~
lisper
> is there any reason not to consider the deist view

No reason not to consider it, but the evidence against it is overwhelming.
Specifically, the evidence is overwhelming that whatever the ultimate cause
is, it is computationally simple, that is, its Kolmogorov complexity is small.
That is fundamentally at odds with most people's conception of God.

~~~
dvt
> Specifically, the evidence is overwhelming that whatever the ultimate cause
> is, it is computationally simple, that is, its Kolmogorov complexity is
> small. That is fundamentally at odds with most people's conception of God.

The probability that the first cause (FC) is computable is basically zero, so
it most likely won't have a Kolmogorov complexity. For example, not even
entropy is computable[1][2], let alone FC.

[1] [https://arxiv.org/pdf/0808.1678.pdf](https://arxiv.org/pdf/0808.1678.pdf)

[2]
[https://www.math.iupui.edu/~mmisiure/open/JM1.pdf](https://www.math.iupui.edu/~mmisiure/open/JM1.pdf)

~~~
lisper
I think that when you talk about the "first cause" you mean something
different than what I mean when I say "ultimate cause." I'm not talking about
what caused the Big Bang, I'm talking about what causes physics _now_.

It is of course possible that whatever caused the big bang was computationally
complex. There is no way to eliminate that possibility. But if it was, it left
no evidence behind.

------
joe_the_user
The argument for multiple-worlds seems to be that if you take the most elegant
possible formulation of the "equations of the universe", you find that some of
constants in these equation have to be set to apparently arbitrary values to
imply a universe like our own.

This seems to rest on an assumption that simple patterns tend to continue
beyond our immediate perception, like if a person see a part of a sphere
sticking out of the sand on a beach, they would tend to expect an entire
sphere to buried beneath.

The two questions that appear would: is formulation really the simplest and
does this kind of reasoning apply "outside the universe", given the universe
is all that we use to make such judgments.

~~~
abakker
I am probably wrong, but I've always liked the (fictional, in my head)
solution that black holes are these "buried spheres" and that all the problems
we have with dark matter and energy are really result of black holes
"draining" mass from one "world" to another. In my Sci-fi mind, the big bang
is what comes out the other side of a black hole, so, when a black hole forms,
it starts draining matter and energy from one universe into another.

Essentially, we'd never be able to see all the mass our theories predict,
because we'd never be able to observe all the linked worlds/universes past the
event horizons.

~~~
r00fus
So the universe is not a closed system?

~~~
creep
Maybe not! Some people think the universe is shaped like a torus, and that
everything in the universe, all of the energy flow, all of the minute systems,
also reflect this. If that were the case as well, it may make sense to say
that the universe is not a closed system. This universe would be a toroidal
aspect of a larger toroidal universe and so on. And perhaps in the middle of
that torus, you would see energy merging to a singularity.

Obviously I'm not claiming any of this as fact. But it is interesting to think
about. After a certain point there is non fact-based validity in applying
philosophy to our conception of universes.

~~~
pault
This is more or less the model of the universe in the Culture books by Iain M
Banks.

~~~
r00fus
Which book was that described in? I have read only a few of Banks' books
(preferred Surface Detail, though The Player of Games was excellent)

~~~
pault
I believe it is mentioned in passing in several of the books, but if I recall
correctly the Hydrogen Sonata and Excession went into more detail. He does
discuss it in his notes on the culture[0]:

> We accept that the three dimensions of space we live in are curved, that
> space-time describes a hypersphere, just as the two dimensions of length and
> width on the surface of a totally smooth planet curve in a third dimension
> to produce a three-dimensional sphere. In the Culture stories, the idea is
> that - when you imagine the hypersphere which is our expanding universe -
> rather than thinking of a growing hollow sphere (like a inflating beach-
> ball, for example), think of an onion.

> An expanding onion, certainly, but an onion, nevertheless. Within our
> universe, our hypersphere, there are whole layers of younger, smaller
> hyperspheres. And we are not the very outer-most skin of that expanding
> onion, either; there are older, larger universes beyond ours, too. Between
> each universe there is something called the Energy Grid (I said this was all
> fake); I have no idea what this is, but it's what the Culture starships run
> on. And of course, if you could get through the Energy Grid, to a younger
> universe, and then repeat the process... now we really are talking about
> immortality. (This is why there are two types of hyperspace mentioned in the
> stories; infraspace within our hypersphere, and ultraspace without.)

> Now comes the difficult bit; switch to seven dimensions and even our four
> dimensional universe can be described as a circle. So forget about the
> onion; think of a doughnut. A doughnut with only a very tiny hole in the
> middle. That hole is the Cosmic Centre, the singularity, the great
> initiating fireball, the place the universes come from; and it didn't exist
> just in the instant our universe came into being; it exists all the time,
> and it's exploding all the time, like some Cosmic car engine, producing
> universes like exhaust smoke.

> As each universe comes into being, detonating and spreading and expanding,
> it - or rather the single circle we are using to describe it - goes
> gradually up the inner slope of our doughnut, like a widening ripple from a
> stone flung in a pond. It goes over the top of the doughnut, reaches its
> furthest extent on the outside edge of the doughnut, and then starts the
> long, contracting, collapsing journey back in towards the Cosmic Centre
> again, to be reborn...

> Or at least it does if it's on that doughnut; the doughnut is itself hollow,
> filled with smaller ones where the universes don't live so long. And there
> are larger ones outside it, where the universes live longer, and maybe there
> are universes that aren't on doughnuts at all, and never fall back in, and
> just dissipate out into... some form of meta-space? Where fragments of them
> are captured eventually by the attraction of another doughnut, and fall in
> towards its Cosmic Centre with the debris of lots of other dissipated
> universes, to be reborn as something quite different again? Who knows. (I
> know it's all nonsense, but you've got to admit it's impressive nonsense.
> And like I said at the start, none of it exists anyway, does it?)

[0]:
[http://www.vavatch.co.uk/books/banks/cultnote.htm](http://www.vavatch.co.uk/books/banks/cultnote.htm)

------
klank
> Force fields have positive zero-point energies while matter fields have
> negative ones

This tidbit stuck out to me. Anybody able to offer a deeper explanation of
why?

~~~
cammikebrown
That's an explanation proposed for why we can barely measure any gravity
stemming from the huge energy contained in the zero-point field. The idea is
that the fermion field (matter) and the boson field (energy) cancel each other
out. This theory is part of supersymmetry.

~~~
auntienomen
This answer is slightly misleading. Fermionic fields have negative vacuum
energy, while bosonic ones have positive. This is an basic fact of quantum
field theory, a consequence of Lorentz invariance and Fermi-Dirac statistics
(resp. Bose-Einstein statistics).

Supersymmetry makes use of this fact: When the bosons and fermions come in
pairs, their vacuum energies can cancel because they have opposite sign. But
the association of minus signs to fermions and plus signs to bosons is older
and more elementary than supersymmetry.

~~~
auntienomen
I wish I had an elementary conceptual explanation for why this association
exists. It's a simple calculation, but hard to describe without resorting to
equations. Maybe the best I can say is that when one writes down the energy
function for a quantum mechanical system of many particles, it has a form
which is _strongly_ constrained by special relativity. The variables which
describe the creation of particles are perfectly paired with the variables
which describe the annihilation of particles. For bosons, these variables
commute, just like ordinary functions. For fermions, these variables anti-
commute, picking up a sign when you exchange them. If you repeatedly exchange
these variables to rewrite energy function as vacuum energy + energy of 1
particle + energy of 2 particles + ...., you discover that the fermions
contribute negatively to the vacuum energy while bosons contribute positively.

~~~
klank
Thanks. This is what I was looking for when I originally posed the question.

So, if I understood you correctly, the restriction of Lorentz symmetry on the
Hamiltonian in turn requires QFT creation and annihilation operators to
commute/anticommute (the anticommute part what then ultimately drives a
negative energy contribution from fermionic fields when summing over all
possible energy states).

What causes the anticommute properties? Is there a non-abelian symmetry group
backing fermion fields somewhere?

~~~
auntienomen
That's about right. There's a tiny bit of confusion

The anticommutation of fermions is a consequence (the content, really) of the
spin-statistics theorem, which is a consequence of Lorentz invariance &
unitarity.

------
chmike
The Space Time Quantization theory of Prof. Auguste Meessen [1] leads to an
explanation of the accelerating expansion of the universe, the cosmological
constant suggested by Einstein (drak energy) and dark matter. It uses just
simple and basic physics. The only new hypothesis leading to this theory is
that measured distances would be quantified. That means that there would be a
minimal measurable length.

[1]
[http://www.scirp.org/journal/Articles.aspx?searchCode=August...](http://www.scirp.org/journal/Articles.aspx?searchCode=Auguste++Meessen&searchField=authors_complete&page=1&SKID=0)

------
hateful
This is totally based on zero evidence, but it seems to me, as a casual
observer, that maybe there are elementary particles whizzing aren't detectable
until they combine with other elementary whizzing particles and combine to
make the detectable ones? So like hydrogen can be fused into helium (I know,
easier said than done!), sometimes the they collide and create a detectable
particle. This explains the Casimir effect in that there really wasn't nothing
between the plates, just the stuff whizzing through the plates that we can't
block.

~~~
comboy
AFAIK the only particles that appear out of nowhere (which would in your view
happen when those non-detectable particles collide) are particle-antiparticle
pairs[1]. It does explain the Casimir effect.

1\.
[https://en.wikipedia.org/wiki/Quantum_fluctuation](https://en.wikipedia.org/wiki/Quantum_fluctuation)

------
woodandsteel
I really like this article. I have read a lot of articles that bandy about
terms like dark energy, the cosmological constant, and the multiverse. This
was the first thing I have read that clearly explains how they link together.

However, I have a question. The article says that dark energy "presence causes
the cosmos to expand ever more quickly, since, as it expands, new space forms,
and the total amount of repulsive energy in the cosmos increases" But wouldn't
this violate the first law of thermodynamics?

~~~
tzs
This post on Steve Carroll's blog [1], called "Energy Is Not Conserved",
answers that question fairly clearly.

[1]
[http://www.preposterousuniverse.com/blog/2010/02/22/energy-i...](http://www.preposterousuniverse.com/blog/2010/02/22/energy-
is-not-conserved/)

~~~
woodandsteel
Thank you, that link answers my question.

------
thriftwy
There are a lot of states of vacuum. Our space is either in rock bottom stable
state or in metastable one.

Maybe it's just the state in which this energy is as small as it gets?

~~~
pixl97
At least we hope so

[https://en.wikipedia.org/wiki/False_vacuum#Vacuum_metastabil...](https://en.wikipedia.org/wiki/False_vacuum#Vacuum_metastability_event)

------
crb002
Would relativity explain a lot of it? "Empty" space isn't always empty. You
put a camera anywhere in the known universe and almost instantly it will get
bombarded by particles.

All those particles in flight, albeit sparse, have mass or in the case of
photons can collide turning their energy into mass.

TLDR. What is the mass of all in flight particles?

~~~
matte_black
No, even empty space, where there is not even one particle or even the thought
of anything aspiring to be a particle within the defined area, will have a
tiny weight.

~~~
wodenokoto
But don't particles and anti-particles form everywhere constantly? Won't they
add a temporary weight, before cancel out?

------
ythn
> This fine-tuned situation suggests that there might be a huge number of
> universes, all with different doses of vacuum energy, and that we happen to
> inhabit an extraordinarily low-energy universe because we couldn’t possibly
> find ourselves anywhere else.

At a certain point "God" is going to be a simpler explanation than "infinite
universes with infinite cosmological constant variance", etc.

~~~
bufferoverflow
"God" is not an explanation. You're "answering" a mystery with an even bigger
mystery.

Explaining lightning with Zeus instead of electricity just raises more
questions.

~~~
ythn
Neither is "multiverse". That's just as untestable and unverifyable and
mysterious as God.

~~~
bufferoverflow
We don't know if either hypothesis is testable. Multiverse is not as
mysterious as "god did it" (a.k.a magic), it's a very specific hypothesis.

You can "explain" absolutely anything with god/magic, and many religious
people do. Try that with multiverse. It doesn't work.

~~~
dragonwriter
> Multiverse is not as mysterious as "god did it" (a.k.a magic), it's a very
> specific hypothesis.

If you can test the existence of another “universe”, it's really the same
universe.

Plus, even if you have a model of a multiverse in which the component
universes have variation on particular axes, you can still ask why you have
such a well-constructed set of parameters such that varying them will allow
life somewhere on the multiverse. Multiverse is not only a non-terrible
hypothesis, it's one that doesn't do anything but kick the problem it is meant
to explain one step further down the road without transforming it's general
shape.

~~~
dragonwriter
> Multiverse is not only a non-terrible hypothesis,

Missed the edit window, but non- _testable_ , not non- _terrible_.

