Astronomers discover supervoid 1.8 billion light years across

[gary]

Hannah Devlin in the April 21st 2015 edition of The Guardian reports on a paper published
in the Monthly Notices of the Royal Astronomical Society entitled
"Detection of a supervoid aligned with the cold spot of the cosmic microwave background".

See http://www.theguardian.com/science/2015/apr/20/astronomers-discover-largest-known-structure-in-the-universe-is-a-big-hole

See http://mnras.oxfordjournals.org/content/450/1/288

[Eratosthenes]

This is an interesting observation which matches the Cosmic Background radiation maps. I wonder if the researchers used the map as a guide when searching the night sky, or did they discover this low density void in space and then made the reference to the CBR map?

The visible size of the Universe is currently estimated at about 92 billion light years - just to place this 1.8billion LY supervoid in perspective

[xelasnave]

How many voids have been observed.
I recall of another half billion lights theses which was not Bootes Void, so maybe that's a starting count of three including the super void.
Void seems a most inappropriate word.
Void to me suggests empty. Less dense is hardley a void.
I have wondered about their dark matter content..could there be more dark matter or less.
I could suggest support for either however I wonder what observations will show.
I wonder if voids are expanding or collapsing.

[Eratosthenes]

Physicists have already measured that the so called "vacuum" of space isn't really devoid or energy or matter. It exerts a pressure, and is measurable. Quantum particle pairs emerging from nothing, and then combining to completely vanish back into where they came from is a very spooky thought.

Perhaps the term void doesn't make sense in any context whatsoever unless it is stated what the volume of devoid of.

I agree with you though, I would have referred to this region of space as sparse or even a dessert rather than a super void. (and if it turns out that 3/4 of the Universe is indeed comprised of Dark Energy, which cannot be detected directly, then what does this term "super void" really mean?":shrug:

[sjastro]

As the article states a "void" is a region where there is less mass or energy than its surroundings. The void is manifested as a cold spot on the cosmic radiation background.

The cold spot mechanism has a somewhat subtle connection to the slowing down of clocks in gravitational wells as exemplified by the GPS time corrections of satellite clocks to keep them synchronized with Earth clocks.

A clock located on the Earth's surface runs slower than a clock on an orbiting satellite. This is a result of gravitational time dilation as the Earth's clock sits deeper in the gravitational well than the satellite's clock.
Similarly a photon located deep in a well is gravitationally blue shifted when compared to a photon higher up the well It has more energy the deeper it is in the well. A photon moving up the well gains gravitational potential energy and loses kinetic energy, the situation is reversed moving down the well.

If the void is at non cosmological scales, the CMB photons would behave as if they were in the Earth's gravitational well.
A photon entering the void will gain gravitational potential energy but lose kinetic energy, on exiting the void kinetic energy is gained but gravitational potential energy lost. Since this is symmetrical there is net loss or gain in energy and there is no change to the CMB relative to the observer.

If the void is as cosmological scales (very very big) the void will stretch out as space expands. It means the energy density decreases as space expands and well as the energy difference between the void and the surrounding region. Since photons occupy the void at time scales long enough for the void to expand, photons entering the void lose more kinetic energy then gaining the energy when exiting it.

As a result CMB photons are more red shifted which appears as a cold spot on the CMB relative to the observer.

Steven

[Eratosthenes]

sjastro,

these variations in the cosmic background radiation, as measured today in an expanding universe were once quantum fluctuations

great avatar btw, Eulers formula is one freaky formula involving the number 1, zero, pi, e and the imaginary number i. absolutely sublime equation. Says something about mathematics, or logic. Does it say anything about reality though?

[sjastro]

Peter,

Quantum fluctuations are small scale effects and apply to the Universe when it was small enough to behave as a quantum mechanical system.
This occurred at a Planck time of 10^-43 second or less.
Unfortunately there is no Unified Theory to link General Relativity to Quantum mechanics at these scales, hence our understanding of the Universe at the Planck time is very limited.

The CMB as we observe it was formed around 300,000 years after the Big Bang.

The variations in the CMB after subtracting out dipole effects such as the motion of our galaxy relative to the CMB, are caused by the following factors.

(1) Polarization of scattered CMB photons caused by minute temperature variations in the plasma forming the CMB.
(2) Polarization due to Inflation.
(3) Polarization of photons due to gravitation lensing caused by intervening matter between the CMB and observer.
(4) The Sunyaev-Zel'Dovich effect where CMB photons gain energy by being scattered by the intervening matter.
(5) The mechanism as described in this thread which is known as the Integrated Sache Wolfe effect.



The use of complex numbers "in reality" is common.
Electrical Engineers for example know all about them.

I find it intriguing how the term pi crops up in so many theories in physics.

Regards

Steven

[xelasnave]

Hi Peter thank you for your input.
You mention the pressure of space and I must tell you this is a matter that I was somewhat preoccupied years ago. I considered the Pioneer anomaly could be explained if this pressure could be properly quantified. Also that gravity was related.
Anyway years ago my point however it's something I find very interesting.

Hi Steven
Thank you for your input.
You really have a knack for explaining complicated matters such that they are clear to a non professional.
Mmmm the reality question maybe we need a thread like at cosmo quest.

[Eratosthenes]

sjastro,

the quantum fluctuations and perturbations were "blown out" during the inflation and expansion period. The variation in density, both with respect to baryonic matter and energy, we observe today are a reflection of the initial fluctuations. In fact it is argued that the trigger for the Big bang is a consequence of quantum instability or fluctuations. What was the nature of the initial singularity that the Big Bang sprouted from? Was is "ideally" perfect? In that case why would it become unstable and trigger a big bang?

Although the Big bang theory isnt settled yet with various cosmological models operating in the Physics market place, the fluctuations in the initial conditions seem to be providing remnants/artifacts on a large scale for Astronomers to observe today. Of course they could be just that - artifacts of our lack of understanding or equipment limitations etc. Who knows.

Some argue (like Einstein throughout his life) that quantum mechanics, although very accurate and validated by experimentation and measurement, is a Stochastic model of the atomic (and cosmic) world, and a deterministic model may yet be discovered by science. On the other hand, it may prove to be impossible to describe the atomic world with a deterministic model. Who knows?

My gut feeling is that every "scale" science has delineated for convenience or necessity is intimately linked and intertwined in some fundamental way. Finding the linkages or a global model of some kind may well be beyond human endeavors (or just around the corner)

Who knows?:shrug:

(and yes, the imaginary number system is very useful in many fields of science and engineering, including electrical engineering as you state. But the square root of negative 1 is undefined by definition, it "exists" (not exists) on an "imaginary" (real) number line as do i^3, i^5, i^7....i^odd integer. But i^2, i^4, i^6....i^even is fine by me)

[Eratosthenes]

....have you looked into quantum vacuum fluctuations of the electromagnetic field? (The Casimir effect, describes the quantum vacuum as NOT empty but containing virtual particles that are continually fluctuating or in a state of flux. This manifests itself as a force which Casimir measured using the famous two plate experiment in a vacuum)

Its an interesting area of Physics, which kind of dispels the notion that you can have a perfect "NOTHING" state where there is literally and absolutely NOTHING in existence (matter or energy).

who knows?:shrug:

[xelasnave]

Consider this.
Say we have as absolute void, no galaxies not even a single atom.
Say the void has a dia of one billion light years.
At a point in the centre (any point really) we can say there infinite tradgectori and each will observe something passing thru.
When I try to imagine such a nothing I can't fit everything in..imagination but it suggest to me that the complexity of the quantum world will be difficult.
I think GR is so special because somehow it works to describe what may be going on in nothing.
Re particles popping in and out...I thought that was a math thing where realty is seen differently.
I recall a thread by math folk on a forum which left me thinking such.

[xelasnave]

Please excuse poor spelling I am a poor speller but it's this correct thing.

[xelasnave]

I wonder how two plates in such a nothing would act?

[xelasnave]

Or two spheres..
Sorry Steven

[sjastro]

Peter,

We seem to be discussing two separate issues here.
I'm referring to the variations in the structure of the CMB not the Universe itself.
The only mechanism that may relate to quantum fluctuations affecting the CMB is B mode polarization of photons due to inflation. This effect however is very subtle compared to the other mechanisms I have mentioned.

In fact the investigation of B-mode polarization in the CMB due to inflation is one of the more embarrassing cases for mainstream science.
It's "discovery" was announced by the BICEP2 team last year and was hailed as one of the greatest recent scientific discoveries rivalling the Higgs boson.
Unfortunately the researchers underestimated the amount of magnetized dust in our own galaxy that produces a similar photon polarization.
The mistake was realised after the Planck probe revealed its data.

So at this stage we have no direct evidence of the CMB being affected by quantum fluctuations.




There are "Theories of Everything" ranging from String theory to Loop and Quantum gravity theories that incorporate GR into Quantum mechanics in "various degrees". Then there are more direct applications of GR into Quantum mechanics pioneered by Stephen Hawking and are generally referred to as Quantum Field Theory in curved space time.

Some aspects of String Theory do not appear to be falsifiable, other such as Quantum gravity are mathematical nightmares that are overwhelmed by infinities when one attempts to calculate the quantum state changes.

The theories are a starting point in a unified field theory.
These theories do make predictions which can either support or sink the theory. For example Hawking's theory predicts that Black Holes can evaporate.



Since simple complex numbers can be represented as a coordinate on an X-Y graph there is nothing terribly unreal about imaginary part of the number when they are interpreted geometrically.
They can be used in vector analysis.

A simple example is a target shooter. On a windless day the shooter aims directly at the target and shoots with a muzzle velocity which is a real number.
If there is a strong cross wind the shooter aims left or right of the target.
In this case the velocity is represented by a complex number and is the vector sum of the cross wind velocity which is an imaginary number and the velocity when shooting directly at the target which is a real number.

Regards

Steven

[Eratosthenes]

there is a connection between the two

[sjastro]

Alex,

Let's take your experiment but make some modifications.
Let's suppose there are two plates or spheres.

The space between the plates or spheres is absolutely empty of mass, a "vacuum" where we impose the condition that not even particle/antiparticle pairs can pop into and out of existence.

If we use the Newtonian version of gravity, the gravitational field only exists due to the presence of mass.

The GR version of gravity is radically different. Not only is the mass a source of gravity but gravitational field itself is a source of gravity.
It has been referred to as "the gravity of gravity."

Since the field is a source of gravity it carries gravitational energy and since the fields extend into the space between the masses there can never be true void or vacuum.

The same applies to the cosmological scale voids in the Universe. These regions carry gravitational energy but the energy content of these regions is far less energy than its surrounds.

If your want learn more about the differences between Newtonian and GR gravity here is an excellent intro that doesn't get bogged down in the maths.

http://www.einstein-online.info/spotlights/gravity_of_gravity

Steven

[Eratosthenes]

well apparently a force is measured known as the Casimir effect. The initial experiments conducted by Casimir and his co-worker predicted a net attractive force between the plates, when all other factors were taken into consideration,.

Its a very difficult experiment to carry out. It requires two pates which are perfectly parallel, perfect conductors (which dont exist) and a perfect vacuum (which also doesnt exist.)

I believe that most of the experimental results had large error bars when compared with the theory. But eventually in the 1950s experiments were repeated with about 5% accuracy and fitted the theoretical predictions very well.

Its an interesting experiment, based on Quantum theory, which predicts that virtual particles should be spontaneously and randomly emerging and then anhialating one another before vanishing again. This should produce a measurable effect in the Lab.

[xelasnave]

Thank you Steven
I look forward to the link.

[xelasnave]

Peter I should have acknowledged my knowledge of Casimir effect.

[xelasnave]

Steven very helpful link thank you.
It's getting a second read.

[Eratosthenes]

Have you read the OP in a new thread in this section on NASA's new electrodynamic drive which apparently operates in a vacuum? The researcher offered an explanation that is based upon the quantum vacuum - ie virtual particles.

[xelasnave]

Peter I have not but I will.