Wednesday, January 29, 2014

A moment of silence replaces the big bang

Shhh.

“Big Bang” has become a household expression, but for physicists it’s primarily a Big Headache. Exactly what happened in the first moments of our universe is still not understood. In this early phase, when matter densities were extremely high, quantum fluctuations of space and time were large. We know that much, but we still do not know to describe these fluctuations which would require a quantum theory of gravity. Without that, we cannot reliably tell what banged, if anything.

It is generally expected that quantum gravity will remove the Big Bang singularity that general relativity predicts was the origin of our universe, but we don’t know with what it will be replaced. However, while we do not yet have a full theory of quantum gravity, different models for the early universe have been investigated. These are models based on, but not strictly speaking derived from, theoretical approaches to quantum gravity. The best known of these models are string cosmology and loop quantum cosmology, based on string theory and loop quantum gravity respectively.

Loop quantum cosmology in particular is well known for replacing the Big Bang with a “Big Bounce”: When the density of matter reaches a certain critical density (related to the Planck scale) contraction turns back into expansion. For a recent status update on string cosmology, see here.

A completely different approach to quantum gravity that we discussed recently is Causal Dynamical Triangulation which avoids singularities by discretizing space and time into chunks of finite size. In this approach it was recently found that space-time can exist in different phases, much like water exists in different phases. In the early universe, temperatures were high, and space-time might have been in a different phase, one in which space-time falls apart into causally disconnected pieces.

Phase diagram of space-time in CDT. See earlier post for details

It is thus very interesting that a similar behavior was recently found in loop quantum cosmology, an approach which a priori doesn’t have anything to do with Causal Dynamical Triangulation.

Jakub Mielczarek argues that the modification that arises through a loop-quantization of space-time can be rewritten in a suggestively simply way, as a density-dependence of the speed of light. A brief summary are these conference proceedings:

    J. Mielczarek,
    Asymptotic silence in loop quantum cosmology
    AIP Conf. Proc. 1514 (2012) 81, [arXiv:1212.3527].

The full length paper is here. It’s very technical, but the main conclusion is this: The higher the density, the slower the speed of light. At half the critical density, the speed of light reaches zero – this means points become causally disconnected. But things become even more interesting when the density becomes larger than half the critical density and increases towards the critical density. In this range the speed of light becomes an imaginary number and its square becomes negative. This means that time stops existing and turns into space. Physicists say space-time becomes Euclidean.

This finding realizes the so-called “no-boundary” proposal by Hartle and Hawking, and it also matches well with even earlier, quite general, considerations of what should happen nearby a singularity. In the classical theory, the causal disconnect happens only asymptotically and was dubbed ‘asymptotic silence’. In the quantized case, the causal disconnect happens at a finite time and replaces the singularity, and thus the big bang, by a singularity free region, a “moment of silence.”

I find this an intriguing development because here we have several different routes that point towards the same behavior at high density, much like is the case with dimensional reduction. I will not be surprised if further theoretical support for the moment of silence appears in the soon future. The big question is of course if traces of this silent beginning of the universe are left in observables like structure formation or the cosmic microwave background.

21 comments:

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Bee,

If proved true this doesn't seem to bode well for Smolin's time is real hypothesis if space-time becomes simply space. Also I'm wondering if this has implications regarding the non localness of some aspects of reality as fundamentally stemming from this phase of its existence and thereafter subtly affecting its after bounce evolution. Perhaps as the Tremolos once expressed in song silence is golden after all.


“After silence, that which comes nearest to expressing the inexpressible is music.”

-Aldous Huxley

Best,

Phil

kashyap vasavada said...

Hi Bee: I hear that there is a big problem in understanding how such a hot fireball start with a very low entropy. Does any of these models address this puzzle?

L. Edgar Otto said...

It seems we are asked to solve nature's smoking gun cover up of singularity by suggesting we should follow the information.
One would think these new considerations bring us closer to.understanding gravity, but I find it even more mysterious and outside the scope of our books.
Who ages in the twin paradox but the one undergoing acceleration?
perhaps there is nothing but an event horizon-firewall thus like a brane all is existing in this Flatland of paradox. All is at that place where space is interchanged with time as if only there is an atmosphere.
Half infinity makes sense. Two entangled photons equal at half light speed each or one virtual the other the c of acceleration. Energy as half the universe as visible, half of potential infinity.
I understand the clear arguement of this post. But could we not accomidate the chirality ideas and particle triplication of particle generations that we have such levels as "big bounces" and not just one?

johnduffieldblog said...

Bee: IMHO the density-dependent speed of light is good. That's essentially the coordinate speed of light varying in a gravitational field. And the expanding universe can be likened to pulling away from a "frozen star" black hole. Good stuff. What's not to like? But IMHO time stops existing and turns into space is going to need a little more work.

Uncle Al said...

"The higher the density, the slower the speed of light." Refractive index. "speed of light becomes an imaginary number and its square becomes negative." Meta-materials. Maths are explicit. Physical constructions are active toward microwaves as models. "Physicists say space-time becomes Euclidean." Euclidean coordinate systems are chiral. Matter is fundamentally favored versus antimatter, chiral Weak Interaction, racemic Strong Interaction . The Equivalence Principle is violated by geometry (enantiomorphs), not by composition or field.

Parity violations, symmetry breakings, chiral anomalies, Chern-Simons repair of Einstein-Hilbert action (arXiv:0811.0181) are diagnostic. A geometric Eötvös experiment contrasts visually and chemically identical, single crystal test masses in enantiomorphic space groups, e.g., P3(1)21 vs. P3(2)21 α-quartz. It is an existing apparatus, rapid, corrective test of failed quantum gravitation.

Sabine Hossenfelder said...

kashyap: No.

Sabine Hossenfelder said...

Hi Phil,

That is correct. And that's one of the main reasons I don't like this hypothesis. Best,

B.

Frank Burdge said...

I submit that space and time are inseparable at every possible scale and temperature. And,in the absence of time,space would be a continuous void that could not be quantized.

Theophanes Raptis said...

Beware of what may lurk in such frozen silence...

http://tentaclii.wordpress.com

Perhaps Lovecraft was right after all, "That is not dead which can eternal lie. And with strange aeons even death may die."

Shantanu said...

Bee,
Just to draw attention to one more possibility to avoid big bang singularity
see
http://arxiv.org/abs/1111.4595

Theophanes Raptis said...

A Museum of Egotism and Arrogance...

http://blogs.scientificamerican.com/the-curious-wavefunction/2014/01/22/physics-and-fundamental-laws-necessary-truth-or-misleading-cacophony/

Plato Hagel said...

One is looking for an emergent system that supports, a materialistic version, so we say one is to dealing with physical cosmology?

So we do understand the universe makeup as a division "of a pie." Pie smells good, and your being quest about it, because we use a different sense of the operation of the universe. The tracker is onto something?

So an alteration with regards to this perception then one cannot use that framework?

Thinking.:)

Uncle Al said...

Can a million theorists typing Latex crack the nut absent empirical predictions to the end? Let's join the orgy in progress:

An electron neutrino is an electron stripped of its charge.

One now calculate the masses of electron, muon, and tau neutrinos. Append my name as first author when theory is complete. We'll do the rest of the universe tomorrow.

L. Edgar Otto said...

New theory challenges Uncle Al's particle theory (I just read eating Uncle Al's fig Newton cookies while wondering what European Leibintz cookies taste like).
"A charge is an electron without its neutrino."
If we take Penrose at his word that a zig or zag may as well be point particles, then the paths these make would better be described by the 60's idea that an electron is donut shaped.
But if we from outside could see thru one the zigzags would be spinning in the opposite direction. :-)

L. Edgar Otto said...

Perhaps Shhh... suggests there is a great secret so do not tell. The universe with a sense of irony for those who watch the play in the know.

These two theories and some others are at once different in approaches yet seem to contain haunting similarities.

In a sense it talks about the same physically such as our ideas of c or h or mass and energy as if these are the center or fulcrums as a frame of reference or points of departure where models complement or mirror each other or apparently do not connect.

Is gravity simply a form of energy (with some fine added details)? That inverse square law that planets do not spiral down into the sun as in an inverse cube?

These are questions of symmetry as is Maxwell's monopoles as silent. So like the apparent empty or firey horizon
is there a conceptual link to the science magazine news of yesterday of an artificial monopoles as a vortex?

The distinction of what is the nature if distance in the two theories here compared seems an important clue to the music of the spheres that comes next after the stage and then the observers, the audience if they hear by echoes and amplification in the amphitheatre.

Perhaps a Hippodrome in loops as chariots race or like Phaeton reach to catch the asymptopic sun. Or risk adventure seen as stalking like Icarius with wings of wax we fly too high in escaping time where we would be long lost blindly touching either wall in a maze.

The vector force between two objects or just from one to another is the same description, so too Cupid's arrows.

But I am just downloading the pdf of the 2011 arXiv article now.

Zephir said...

At first, the Big Bang did never happen. When the observable Universe can be described with FRLW metric, it just means, that it appears like the black hole inverted. But the event horizon of such white hole is still stationary. We aren't saying, that the event horizon of black hole is evolving in time, just because the space-time gets curved there.

Zephir said...

/* can be rewritten in a suggestively simply way, as a density-dependence of the speed of light */

Isn't it the return to "variable light speed" model? In AWT the metric expansion of space (which is allegedly responsible for the red shift) is the same effect, like the collapse of wavelength of ripples at the water surface with distance, i.e. the result of scattering of light with density fluctuations of vacuum (compare the tired light model of ingenious Fred Zwicky).

Zephir said...

/* time stops existing and turns into space */

This essentially happens near event horizon of every black hole. Being more specific, the time-like dimensions exchange their position with spatial dimension in space-time metric. The similar stuff happens at the particle horizon of observable universe.

picture

From perspective of water surface analogy of space-time such a mysterious thing is actually quite trivial: the surface ripples are getting scattered into underwater, i.e. transverse waves are scattering into longitudinal ones, which do utilize the direction perpendicular to water surface, which serves as a model of time dimension here.

The metric expansion and variable light speed models are mutually dual. We can actually postulate dozens of mutually dual models (like the "variable mass model" proposed recently), but they can be distinguished with their qualitative aspects, for example with observation of remote galaxies. In metric expansion model these galaxies should appear smaller than the nearby galaxies, in the dual model they should appear larger (which is actually, what we are observing).

mpc755 said...

The Big Ongoing replaces the Big Bang.

We know what dark energy and dark matter are.

Cosmic microwave background
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation#Low_multipoles_and_other_anomalies

“With the increasingly precise data provided by WMAP, there have been a number of claims that the CMB exhibits anomalies, such as very large scale anisotropies, anomalous alignments, and non-Gaussian distributions. … A number of groups have suggested that this could be the signature of new physics at the greatest observable scales”

The new physics is understanding our Universe is a larger version of a polar jet (http://en.wikipedia.org/wiki/Polar_jet).

Cosmos may be curved, scientists say
http://www.foxnews.com/science/2013/09/12/cosmos-may-be-curved-scientists-say/?intcmp=features

“Now cosmologists suggest these anomalies occur because the universe is not flat. Instead, these researchers propose the universe may be ever so slightly “open,” curved in such a way that parallel lines, which never converge or diverge when traveling on a flat surface, will eventually diverge from one another, like on a saddle.”

Our Universe is open because it is a larger version of a polar jet.

Was the universe born spinning?
http://physicsworld.com/cws/article/news/2011/jul/25/was-the-universe-born-spinning

“The universe was born spinning and continues to do so around a preferred axis”

Our Universe spins around a preferred axis because it is a larger version of a polar jet.

Mysterious Cosmic ‘Dark Flow’ Tracked Deeper into Universe
http://www.nasa.gov/centers/goddard/news/releases/2010/10-023.html

“The clusters appear to be moving along a line extending from our solar system toward Centaurus/Hydra, but the direction of this motion is less certain. Evidence indicates that the clusters are headed outward along this path, away from Earth, but the team cannot yet rule out the opposite flow. “We detect motion along this axis, but right now our data cannot state as strongly as we’d like whether the clusters are coming or going,” Kashlinsky said.”

The clusters are headed along this path because our Universe is a larger version of a polar jet.

It’s not the Big Bang; it’s the Big Ongoing.

Dark energy is the evaporated matter (i.e. aether) which is continually being emitted into the Universal jet.

There is no such thing as non-baryonic dark matter anchored to matter. Matter moves through and displaces the aether.

Aether has mass, physically occupies three dimensional space and is physically displaced by the particles of matter which exist in it and move through it.

Displaced aether pushing back and exerting inward pressure toward matter is gravity.

The state of displacement of the aether is gravity.

There is evidence of the aether every time a double slit experiment is performed; it’s what waves.

L. Edgar Otto said...

mock 755
This is closer to a bigger picture but as to where the information goes while ongoing also by laws uniform and timelike intrinsic and intimate as a minimum or no distance as aether in all its senses, divisions or mergings, rests and motions and directions : The displacement can still be Zero.