[guest48150]

What happened before the Big Bang?? Can anyone explain in simple words the theory of quantum loop gravity?? Thanks.

[yor_on]

Nobody knows :)

[syhprum]

One can only guess there can never be any evidence , my guess is that there is an infinite cycle of compression and expansion.

[set fair]

One can only guess there can never be any evidence

Since we can only guess, how can you say cataorically there can never be any evidence?

[chris]

The type of question is quite similar to this old chestnut:

https://www.thenakedscientists.com/articles/questions/what-universe-expanding

[yor_on]

That one is answerable if you think of it as connections. It doesn't need 'dimensions', it makes 'dimensions'. The one with the Big Bang is much trickier.

[Bogie_smiles]

First, since it appears that the original poster has left this thread adrift, and because the title of the thread is classic, I want to reply, to see if we can discuss preconditions to the Big Bang without overstepping the NSF guidelines for hard science sub-forums:

I don’t object to the statement that evidence that predates the Big Bang is generally considered little more than a guess, but that may not apply to all of the evidence. Are you familiar with the mapping of the cosmic microwave background that has yielded what they call the "cold spot”?
https://en.wikipedia.org/wiki/CMB_cold_spot

http://sci.esa.int/science-e-media/img/67/Planck_anomalies_Bianchi_on_CMB_orig.jpg

http://sci.esa.int/planck/51559-hemispheric-asymmetry-and-cold-spot-in-the-cosmic-microwave-background/

“Two Cosmic Microwave Background anomalous features hinted at by Planck's predecessor, NASA's Wilkinson Microwave Anisotropy Probe (WMAP), are confirmed in the new high precision data from Planck.  One is an asymmetry in the average temperatures on opposite hemispheres of the sky (indicated by the curved line), with slightly higher average temperatures in the southern ecliptic hemisphere and slightly lower average temperatures in the northern ecliptic hemisphere. This runs counter to the prediction made by the standard model that the Universe should be broadly similar in any direction we look. There is also a cold spot that extends over a patch of sky that is much larger than expected (circled). In this image the anomalous regions have been enhanced with red and blue shading to make them more clearly visible.”


And this arxiv PDF that gives one justification for considering the observed hemispherical anisotropy in the heat map to be related to a cosmological primordial power spectrum produced during inflation.
https://arxiv.org/pdf/1503.03859.pdf

Standard Big Bang Theory does not predict conditions that could cause the observed hemispherical temperature variance, or the cold spot.


There is always cause and effect, and there can be some debate about what might cause the primordial power spectrum to display that particular pattern of anisotropy. One suggested explanation for the presence of the cold spot in our big bang heat map is that it implies the presence of another universe, or what I would call another expanding big bang event adjacent to ours. The explanation includes the reasoning that resulting gravitational attraction between the two of them is “pulling” on the stars and galaxies in that region of our event heat map, implying a multiple big bang landscape. A similar nearby big bang event would not only explain the cold spot, but would also suggest an explanation for the hemispherical anisotropy, i.e., suggesting multiple big bang landscape that could reasonably produce preconditions to our own big bang event that would result in the hemispherical anisotropy.

[PmbPhy]

What happened before the Big Bang?? Can anyone explain in simple words the theory of quantum loop gravity?? Thanks.

Nobody knows for certain. Especially since the big ang id not a moment in time but a theory. There are theories which postulate what happen befoe a certain time but nobody knows for certain. I don't know those theories so I can't help there.

[Bogie_smiles]

Standard Big Bang Theory does not predict conditions that could cause the observed hemispherical temperature variance, or the cold spot.

Research paper addressing “Before the Big Bang”

https://www.researchgate.net/publication/279446746_Graviton_and_cosmology_equations_before_the_Big_Bang
“For long time seemed the Friedmann equation is able to explain universe, but in recent years, the cosmological constant was of interest to cosmologists. However, these two equations are unable to explain before the Big Bang. Thus this paper, from a new approach, turns out to merge the fundamental principles of quantum physics, relativity and classical mechanics through a new definition of rest state of particles like photon, and attempts to present the reasons and the possibilities of the existence of the superluminal speeds. So according to this new view some complex concepts and unanswered questions is explained in this paper.”


Hossein Javadi PDF
http://gsjournal.net/Science-Journals/Research%20Papers-Cosmology/Download/6120



Researchers Blog

https://scienceblogs.com/startswithabang/2012/10/15/what-happened-before-the-big-bang

Excerpt:
“As the Universe expands and cools, gravity works to pull the matter and energy in on itself, making overdensities bigger and underdensities smaller, while radiation pressure works to wash those fluctuations out. Normal matter (protons, neutrons, and electrons) interacts with photons and itself, creating "bouncy" features in this pattern of fluctuations, while dark matter can feel the radiation pressure and the gravitational tugs, but has no cross-section with either normal matter, photons or itself.
As a result, we learn what the different components of the Universe are.”

Science professionals are at work with the WMAP and Planck Survey data, and their efforts are continually advancing our knowledge, and the acceptance of preconditions to the Big Bang.

[Bogie_smiles]

This youtube video seems to be quite a complete presentation on the cold spot:

https://www.youtube.com/watch?v=PQHhLHh_8go

[Bogie_smiles]

And you can learn a lot about the Cosmic Microwave Background Radiation (CMBR) from this youtube video:

[Bogie_smiles]

https://www.youtube.com/watch?v=SPtSBLpyBu4

One thing that I don’t think was made obvious by the youtube videos in my last two posts is the extent to which voids make up much of the structure of the observable universe. The videos mention Boötes void,

https://en.wikipedia.org/wiki/Boötes_void

which is large, but it is far down the list of the largest voids,

https://en.wikipedia.org/wiki/List_of_largest_cosmic_structures#List_of_largest_voids

Boötes void is particularly anomalous because it lies between us and the cold spot, and because of its very low galaxy density (only ~60 galaxies detected in the whole huge void.

There is a connection between voids in general, and the large scale structure of galaxies and surrounding accumulations of dark matter. Relative to Boötes void, there are many much larger voids that have been mapped, and that exist among the filament-like large scale structures of galaxies.

https://en.wikipedia.org/wiki/List_of_voids

https://en.wikipedia.org/wiki/Galaxy_filament

https://en.wikipedia.org/wiki/Void_(astronomy)

http://cosmicweb.uchicago.edu/filaments.html

[Bogie_smiles]

I copied this statement from ChiralSPO’s thread about “How fundamental is time?” because it expresses the right sentiment for this thread that explores “What happened before the Big Bang”.

Please note: This thread may sit on the edge of generally accepted science and speculation. I would like to keep it in this sub-forum (which is intended for discussions of generally accepted science), so let us agree to be clear about when we are speculating/hypothesizing.  Thanks!

http://hubblesite.org/news_release/news/2018-34
This is an article on the Hubblesite from July 2018, quite current.


“Using the powerful Hubble and Gaia space telescopes, astronomers just took a big step toward finding the answer to the Hubble constant, one of the most important and long-sought numbers in all of cosmology. This number measures the rate at which the universe is expanding since the big bang, 13.8 billion years ago. The constant is named for astronomer Edwin Hubble, who nearly a century ago discovered that the universe was uniformly expanding in all directions. Now, researchers have calculated this number with unprecedented accuracy.

Intriguingly, the new results further intensify the discrepancy between measurements for the expansion rate of the nearby universe, and those of the distant, primeval universe — before stars and galaxies even existed. Because the universe is expanding uniformly, these measurements should be the same. The so-called “tension” implies that there could be new physics underlying the foundations of the universe.”

“Possibilities include the interaction strength of dark matter, dark energy being even more exotic than previously thought, or an unknown new particle in the tapestry of space.”

“Combining observations from NASA’s Hubble Space Telescope and the European Space Agency’s (ESA) Gaia space observatory, astronomers further refined the previous value for the Hubble constant, the rate at which the universe is expanding from the big bang 13.8 billion years ago.
But as the measurements have become more precise, the team’s determination of the Hubble constant has become more and more at odds with the measurements from another space observatory, ESA’s Planck mission, which is coming up with a different predicted value for the Hubble constant.
Planck mapped the primeval universe as it appeared only 360,000 years after the big bang. The entire sky is imprinted with the signature of the big bang encoded in microwaves. Planck measured the sizes of the ripples in this Cosmic Microwave Background (CMB) that were produced by slight irregularities in the big bang fireball. The fine details of these ripples encode how much dark matter and normal matter there is, the trajectory of the universe at that time, and other cosmological parameters.

These measurements, still being assessed, allow scientists to predict how the early universe would likely have evolved into the expansion rate we can measure today. However, those predictions don’t seem to match the new measurements of our nearby contemporary universe.
“With the addition of this new Gaia and Hubble Space Telescope data, we now have a serious tension with the Cosmic Microwave Background data,” said Planck team member and lead analyst George Efstathiou of the Kavli Institute for Cosmology in Cambridge, England, who was not involved with the new work.
“The tension seems to have grown into a full-blown incompatibility between our views of the early and late time universe,” said team leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute and the Johns Hopkins University in Baltimore, Maryland. “At this point, clearly it’s not simply some gross error in any one measurement. It’s as though you predicted how tall a child would become from a growth chart and then found the adult he or she became greatly exceeded the prediction. We are very perplexed.”
In 2005, Riess and members of the SHOES (Supernova H[size=0pt]0[/size] for the Equation of State) Team set out to measure the universe’s expansion rate with unprecedented accuracy. In the following years, by refining their techniques, this team shaved down the rate measurement’s uncertainty to unprecedented levels. Now, with the power of Hubble and Gaia combined, they have reduced that uncertainty to just 2.2 percent.
Because the Hubble constant is needed to estimate the age of the universe, the long-sought answer is one of the most important numbers in cosmology. It is named after astronomer Edwin Hubble, who nearly a century ago discovered that the universe was uniformly expanding in all directions—a finding that gave birth to modern cosmology.
Galaxies appear to recede from Earth proportional to their distances, meaning that the farther away they are, the faster they appear to be moving away. This is a consequence of expanding space, and not a value of true space velocity. By measuring the value of the Hubble constant over time, astronomers can construct a picture of our cosmic evolution, infer the make-up of the universe, and uncover clues concerning its ultimate fate.
The two major methods of measuring this number give incompatible results. One method is direct, building a cosmic “distance ladder” from measurements of stars in our local universe. The other method uses the CMB to measure the trajectory of the universe shortly after the Big Bang and then uses physics to describe the universe and extrapolate to the present expansion rate. Together, the measurements should provide an end-to-end test of our basic understanding of the so-called “Standard Model” of the universe. However, the pieces don’t fit.
Using Hubble and newly released data from Gaia, Riess’ team measured the present rate of expansion to be 73.5 kilometers (45.6 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 73.5 kilometers per second faster. However, the Planck results predict the universe should be expanding today at only 67.0 kilometers (41.6 miles) per second per megaparsec. As the teams’ measurements have become more and more precise, the chasm between them has continued to widen, and is now about 4 times the size of their combined uncertainty.
Over the years, Riess’ team has refined the Hubble constant value by streamlining and strengthening the “cosmic distance ladder,” used to measure precise distances to nearby and far-off galaxies. They compared those distances with the expansion of space, measured by the stretching of light from nearby galaxies. Using the apparent outward velocity at each distance, they then calculated the Hubble constant.
To gauge the distances between nearby galaxies, his team used a special type of star as cosmic yardsticks or milepost markers. These pulsating stars, called Cepheid variables, brighten and dim at rates that correspond to their intrinsic brightness. By comparing their intrinsic brightness with their apparent brightness as seen from Earth, scientists can calculate their distances.
Gaia further refined this yardstick by geometrically measuring the distance to 50 Cepheid variables in the Milky Way. These measurements were combined with precise measurements of their brightnesses from Hubble. This allowed the astronomers to more accurately calibrate the Cepheids and then use those seen outside the Milky Way as milepost markers.
“When you use Cepheids, you need both distance and brightness,” explained Riess. Hubble provided the information on brightness, and Gaia provided the parallax information needed to accurately determine the distances. Parallax is the apparent change in an object’s position due to a shift in the observer’s point of view. Ancient Greeks first used this technique to measure the distance from Earth to the Moon.
“Hubble is really amazing as a general-purpose observatory, but Gaia is the new gold standard for calibrating distance. It is purpose-built for measuring parallax—this is what it was designed to do,” Stefano Casertano of Space Telescope Science Institute and a member of the SHOES Team added. “Gaia brings a new ability to recalibrate all past distance measures, and it seems to confirm our previous work. We get the same answer for the Hubble constant if we replace all previous calibrations of the distance ladder with just the Gaia parallaxes. It’s a crosscheck between two very powerful and precise observatories.”
The goal of Riess’ team is to work with Gaia to cross the threshold of refining the Hubble constant to a value of only one percent by the early 2020s. Meanwhile, astrophysicists will likely continue to grapple with revisiting their ideas about the physics of the early universe.
The Riess team's latest results are published in the July 12 issue of the Astrophysical Journal.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.”

[yor_on]

Interesting

I don't know, but I would probably first look at the projections of the cmb (cosmic background radiation)
doesn't mean that I don't respect the idea of 'standard candles' setting a standard for measuring a distance.

https://www.forbes.com/sites/kionasmith/2018/07/05/how-henrietta-leavitt-lit-the-way-to-distant-galaxies/

[evan_au]

One cosmology lecturer reportedly defined the scope of his course as "T > 0".

...where T is time after the Big Bang.

[Bogie_smiles]

One cosmology lecturer reportedly set the limits on his course as "T > 0".

...where T is time after the Big Bang.

Very reasonable from the perspective that the evidence supports a Big Bang, and from the perspective that if the lecturer didn't set that limit, who knows what preconditions might come out of student's minds .

The WMAP and Planck Survey evidence showing the cold spot and the hemispherical anomalies might cause the lecturers these days to set the limit at T > 0 with an eye to what the observables might say about -T.

[Bogie_smiles]

-T is intended to suggest that though T marked the Big Bang event itself, i.e., the event that initiated the expansion of the observable universe, there was time prior to T during which there logically were preconditions that caused the Big Bang. Are there any objections to that line of reasoning being discussed in this sub−forum?

[Colin2B]

Are there any objections to that line of reasoning being discussed in this sub−forum?

It depends whether you intend to take it into new theory speculations, as you have previously.
You can’t just use this section as a new theory launch point.

[yor_on]

Actually the evidence for this universe being both isotropic and homogeneous are quite overwhelming. As far as I see physics concepts is just about this. And it fits both astronomically as well as on a purely theoretical plane, aka symmetries, etc. There should be a truth there. On the other tentacle you will find that a 'Big Bang', using the logic Bill pointed out in another thread, always starts where you are, you're the 'center' of it, assuming this isotropy and homogeneous universe.

Furthermore it doesn't matter for this if you're in relative motion, or depending on what time you 'time reverse' the universe into that 'original point'. It will hold. You might call this another type of 'symmetry' too I guess, but of what kind is harder to say.

[Bogie_smiles]

It depends whether you intend to take it into new theory speculations, as you have previously.
You can’t just use this section as a new theory launch point.

Fair enough. I’m not intending to push the guidelines to the breaking point, but asking if there is a definable line that shouldn’t be crossed. If the line is that discussion of causes and effects related to events before T = 0 automatically fall into the speculative category, and therefore cross the line, then the guidelines could simply be that discussions of preconditions to the Big Bang should be reserved for New Theories.

Reason would say that in the event of some new evidence of preconditions, the guidelines would allow discussion of it. Bringing up generally accepted observations that might hold clues to possible preconditions to T = 0, like the cold spot and the hemispherical anisotropy of the CMBR, has been allowed, so are we going out on thin ice by mentioning possible causes and effects related to “-T” that are suggested by those observations?