Big Bounce--SciAm cover story October 2008

[Martin]

The cover of the October 2008 Scientific American says Forget the Big Bang!

 

The cover story inside is by my namesake, a top quantum cosmologist named Martin Bojowald, and is titled Big Bang or Big Bounce?

http://www.sciam.com/article.cfm?id=big-bang-or-big-bounce

At the moment it is available free, so if you are interested it would probably be a good idea to check it out. They sometimes put articles on a pay-per-view basis later.

 

As a summary, the SciAm editors identified these as the key concepts, but the actual article has a lot more in it:

=====quote====

Key Concepts

 

* Einstein’s general theory of relativity says that the universe began with the big bang singularity, a moment when all the matter we see was concentrated at a single point of infinite density. But the theory does not capture the fine, quantum structure of spacetime, which limits how tightly matter can be concentrated and how strong gravity can become. To figure out what really happened, physicists need a quantum theory of gravity.

* According to one candidate for such a theory, loop quantum gravity, space is subdivided into “atoms” of volume and has a finite capacity to store matter and energy, thereby preventing true singularities from existing.

* If so, time may have extended before the bang. The prebang universe may have undergone a catastrophic implosion that reached a point of maximum density and then reversed. In short, a big crunch may have led to a big bounce and then to the big bang.

===endquote===

 

The article is 5 pages plus three pages of diagrams and graphics illustrating the ideas.

[CaptainPanic]

The general idea makes sense in a universe that is just full of oscillating phenomena.

 

disclaimer: I'm no expert in quantum stuff

[JTankers]

The theory is compelling. I like the line of conjecture at bigcrash.org.

[Arch2008]

I posted elsewhere that Neil Turok reasoned that the cosmological constant was lower than it should be and that a cyclic universe would explain this. As for LQG, I think its proponents have to answer some serious criticism:

http://motls.blogspot.com/2007/07/loop-quantum-cosmology.html

[Martin]

Would somebody like to spell out some specific criticisms of either LQG or LQC---with links to professional research papers with specific stuff quoted, so we can know what is being talked about? Neither vague internet rants nor popularizations for wide audience normally connect with reality.

[Arch2008]

Well, this is what we are talking about:

http://relativity.livingreviews.org/Articles/lrr-2005-11/

And of course, the “rants” are what we apparently don’t want to talk about. Someone is choosing what gets researched, as we’ve already addressed. If LQG/LQC is a path to enlightenment that is beyond answering any criticism, then that doesn’t sound very scientific to me. Rants and vague criticism should be simple to address, if this is indeed a viable theory. If answers cannot be explained to wide audiences, then maybe they are not answers. So, why is this the path?

[Martin]

... So, why is this the path?

You mean, I guess, what's good about it----why have so many researchers jumped in over the past 3 or 4 years? That seems like a constructive question.

 

In theoretical research fields there should not be just one path that is "THE" path, I think it's safe to say. And Loop Cosmology (LQC) is just one type of non-singular cosmology or bounce cosmology. But it is increasingly prominent, and one can well ask why? As you do! So I'll try to respond.

 

To answer systematically, from my standpoint as an observer, I should first make clear that it has become a hot line of research, and, measuring objectively by citations and the output of highly cited papers, has taken the lead away from string and others in the quantum cosmology department.

 

There are also other types of objective recognition, like the Xanthopoulos prize for cosmology-related research, like who is invited to speak major international conferences, like professional society elections. Not all objective measures need necessarily to agree, but a sufficient number in fact do. There has been a shift.

 

It's important to know what's been going on. Our discussion should be based on facts (not on vague impressions from somebody's alternative reality). So I will trot out some facts, as time permits.

[Severian]

When they can make a testable prediction, I will start to take them seriously.

[Martin]

We'll talk about testable predictions later. There are a lot of aspects to this.

OK, so let's approach things gradually. I'll explain what's been happening and then we can discuss why, and whether it's a good thing or not, and what it means longterm etc.

 

Here's a search of QC publication with date > 2004, cites-ordered.

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+2004&FORMAT=www&SEQUENCE=citecount%28d%29

Look at the top 10 or 20----it's mostly Loop

 

Now here's the same search for 92<date<97.

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+1992+AND+DATE+%3C+1997&FORMAT=www&SEQUENCE=citecount%28d%29

Look at the top 10 or 20----it's mostly String, plus allied brane and eternal inflation stuff.

 

the highly cited papers are the ones that the researchers themselves value most highly---refer to the most, find to be the most useful or significant research

 

If you look at the same search for date >2005, that is even more recent, you find that 18 of the top 20 are Loop. That is Loop started from a situation where quantum cosmology was dominated by string and string-inspired papers, ten years ago, and has made almost a clean sweep.

 

Later we can ask why, is this good or bad, what does it mean longterm. But for now lets get some more information and fill in the picture with more detail.

[Arch2008]

Thanks Martin! I'm really not trying to be a troll or something like that. I am very interesting in learning about this, but I have a skeptical mind (which you may have already gathered about me).

 

Also Severian, someone at another site thinks that the prediction of high energy light waves having a different speed may be a prediction the can be tested via GRB's.

http://www.physicsforums.com/showthread.php?t=257483

Edited September 19, 2008 by Arch2008

[fredrik]

My primary interest has never been cosmology, but I want to claim that these reasonings nevertheless touches in an interesting way other foundations of physics and that some of the foundational things of cosmology, do show analogous to other problems of foundational physics, such as QM and observer physics. So in a deeper sense these reasoning in these papers may extend beyond cosmology.

 

In some ways I see the "creation of the universe" to have similarities to the "creation of observers". In particular if you have the view that physical interactions is best described as relational interactions, and where physical interactions can bee seen as communication between sub-systems/observers, and that they basically learn about each other, and respond to this information; meaning the local actions are based on the local image of the environment. This might suggest that the physical meaning of bohrs old expression is deeper than the original intention.

 

And intuitive understandings of one thing, might help the other too.

 

My two favourite sections in that article is

 

"The big bang is no longer a physical beginning or a mathematical singularity, but it does put a practical limitation on our knowledge. Whatever survives cannot provide a complete view of what came before.

 

Frustrating as this may be, it might be a conceptual blessing. In physical systems as in daily life, disorder tends to increase. This principle, known as the second law of thermodynamics, is an argument against an eternal universe. If order has been decreasing for an infinite span of time, the universe should by now be so disorganized that structures we see in galaxies as well as on Earth would be all but impossible. The right amount of cosmic forgetfulness may come to the rescue by presenting the young, growing universe with a clean slate irrespective of all the mess that may have built up before."

 

Rather than pick on details that they admitt thesemlves (like the omitt matter etc) I think there are some nice grains in there that can guide us in the quest for incorporating matter.

 

So the problem of the origin of the universe, has similarities with the origin of observers, in the sense that there observers typically also have finite lifespans, and there are many of them that are furthermore interacting to varying extent. Similarly could one imagine the galaxy as one obervers (with internal structure), but what is the largest possible obeserver relative to us?

 

/Fredrik

[lucaspa]

Martin Bojowald has an article about loop quantum cosmology in the Oct 2008 issue of Scientific American: http://www.sciam.com/article.cfm?id=big-bang-or-big-bounce

 

I've got a few questions after reading the article and am hoping someone more familiar with more of Bojowald's work can help answer them.

 

 

Bojowald states:

"loop quantum gravity suggests that the atomic structure of spacetime changes the nature of gravity at very high energy densities, making it a repulsive. ... Because of the the quantum-gravitational change in the balance of forces, no singularity -- no state of infinite density -- can ever arise." [emphasis mine].

 

Question: Aren't black holes singularities and have infinite density? They are observed. Does Bojowald discuss this contradictory evidence to his statement anyplace else?

 

On pages 50-51 there is a figure entitled "Replacing the Bang". "In one scenario, the universe is eternal. It imploded, reached the maximum allowable density (at the bounce), and blew apart again."

 

However, recent data shows that our universe is expanding and will never collapse. Loop quantum gravity seems to predict and explain inflation, but Bojowald never says in this article that it explains dark energy (the expansion force).

 

Question: If the "eternal" scenario is accurate there would have been a huge number of bounces before our universe. How likely is it that we would happen to be in the last universe in such a series? Or why would it be, under that scenario, that the result of a bounce would be a universe that will die and not implode?

 

Back in the 1970s and 1980s the idea of an infinite series of expansion/collapse cycles was discarded due to problems induced by the second law of thermodynamics. Basically, entropy would increase so that after a few cycles, a universe like ours would be impossible.

 

Bojowald talks a bit about thermodynamics:

"According to traditional thermodynamics, there is no such thing as a truly clean slate; every system always retains a memory of its past in the configuration of its atoms ... But by allowing the number of spacetime atoms to change, loop quantum gravity allows the universe more freedom to tidy up than classical physics suggests."

 

This, it seems to me, doesn't get around the problem posed by thermodynamics. "more freedom" doesn't correspond to "completely free slate" and that still leaves the problem of entropy and its effect on the next universe. What I take away from this is that loop quantum cosmology can extend the number of cycles before a universe like ours is impossible, but can't make the cycles "infinite".

 

Question: Does Bojowald discuss the effects of thermodynamics on repeated bounces anywhere else and, if so, what does he say?

 

Bojowald states that one testable effect of loop quantum gravity is: "light of different wavelengths travel at different speeds. Although these differences are tiny, they may add up during a long trip."

 

Don't we have "long trips" in the case of objects at very high redshift? And don't we measure the redshift by looking at spectral lines at different wavelengths that have been redshifted? Wouldn't traveling at different speeds change the relationship of those spectral lines somewhat, giving different redshift numbers for different lines for the same object? Has that been looked at?

 

These are questions that occur to a biochemist/tissue engineer. I'm thinking they must have occurred to Bojowald as well. If so, I wish he would have been a bit more thorough in the SciAm article.

[D H]

Lucapsa: I merged your post into this existing thread on this topic. Now to address some of the questions you raised.

 

Caveat: I am not a cosmologist. My answers may well be incorrect.

 

Question: Aren't black holes singularities and have infinite density? They are observed.

Black holes most likely have been observed. We do not, however, know exactly what they are. In other domains in physics, the presence of singularities is indicative of a problem with the physical model rather than the physical system being modeled. That general relativity predicts black holes, i.e. volumes where spacetime is so highly curved that even light cannot escape, is well-accepted. That GR further predicts that the material forms a mathematical singularity is not so well-accepted. Many physicists see this as indicative that GR itself is flawed.

 

Question: If the "eternal" scenario is accurate there would have been a huge number of bounces before our universe. How likely is it that we would happen to be in the last universe in such a series? Or why would it be, under that scenario, that the result of a bounce would be a universe that will die and not implode?

The first thing to remember is that, IMHO, this article is highly conjectural. It hints at some future tests. Another thing to remember is that we do not yet know the ultimate fate of the universe. Last I read, the jury was still out.

 

Just because our universe might not collapse in on itself does not necessarily mean our universe is "the end of the line." Other physicists have conjectured that the formation of a black hole may lead to the creation of a universe. If that is the case, our universe may well have already spawned a whole slew of universes.

 

Back in the 1970s and 1980s the idea of an infinite series of expansion/collapse cycles was discarded due to problems induced by the second law of thermodynamics. Basically, entropy would increase so that after a few cycles, a universe like ours would be impossible.

That implicitly assumes things are conserved from one universe to another. What makes you think they are? The conservation laws derive from Noether's first theorem. For example, conservation of energy results from the homogeneity of time. Time is not homogeneous across the "bounce". Bojowald similarly implies that the second law of thermodynamics does not apply across the "bounce".

 

 

Bojowald states that one testable effect of loop quantum gravity is: "light of different wavelengths travel at different speeds. Although these differences are tiny, they may add up during a long trip."

 

Don't we have "long trips" in the case of objects at very high redshift? And don't we measure the redshift by looking at spectral lines at different wavelengths that have been redshifted? Wouldn't traveling at different speeds change the relationship of those spectral lines somewhat, giving different redshift numbers for different lines for the same object? Has that been looked at?

There are some signs that the speed of light does vary slightly with wavelength. For example, see this article, Gamma Ray Delay May Be Sign of 'New Physics'.

Edited September 23, 2008 by D H
Add caveat

[lucaspa]

Black holes most likely have been observed. We do not, however, know exactly what they are.

 

Black holes are cases where a massive star collapses such that "The star eventually collapses to the point of zero volume and infinite density," http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html That is a singularity and I've always read black holes being called singularities. Notice that this "infinite density" is what Bojowald says can't happen. So why don't black holes "rebound" at that point? Categorically he says singularities can't happen. Black holes are singularities.

 

With all respect, you aren't addressing the question. You are proposing instead that black holes are not the singularities they've been accepted as being. But you have no data for that. What we need is how Bojowald addresses the issue. If he doesn't, then that is a problem with his hypothesis.

 

See that site mentioned above for observations. Also see:

1. RP van der Marel, PT de Zeuw, H-W Rix, GD Quinian, A massive black hole at the centre of the quiescent galaxy M32. Nature 385: 610-612, Feb. 13 1997.

2. J Green, Visions of black holes. Science 275: 476-478, Jan 24 1997.

5. R Irion, Black holes begin to lose their mystery. Science 287: 411, Jan 21, 2000. Describes observed black holes

 

That GR further predicts that the material forms a mathematical singularity is not so well-accepted. Many physicists see this as indicative that GR itself is flawed.

 

That's not the problem as I've read the literature. The mathematical singularity is very well accepted. The problem is rather that GR itself breaks down at the singularity. Having a theory that breaks down in part of the universe is a problem for the theory. But it is the data of singularities that leads to thinking that GR is flawed, not the mathematics.

 

The first thing to remember is that, IMHO, this article is highly conjectural. It hints at some future tests. Another thing to remember is that we do not yet know the ultimate fate of the universe. Last I read, the jury was still out.

 

The conclusions were not stated as conjectural. However, a "conjecture" is still a hypothesis and we can always test hypotheses against existing data. When was the last you read? It was always accepted that the visible matter was not enough to cause a collapse but that with the addition of dark matter a collapse was possible. As long as the expansion was slowing. Since it has been observed that the expansion is accelerating, there is no way the universe can collapse:

7. J Glanz, Exploding stars point to a universal repulsive force. Science 279:651-652, 30 Jan. 1998. New data indicates the cosmological constant is back.

7a. J Glanz, No backing off from the accelerating universe. Science 282: 1249-1250, Nov. 13, 1998. As the title says, 2 independent and competing groups continue to get data that agrees.

8. G Tarke and S.P. Swordy, Cosmic Antimatter. Scientific American, 278(4): 36-41, April 1998.

10. CJ Hogan, RP Kirshner, and NB Suntzeff, Surveying space-time with supernovae. Scientific American, 280: 46-51, Jan. 1999. Studies indicate that the rate of expansion of the universe is accelerating.

11. LM Krauss, Cosmological antigravity. Scientific American, 280: 52-61, Jan. 1999. discusses cosmological constant to explain accelerating expansion.

12. MA Buchner and DN Spergel. Scientific American, 280: 62-71, Jan. 1999. Discusses changes in inflationary theory to account for new observations.

13. M Livio, Cosmic explosions in an accelerating universe, Science 286: 1689-1690, Nov. 26, 1999.

13a. Web sites for expanding universe

http://www.cnn.com/TECH/space/9802/...ating.universe/

http://www.space.com/scienceastrono...celerating.html

http://www.er.doe.gov/Sub/Accomplis...scovery/43.html

 

Just because our universe might not collapse in on itself does not necessarily mean our universe is "the end of the line."

 

In terms of this hypothesis, it does. This hypothesis for a never-ending universe requires the previous universe to collapse. What other physicists have conjectured are different hypotheses. We currently aren't concerned about those.

 

That implicitly assumes things are conserved from one universe to another. What makes you think they are? The conservation laws derive from Noether's first theorem. ... Bojowald similarly implies that the second law of thermodynamics does not apply across the "bounce".

 

Actually, Bojowald says that things are conserved from one universe to another. and that the second law would apply across the bounce. Didn't you read the quotes from the article? "According to traditional thermodynamics, there is no such thing as a truly clean slate; every system always retains a memory of its past in the configuration of its atoms ... But by allowing the number of spacetime atoms to change, loop quantum gravity allows the universe more freedom to tidy up than classical physics suggests."

 

But that "more freedom" doesn't mean "completely clean up". After all, Bojowald thinks that some of the earlier state is preserved! BTW, the first law of thermodynamics is the "conservation law". We are talking about the second law and who the hell is "Noether"?

 

In the previous paragraph Bojowald talks about the second law as applying within our universe. However, that fudges the problem the second law poses for a collapse and bounce. Because of entropy, the collapse can never go back to the initial state exactly. Bojowald is saying that bounce will compensate for that somewhat, allowing a return of some of the lost entropy, but he is careful to say that it won't go back to the original. That leaves us with the problem of the second law and an infinite number of bounces.

 

There are some signs that the speed of light does vary slightly with wavelength. For example, see this article, Gamma Ray Delay May Be Sign of 'New Physics'.

 

Thank you. We can get the full article at http://arxiv.org/PS_cache/arxiv/pdf/0708/0708.2889v2.pdf

 

I see this under "Conclusions" "The observed energy-dependent delay thus is a likely observation, but does not constitute a statistically firm discovery. ... We cannot exclude, however,the possibility that the delay we find, which is significant beyond the 95% C.L., is due to some energy-dependent effect at the source. 9 However, we can exclude the possibility that the observed time delay may be due to a conventional QED plasma refraction effect induced as photons propagate through the source."

 

But let's say the effect is due to some quantum gravity interaction. The authors emphatically do not associate this data with loop quantum gravity. The article has been available for a year. Does anyone know if Bojowald has tested to see whether this variation is consistent with loop quantum gravity?

[D H]

Black holes are cases where a massive star collapses such that "The star eventually collapses to the point of zero volume and infinite density," http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html That is a singularity and I've always read black holes being called singularities. Notice that this "infinite density" is what Bojowald says can't happen.

Our best model to date, general relativity, indicates that the matter collapses into a singularity. In every other branch of physics where singularities have arisen in some theory, physicists interpret the singularity as indicative of a flaw in the theory. The same is true of black holes forming singularities in general relativity. Einstein himself rejected the concept of a singularity.

 

I am going to reiterate what I said in my first response: We do not know what happens inside a black hole. This is from Wikipedia:

The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory. This breakdown is not unexpected, as it occurs in a situation where quantum mechanical effects should become important, since densities are high and particle interactions should thus play a role. Unfortunately, to date it has not been possible to combine quantum and gravitation effects in a single theory. It is however quite generally expected that a theory of quantum gravity will feature black holes without singularities.

So why don't black holes "rebound" at that point?

They might well do that. Other physicists have conjectured that the formation of a black hole triggers the formation of a new universe. For example, see http://www.npr.org/templates/story/story.php?storyId=6545246.

[dan1dad]

Ok, Im a simpleton here, but what I can understand, is that when the universe collapses, then turns inside out and re-inflates, as per the balloon description, what forces actually hold all the pieces to the outside , that are not transfered to the inside? Or does the universe just grab whatever matter is in the way , floating around it , when it inverts and refills ?

 

I think its gravity that they say holds this all together and draws things into it during the flip... but Im not sure because if the gravity turns from an attractive force, to a repulsive force, then wouldnt it kick everything in it, and around it, away from it? So it would end up an empty bubble. And how do things get into the bubble to even start a reaction that creates a universe ?

 

Or am I way off track here?

Edited September 28, 2008 by dan1dad

[Martin]

That reorientation of space is hard to picture. But a step in the right direction would be to understand the balloon analogy.

A lot of people misunderstand the balloon analogy and it messes up their thinking. Maybe I'll start a thread. If there is any interest maybe some others like Klaynos, Gilded, etc will help out.

 

If you understand what the balloon analogy supposed to teach you, then you realize that there is no space inside or outside of the balloon. It is supposed to let you focus your mind so that only the 2D surface of the balloon exists, and there are no directions off the balloon surface which a 2D being could point his finger.

 

the analogy is for us in 3D space that there are no other directions that we 3D beings can point a finger----if you go by the analogy, then no other directions exist

 

the purpose of an analogy like this is not to explain something to you or convince you of something, it is a mental exercise to train your mind, especially your imagination.

 

 

==================

 

about orientation, think of xyz coordinates in standard orientation---turning a screw from x to y in the xy plane would drive the screw in the z direction.

if space experiences a change in orientation (going through a quantum regime where there is no fixed geometry and coming out with reverse orientation) that means that the coordinates will by like yxz. the lefthand rule instead of the righthand rule. the coordinates are now in non-standard orientation. I can't draw pictures for you but maybe you can figure it out.

[J.C.MacSwell]

http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html

 

With all respect, you aren't addressing the question. You are proposing instead that black holes are not the singularities they've been accepted as being. But you have no data for that. What we need is how Bojowald addresses the issue. If he doesn't, then that is a problem with his hypothesis.

 

 

If he simply stated that it wasn't a singularity, how would that change any of the observable or predictable aspects of a black hole?

[Tsadi]

Our best model to date, general relativity, indicates that the matter collapses into a singularity. In every other branch of physics where singularities have arisen in some theory, physicists interpret the singularity as indicative of a flaw in the theory. The same is true of black holes forming singularities in general relativity. Einstein himself rejected the concept of a singularity.

 

I am going to reiterate what I said in my first response: We do not know what happens inside a black hole. This is from Wikipedia:

The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory. This breakdown is not unexpected, as it occurs in a situation where quantum mechanical effects should become important, since densities are high and particle interactions should thus play a role. Unfortunately, to date it has not been possible to combine quantum and gravitation effects in a single theory. It is however quite generally expected that a theory of quantum gravity will feature black holes without singularities.

 

They might well do that. Other physicists have conjectured that the formation of a black hole triggers the formation of a new universe. For example, see http://www.npr.org/templates/story/story.php?storyId=6545246.

 

Well, singularities don't need to exist, in our mathematics. There was a time when Hawking considered the singularity, and realized, not only just one could exist (namely the big bang), but in fact an infinite amount of singularities could exist. And this bothered Hawking.

 

In the 1970's (i think), Hawking was fixated on the singular problem, so he introduced quantum mechanics at the very dawn of time, and by doing so, this meant that even quantum events where occurring during the big bang. By introducing quantum mechanics, when the laws where supposed to break down, removed singularities completely, and replaced it with a wormhole.

 

So we don't need singularities any more, a common mistake people still believe in, even professional scientists. We can actually deal with a theory that doesn't permit them.

[D H]

Well, singularities don't need to exist, in our mathematics. There was a time when Hawking considered the singularity, and realized, not only just one could exist (namely the big bang), but in fact an infinite amount of singularities could exist. And this bothered Hawking. In the 1970's (i think), Hawking was fixated on the singular problem, so he introduced quantum mechanics at the very dawn of time, and by doing so, this meant that even quantum events where occurring during the big bang. By introducing quantum mechanics, when the laws where supposed to break down, removed singularities completely, and replaced it with a wormhole.

Whoa! There are a lot of problems here. To name a few,

• You are conflating the big bang singularity, which is what the SciAm article addresses, with black hole singularities, which is the subject of the post you referenced.
  
• There is too much aggrandizement of Hawking in your post. Stephen Hawking is not the be-all and end-all in cosmology. Moreover, he has not reconciled quantum mechanics and general relativity. Nobody has, yet.
  
• That wormhole statement is, well, bizarre.
  
• The Penrose-Hawkings singularity theorems do indicate that gravity is singular, assuming general relativity is true. You have Hawking's work exactly backwards. Also note that Hawking's name is second in these theorems.

[Tsadi]

The post truely was innocent to show we don't need to have singularities. Nothing more and nothing less. However, just to address some of your points;

 

Why is the wormhole statement bizarre? Here's a little cosmological physics for you: Depending on what state our universe began in, the beginning of the universe can contain either a singular region, or a wormhole: A topological opening in space and time linking this universe with another universe.

 

If our universe began in a ground state, then the beginning of the universe will look more like a singularity. However, if it began in an excited state, then the universe will have begun with one of these topological openings, we call wormholes.

 

And i don't have Hawkings work backwards AT ALL. I know my stuff quite well; Hawking no longer believes that singularities exist, because YOU CAN apply quantum mechanics at the beginning of time.

 

DH, i am very sure you are a good physicist, but just as you try and not give Hawking the honor he deserves, by saying to me he is not the all and be all of cosmological physics, i'm affraid to inform you he is yet the best at the moment, so when i am going to qoute him, i will do so with great beleif he has more understanding into the subject either me or you will ever have.

 

Good day

[D H]

General relativity says singularities exist. General relativity is the best model of spacetime we have. Some even more bizarre things than singularities (e.g., wormholes) might arise, but saying they are fact is just wrong. They are purely conjectural. You appear to be young and you appear to have read some scientific popularizations. One problem with these for-the-masses books is that they present things as known fact that are in fact far removed from fact.

 

Hawkings, like many other physicists, doesn't like the idea of singularities and has been conjecturing ways around them. It is, however, just that: conjecture. (Then again, so is the SciAm article that is the subject of this thread.)

 

If Hawkings is currently the best in cosmological physics at the moment, cosmological physics is in a big heap of trouble. Hawkings has a huge handicap, and no I am not talking about ALS. His huge handicap is a very common ailment, and is one that no scientist has ever been able to overcome: He is old. Old physicists (and by old, I mean over 45) do not make meaningful contributions to the body of physics.

 

 

We cannot apply quantum mechanics all the way back to the beginning of time. To do that we would need a theory that weds quantum mechanics and gravity. This grand unification theory currently does not exist. Different groups of people are taking different routes to get to that theory, but none of them have achieved it (yet).

[Tsadi]

General relativity says singularities exist. General relativity is the best model of spacetime we have. Some even more bizarre things than singularities (e.g., wormholes) might arise, but saying they are fact is just wrong. They are purely conjectural. You appear to be young and you appear to have read some scientific popularizations. One problem with these for-the-masses books is that they present things as known fact that are in fact far removed from fact.

 

Hawkings, like many other physicists, doesn't like the idea of singularities and has been conjecturing ways around them. It is, however, just that: conjecture. (Then again, so is the SciAm article that is the subject of this thread.)

 

If Hawkings is currently the best in cosmological physics at the moment, cosmological physics is in a big heap of trouble. Hawkings has a huge handicap, and no I am not talking about ALS. His huge handicap is a very common ailment, and is one that no scientist has ever been able to overcome: He is old. Old physicists (and by old, I mean over 45) do not make meaningful contributions to the body of physics.

 

 

We cannot apply quantum mechanics all the way back to the beginning of time. To do that we would need a theory that weds quantum mechanics and gravity. This grand unification theory currently does not exist. Different groups of people are taking different routes to get to that theory, but none of them have achieved it (yet).

 

Oh, i now see the problem. You are believing i was insighting as gospal. I certainly wasn't, and i apologize if my post came across that way.

 

The post was actually there to show that we do have other arena's we can follow, without the worry (or constant worry), that the laws of physics are somehow not the same in every direction. This statement alone, as you will know, is based purely on the fact if singularities do exist, then the laws of physics certainly break down in certain area's of the universe.

 

As for Doctor Hawking's age, i agree, age can certainly take the juice out of you. I am young, as you guessed. I'm still within my education of sciences, but i am still allowed my conjecture. In the end, i seriously don't think wedding quantum mechanics and relativity together into a single framework will be enough. In fact, i would be surprised if a grand unification theory can ever be achieved at all. There are simply too many variables, and probable chaotic systems to deal with any absolute theory in general.

 

As for the books, i tend to shy away from talking about popularized science. I tend to base what i know from (either learning it in class), or by reading scientific papers. In the end, i don't like singular regions, because i simply won't accept a totally lawless region of spacetime. I think any appearance of a singularity in our work, is just the equations gone wrong.

[Martin]

i tend to shy away from talking about popularized science. I tend to base what i know from (either learning it in class), or by reading scientific papers.

I am glad to hear this! Let us move this thread from a highly popularized SciAm piece by Bojowald to a serious scientific paper by him on essentially the same topic.

 

The issue in this paper is TESTING nonsingular quantum cosmology models.

You Tsadi may possibly be interested in this because of what you say about not liking singularities when they occur in a theory's picture of spacetime.

 

In the end, i don't like singular regions, because i simply won't accept a totally lawless region of spacetime. I think any appearance of a singularity in our work, is just the equations gone wrong.

 

As we know, there is a lot of research these days into nonsingular QC, especially bounce models, and the absolutely crucial issue is testing. How to take a QC model and derive predictions from it about structure formation in the early universe.

 

That is structure formation that we have not seen yet but will see starting in 2009 when new instruments go into operation. This will be a critical test for bounce QC. Can predictions be derived and will they be confirmed?

 

So this is what Bojowald and a number of co-workers are focusing on right now and if we want to follow what is going on we should get caught up on it.

So I want to continue this thread by getting into detail about the new instruments whose launch is scheduled for April 2009, and the relevant papers by Bojowald and others.

==============================================

 

Here is some stuff on the Planck and Herschel observatories:

Both Planck and Herschel will be at L2 orbits. They will be stay 1.5 million km from the earth, out further from the sun than the earth is, oscillating around the L2 point. Both will be launched by the same Arianne rocket.

 

Here is a website of the ESA (Euro Space Agency) about Planck:

 

http://www.rssd.esa.int/index.php?project=Planck

here are some links to science goals and specs

http://www.rssd.esa.int/index.php?project=PLANCK&page=science_top

this gives detailed specs

http://www.rssd.esa.int/index.php?project=PLANCK&page=perf_top

It says Planck low frequency instrument detects 30-70 GHz and high frequency instrument detects 100-857 GHz

Lumping that together it seems like a range from 30 to 857, which is maybe where they get 0.35 mm to 10 mm

in wavelength terms.

 

Here is an ESA page and a wikipedia piece about Herschel

http://www.esa.int/esaSC/120390_index_0_m.html

http://en.wikipedia.org/wiki/Herschel_Space_Observatory

===========================

 

THE KEY RESEARCH PAPER to look at is arxiv 0808.0701

 

http://arxiv.org/abs/0808.0701

 

People in several different research lines talk with apparent confidence about quantum fluctuations seeding structure in an assumed homogeneous-isotropic universe. IMO it isn't clearly understood how inflation is supposed to have amplified and realized these fluctuations---how the shift from quantum to classical occurred and how the observed spectrum of spatial variation was determined.

There is disagreement currently, different ideas about the early universe, what could have caused inflation, what was fluctuating and how quantum fluctuations became substantive structure. There are various scenarios. So there is a good opportunity to nail some things down.

 

Quantum cosmology is specifically equipped to study this in detail, and you can see them approaching these issues in the 0808.0701 paper.

The opportunity would be to predict aspects of structure which can be looked for by Planck and Herschel satellites, when they go into operation. If they predict some details, and it turns out that way, they score cred points.

 

The earliest structure is to be seen in the CMB and in protogalaxies (galaxies just beginning to coagulate out of clouds). The detailed CMB structure in in the anisotropies, the temperature variations between small patches of the CMB sky. We are familiar with the maps from earlier surveys (COBE and WMAP). The Planck maps will be even finer detail. Herschel will have several jobs and one will be to map protogalaxy structure formation.

 

Planck will look at CMB wavelengths 0.35 mm to 10 mm.

Herschel will look at protogalaxy wavelengths possibly from 0.05 mm to 0.7 mm (I didn't find consistent information about this yet)

 

Roughly speaking the CMB is at redshift z = 1000 (more exactly 1090) and the protogalaxies are more like z = 100 (very roughly an order of magnitude less redshift, and therefore an order of magnitude shorter wavelengths).

Edited October 8, 2008 by Martin

[Tsadi]

This is very insightful.

 

Thank you.