Could Quantum Gravity Predict a Long-Distance Invariant Scale?

[marcus]

In post #55 of the A&C reference sticky
there's a link to the February WS-2004 symposium on
Quantum Gravity Phenomenology
http://ws2004.ift.uni.wroc.pl/html.html

this is about the predictions coming out of Quantum Gravity and
ongoing or planned opportunities to test.

what I have to say here is "edgy", sorry about that
a lot of cosmology these days is consensus or concordance
but this is not, it is risk-taking on Smolin's part
(and other people: Jerzy KG, Etera L, Girelli and so on)

It's looking like it could be very natural for QG to have a longdistance invariant scale L
which is on the order of 9.5 billion LY.

People who like to think in terms of "IR cutoff" and "UV cutoff" from field theory could regard this (by a stretch of analogy) as our universe's
InfraRed cutoff, just like the short length, Planck length (which is also emerging as an invariant in some QG) is our universe's UV cutoff.

I'm not suggesting we get philosophical about L = 9.5 billion LY, I only want to mention some of the coincidental information that Smolin gave in his third talk at the Winterschool symposium.

1/L² is Lambda the cosmological constant as currently determined by the supernova data---by definition of L

c²/L is an interesting acceleration. It (or more precisely
a_L=c²/6L) comes up in galaxy rotation curves. I am referring to Mondybusiness.
Mondybusiness only affects accelerations which are less than a_L
so everything is Newtonian until you get way way out and the
Newtonian acceleration a_N has dropped off to below a_L
and after that, the observed centripetal acceleration
is the geometric mean of what you Newtonianly expect namely
a_N , and the Mondy acceleration a_L.

a_{real}=\sqrt{a_L a_N}

In other words the real observed acceleration is MORE than you Newtonianly expect once it gets down very low. It is brought up slightly by geometric-mean-type averaging with what may be a constant of nature namely this a_L = c²/6L

now this clearly appears to be the work of the devil and one immediately wants to drive a stake of mistletoe thru its heart, but the damnable thing is what Smolin shows in his third paper which is a lot of snug fits with individual real galaxies' rotation curves.


and then there is the Pioneer anomaly which one hopes was just a mistake (Mother Nature has a "senior moment"?)
But it also happens when the probe has gotten far enough from the sun
so that the Newtonian sunward acceleration gets down to below a_L = c²/6L
and then the real sunward acceleration is MORE than you Newtonianly expect. It is a similar sort of thing to the galaxyrotationcurves except on a much smaller scale---but the low low threshold acceleration is comparable.

I notice a lot of people were talking about this on sci.physics.research in May, in the wake of John Baez TWF #206.
https://www.physicsforums.com/showthread.php?t=25124
but as an inveterate shunner of the edge I kept my head safely in the sand at that time. Now I am waking up to the possibility that there may be something to this conjectured longdistance scale.

some recent papers have shown how to arrange for it to look the same to different observers (thats the triply special relativity stuff that there'v been some papers about lately)

 

[John]

It is hard for most people to think in math. To have a theory based on numbers, and then fit those numbers neatly into galaxy rotation figures. I don’t know where you get the figures.

But I had this idea that space was made of points, which was a simple idea that I could describe. My idea is that space is made of points and objects travel at a consistent rate from point to point. If the points are farther apart the objects speed up. If closer together they slow down.

Think of building a sand castle on a perfectly flat beach. You take sand from the beach and it makes a dip in the beach down to the sand castle. The beach becomes a depression to the sand castle. This is how masses absorb points of space. The points are stretched farther apart by masses, and objects speed up. But in this model, way out beyond the sun or planets the points go back to being totally unstressed, just like the beach goes back to being totally flat. Though I didn’t predict it before it happened when I heard that Pioneer had slowed down, I applied my model and said, “Of course, way out there the points would be unstressed and closer together.” It would slow down. I thought maybe all my ideas are right.

All of this had been an enjoyable mental exercise. Then I read that Pioneer had slowed down when it got far away from the solar system. That fit my model and I started posting on physics websites.

Later I realized that denser space outside of galaxies would cause the arms of galaxies to bend. Now I see your post, finding it by accident, and I see this is the most cutting edge physics. Lately, I have been threatened by the administrators here, but I really may have something to offer.

 

[marcus]

... To have a theory based on numbers, and then fit those numbers neatly into galaxy rotation figures. I don’t know where you get the figures.
...

I regret to say that my response must be as follows:
I urge you to avoid taking comfort from others' example
when they themselves are sticking their necks out.

Speculation tho necessary ought to be engaged in
with cautious moderation----and rarely unless
there is there is some obvious shortcoming in conventional wisdom

Smolin and his collaborators are among the best in the gravity/cosmology research business IMHO but they are sticking their necks out on this one---it is a risky line of conjecture to be exploring.

Your post is helpful to me personally because it goads me to try to condense what I reported earlier. Maybe I can make it less mathematical, if you would like that, but mainly it should be briefer and clearer.

 

[marcus]

the first clear thing to say is a challenge
who here can recall quantitatively what the Cosmological Constant actually is?
As a quantity expressed in some units.

You remember what speed of light is-----300 thousand kilometers a second.

Well Lambda is just as important to us as that, in its own way. All the big anthropic flap reminds us that if Lambda were a little bigger or smaller than it is then galaxies wouldn't exist. A stringtheorizer Douglas has started calling anthropic by a silly new name "galactothropic"----but it is all about the Cosmological constant. we need it to be very close to what it is, just so galaxies can exist and the universe have a nice long lifetime.
Anyway that's what people (e.g. Steven Weinberg) say.

And apart from whether it is essential to existence it is also interesting because it's what makes expansion accelerate slightly. When people do a change of units they get an energy density and call it by the fascinating name of "dark energy". So we ought to know what the Cosmological Constant is quantitatively like we know the speed of light. But most people dont, because the units are strange and it is mindboggling small.

so the first thing is---why not know L = 9.5 billion lightyears?

then Lambda is easy because it is just inverse square of that.

you can be as skeptical as you want about the Pioneer 10 and 11 anomalous acceleration and the mondybusiness of the galaxyrotation curves, but just look at the accelerating expansion which is a key feature of standard model cosmology---you have to know Lambda.
Lamda is a curvature, which means an inverse square length.
that length is L.

 

[turbo]

Marcus, do you know if there's a transcript of Smolin's talks at the 40th Winter School. The Powerpoint-type slides are good, but I want to read the explanatory statements and extensions that accompanied them. I have searched for transcripts and have come up empty-handed.

 

[marcus]

Marcus, do you know if there's a transcript of Smolin's talks at the 40th Winter School. The Powerpoint-type slides are good, but I want to read the explanatory statements and extensions that accompanied them. I have searched for transcripts and have come up empty-handed.

I would like that too--but didnt find.

Or if there was a Smolin article somewhere else covering the same thing.

If anyone finds one please post the link!

 

[sol2]

Marcus I like the fact that you have gone back to Smolin to see how our discussions can materialize in his direction.

You call for concretization of mathematical interpretation and to do this the general concepts have to be understood from that early universe to today.

So I look forward to your perspective and sumation of what you are looking at.

Arivero should have this link you are asking for?

 

[turbo]

Here is a link to an edition of Edge with a rather long article by Lee Smolin regarding Loop Quantum Gravity. It is very basic - aimed at a general audience - and packed with insights into the state of the field.

http://www.edge.org/3rd_culture/smolin_susskind04/smolin_susskind.html

Also on this page is a point-counterpoint type challenge regarding the whether the anthropic principal can be considered "science".