Certain subsectors of the scientifically-oriented blogosphere are abuzz — abuzz, I say! — about this new presentation on Dark Energy at the Hubblesite. It’s slickly done, and worth checking out, although be warned that a deep voice redolent with mystery will commence speaking as soon as you open the page.
But Ryan Michney at Topography of Ignorance puts his finger on the important thing here, the opening teaser text:
Scientists have found an unexplained force that is changing our universe,
forcing galazies farther and farther apart,
stretching the very fabric of space faster and faster.
If unchecked, this mystery force could be the death of the universe,
tearing even its atoms apart.We call this force dark energy.
Scary! Also, wrong. Not the part about “tearing even its atoms apart,” an allusion to the Big Rip. That’s annoying, because a Big Rip is an extremely unlikely future for a universe even if it is dominated by dark energy, yet people can’t stop putting the idea front and center because it’s provocative. Annoying, but not wrong.
The wrong part is referring to dark energy as a “force,” which it’s not. At least since Isaac Newton, we’ve had a pretty clear idea about the distinction between “stuff” and the forces that act on that stuff. The usual story in physics is that our ideas become increasingly general and sophisticated, and distinctions that were once clear-cut might end up being altered or completely irrelevant. However, the stuff/force distinction has continued to be useful, even as relativity has broadened our definition of “stuff” to include all forms of matter and energy. Indeed, quantum field theory implies that the ingredients of a four-dimensional universe are divided neatly into two types: fermions, which cannot pile on top of each other due to the exclusion principle, and bosons, which can. That’s extremely close to the stuff/force distinction, and indeed we tend to associate the known bosonic fields — gravity, electromagnetism, gluons, and weak vector bosons — with the “forces of nature.” Personally I like to count the Higgs boson as a fifth force rather than a new matter particle, but that’s just because I’m especially fastidious. The well-defined fermion/boson distinction is not precisely equivalent to the more casual stuff/force distinction, because relativity teaches us that the bosonic “force fields” are also sources for the forces themselves. But we think we know the difference between a force and the stuff that is acting as its source.
Anyway, that last paragraph got a bit out of control, but the point remains: you have stuff, and you have forces. And dark energy is definitely “stuff.” It’s not a new force. (There might be a force associated with it, if the dark energy is a light scalar field, but that force is so weak that it’s not been detected, and certainly isn’t responsible for the acceleration of the universe.) In fact, the relevant force is a pretty old one — gravity! Cosmologists consider all kinds of crazy ideas in their efforts to account for dark energy, but in all the sensible theories I’ve heard of, it’s gravity that is the operative force. The dark energy is causing a gravitational field, and an interesting kind of field that causes distant objects to appear to accelerate away from us rather than toward us, but it’s definitely gravity that is doing the forcing here.
Is this a distinction worth making, or just something to kvetch about while we pat ourselves on the back for being smart scientists, misunderstood once again by those hacks in the PR department? I think it is worth making. One of the big obstacles to successfully explaining modern physics to a broad audience is that the English language wasn’t made with physics in mind. How could it have been, when many of the physical concepts weren’t yet invented? Sometimes we invent brand new words to describe new ideas in science, but often we re-purpose existing words to describe concepts for which they originally weren’t intended. It’s understandably confusing, and it’s the least we can do to be careful about how we use the words. One person says “there are four forces of nature…” and another says “we’ve discovered a new force, dark energy…”, and you could hardly blame someone who is paying attention for turning around and asking “Does that mean we have five forces now?” And you’d have to explain “No, we didn’t mean that…” Why not just get it right the first time?
Sometimes the re-purposed meanings are so deeply embedded that we forget they could mean anything different. Anyone who has spoken about “energy” or “dimensions” to a non-specialist audience has come across this language barrier. Just recently it was finally beaten into me how bad “dark” is for describing “dark matter” and “dark energy.” What we mean by “dark” in these cases is “completely transparent to light.” To your average non-physicist, it turns out, “dark” might mean “completely absorbs light.” Which is the opposite! Who knew? That’s why I prefer calling it “smooth tension,” which sounds more Barry White than Public Enemy.
What I would really like to get rid of is any discussion of “negative pressure.” The important thing about dark energy is that it’s persistent — the density (energy per cubic centimeter) remains roughly constant, even as the universe expands. Therefore, according to general relativity, it imparts a perpetual impulse to the expansion of the universe, not one that gradually dilutes away. A constant density leads to a constant expansion rate, which means that the time it takes the universe to double in size is a constant. But if the universe doubles in size every ten billion years or so, what we see is distant galaxies acceleratating away — first they are X parsecs away, then they are 2X parsecs away, then 4X parsecs away, then 8X, etc. The distance grows faster and faster, which we observe as acceleration.
That all makes a sort of sense, and never once did we mention “negative pressure.” But it’s nevertheless true that, in general relativity, there is a relationship between the pressure of a substance and the rate at which its density dilutes away as the universe expands: the more (positive) pressure, the faster it dilutes away. To indulge in a bit of equationry, imagine that the energy density dilutes away as a function of the scale factor as R-n. So for matter, whose density just goes down as the volume goes up, n=3. For a cosmological constant, which doesn’t dilute away at all, n=0. Now let’s call the ratio of the pressure to the density w, so that matter (which has no pressure) has w=0 and the cosmological constant (with pressure equal and opposite to its density) has w=-1. In fact, there is a perfectly lockstep relation between the two quantities:
n = 3(w + 1).
Measuring, or putting limits on, one quantity is precisely equivalent to the other; it’s just a matter of your own preferences how you might want to cast your results.
To me, the parameter n describing how the density evolves is easy to understand and has a straightforward relationship to how the universe expands, which is what we are actually measuring. The parameter w describing the relationship of pressure to energy density is a bit abstract. Certainly, if you haven’t studied general relativity, it’s not at all clear why the pressure should have anything to do with how the universe expands. (Although it does, of course; we’re not debating right and wrong, just how to most clearly translate the physics into English.) But talking about negative pressure is a quick and dirty way to convey the illusion of understanding. The usual legerdemain goes like this: “Gravity feels both energy density and pressure. So negative pressure is kind of like anti-gravity, pushing things apart rather than pulling them together.” Which is completely true, as far as it goes. But if you think about it just a little bit, you start asking what the effect of a “negative pressure” should really be. Doesn’t ordinary positive pressure, after all, tend to push things apart? So shouldn’t negative pressure pull them together? Then you have to apologize and explain that the actual force of this negative pressure can’t be felt at all, since it’s equal in magnitude in every direction, and it’s only the indirect gravitational effect of the negative pressure that is being measured. All true, but not nearly as enlightening as leaving the concept behind altogether.
But I fear we are stuck with it. Cosmologists talk about negative pressure and w all the time, even though it’s confusing and ultimately not what we are measuring anyway. Once I put into motion my nefarious scheme to overthrow the scientific establishment and have myself crowned Emperor of Cosmology, rest assured that instituting a sensible system of nomenclature will be one of my very first acts as sovereign.
Some of these criticisms might be applicable to physics. Often what happens is that radically different physics amounts to appealing to completely different modes of thought. In my small way I at least attempt to think this way by seeing general relativity and quantum mechanics as relationship systems between particles.
Maybe our whole society needs that sort of boot, that is unless we are to tread a sorry road laid out by Bush/Cheney — a road that will lead us to some sort of totalitarianism. Yet a precursor for such changes are usually seen in the artistic and intellectual fields. Usually such changes are preceeded by new forms of art and music or new intellectual ideas. Unfortunately music and art are pretty much in the nadir right now as I see it.
Lawrence B. Crowell
LC,
I have been reading your research and am really impressed! Best wishes in your continuing responsibilities both re field work and in the classroom. I’ll continue to follow your work…you have many interesting ideas in a subject area, an understanding of which is, I believe, critical to a proper understanding of cosmology.
The wacky, quirky, and sometimes revolting nature of existence, is powerful evidence, I believe, that the development of information, order and intelligence in the universe, as basically awesome as it is, originated internally within the archaic universe an eternity ago, according to some process resembling the natural selection of organic evolution we observe here on Earth over the eras and epochs of the development of existing life terrestrially.
You really are interested in that process! It is tempting to speak about “origins” in a universe where such a word is cosmologically meaningless…as meaningless as asking where the original energy “came from”. As finite humans we simply cannot conceive of eternity…even in our imagination! I think it is best, for scientific purposes, to regard eternity as a kind of (very gradually changing) horizon.
However, just as on the lifeless early Earth, we can justifiably assume there was a time in the eternal past when quantum randomness was everywhere and information was nowhere. Because of a universal atemporal nature, frame invariance and a very specific energy density, however, it was possible for different quantum conditions to develop at different frames- and remain that way- conserved.
As the quantum conditions at different frames interacted, certain types of information became dominant and pervasive in the universe, to the exclusion of other types of quantum states. Initially this process resulted in sets of classical particles, then baryonic matter in certain proportions…and eventually eternal “knots” of complexity related to each other in their origin and existence and continuing development of diverse observational capacity. These gradually evolved to the level of complexity we observe today.
JM,
It is funny how the passage of time usually results in great advances in knowledge, but the old ideas keep re-surfacing- with important modifications.
Relativity is, in many ways Platonic and likewise reflects in some crude ways the observer centered universe of Ptolomy. Yet Platonism while based on periodicity, is completely static in concept, and we can be sure that change DOES occur in the universe, even if we do not observe change in the way it actually occurs cosmologically. The fact that time and change exist at all is a hint as to the finitude of universal mass and spatial extent. I don’t agree with Mach on everything, but he made many, I believe irrefutable cosmological points.
LC,
I have a biology background but have taught HS physics, physical science, geometry, trigonometry. I posted some conceptual material on the internet 10 years ago and was contacted by UNC Chapel Hill and asked to continue my conceptualizing of their website for a while. I have studied relativity since 1967. While overseas, with no TV or other distractions around, I ordered materials and focused on the subject. The site is archived material and some of the earliest is not particularly accurate, however it has been a work in progress. Some professors have had their undergraduate physics students read it, and I have been contacted by a number of researchers and theorists.
Ned Wright expressed inital friendly support for the project as did RM Kiehn from the University of Houston. Dr. Kiehn took the time to read extensively on the site and graciously commented that it was “off in a few details”. From what I have continued to learn, I realize now how gracious the good Doctor was! However, both Ned and Dr. Kiehn are just fabulous teachers and they, as good teachers, know the importance of encouraging their students. I myself have spent 24 very rewarding years in the classroom…rewarding partly as a result of benefiting myself from that kind of mentoring!
This is really a great blog! You all are to be commended!
Sam Cox
Lawrence,
To the extent it is a cycle, there is ascent and descent. Economically, politically and religiously, we seem to be at the top and headed down. Sometimes it’s prelude to crashing at the bottom and sometimes it’s creating energy for the next climb.
With expanding energy and collapsing mass, the secret is to have enough energy to keep the structure expanding. The problem is that the larger the structure gets, the more energy it takes to keep growing. Eventually the weight exceeds the input and it starts collapsing. Call it the physics of institutions. The bigger they get, the harder they fall.
Sam,
It’s good to feel you have something to give.
This is the only writing I’ve had published anywhere that got some amount of feedback;
http://www.exterminatingangel.com/index.php?option=com_content&task=view&id=203&Itemid=118
I met R. Kiehn at a conferece some time ago, maybe 8 years go or so.
He’s the guy with the nonlinear soliton stuff as I recall.
Some sort of change is likely to occur with quantum gravity. I think that gravitation and quantum mechanics are systems of relationships between particles. I have indicated some on how I think that works, but it goes into considerable depth on lie algebraic systems and quantum codes, lattices and the like. I intend to get a web site up in a few months on this, and have actually written most of the web pages already. I call one group of them climbing up heterotopia to AdS/CFT. Another chunk involves a lot of work on the preservation of quantum information and how certain quantum codes, Golay codes on the sporadic M_{24} and Leech lattices. This stuff actually gets infernally mathematical, but in order to express a unification of these “relationships” there appears to be no escape from this.
Lawrence B. Crowell
Lawrence,
The problem isn’t with the math. The problem is the assumption that the math is the reality, rather then a model of reality.
If you want some outside perspective on this, look at what the financial markets have become, relative to the economy they are based on and supposed to be a tool for.
This is diverging from cosmology and physics, but honestly I don’t have too many cares about anything which involves “institutional physics.” If I had to sum it all up, the human species is some sort of terminator species that is turning everything it can consume into garbage. It is just that we also happen to be at least locally cosmological observers. Our future tenure is likely to be rather brief, certainly on cosmological or geological time scales. So we are faced with the question of whether we can figure out the nature of the universe within an unknown, but likely very short, time we have left.
I think it is a problem with all intelligent life, at least as defined by the ability to abstract concepts, to communicate them in some linguistic system and finally to have the physical attributes required to configure their world according to such concepts. In other words in the case of human beings this involves brains, tongues and hands. Once that gets going, and I suspect that with Homo erectus this crossed the rubicon to intelligent beingness with learning to manipulate fire — the gift of Promethius.
Once that happens an intelligent life form of this type is no longer constrained by its environment. Given any such constraint imposed on intelligent beings they are able to figure a way around it. This then means that a cardinal rule of biological communities or ecosystems is broken: Species of life are regulated by their interactions with the broader community of life. As a result we humans number 6.6 billion currently, and at no time in the history of life on this planet has there numbered this many animals of our size and dietary requirements at once. Then compound this by our 100 fold increase in energy and resource demands, and not to mention our entropy impact in the form of pollution and environmental degradation. Step outside, or drive around and look at it all — it’s exceedingly extraordinary. Some of our fabricated stuff is in space, even some on the moon with booted footprints — astounding!
I suspect this is a problem with all intelligent life, though we humans have some additional properties that hot-wire us, such as we do not have sexual seasons as with other animals — we “do it” all the time and have babies like large rabbits. The SETI conjecture is that we are not alone, and in the universe in total this is probably correct. Yet I suspect that intelligent life is very rare and may prove impossible to detect in the universe, for it needs to be close enough for us to detect.
The role of intelligent life in the universe is then an interesting one. I suspect in most if not all cases it is transient. Intelligent life might then observe the universe and if they persist long enough, maybe they are not so wreckless with their nuclear firecrackers or they are sufficiently limited in their appetites for consumption, they understand the universe up to some limit (what ever that is) of knowability. Maybe there is some ensemble of possible intelligent life forms, and we humans are just one of the experimental cases in the sample space. On the other hand, maybe we are indeed the only ones in the whole thing — and we are a two legged locust swarm tearing down the life support system on our planet or “spaceship.”
I am not a fan of so called Anthropic Cosmological Principles (ACP), though I think the weak ACP does raise questions. Clearly the universe is configured as “such as such” in order for us to exist. However, I think that there is some comsological einselection process, some system of decoherent processes that reduce the overlap between possible cosmological states D(Psi, Psi’) —> 0 which selects for an extremization of local complexity. Intelligent life might then just be a specific example of this, and maybe ultimately some sort of fluke in this outcome. This has a sort of Leibniz-esque element to it, for it echos his “best of all possible worlds” thesis. So maybe the grand path integral for all possible quantum cosmological amplitudes self-decoheres by inflationary processes so that locally classical (like) structures come about by an extremization of possible local complexity.
Lawrence B. Crowell
Lawrence,
Consider it from a biological perspective.
For one thing, consciousness, as bottom up emergent phenomena, is cause, while intelligence is top down effect. Life creates organisms in order to consume them, so what will emerge from the ashes of the monetary wildfire that is about to burn down our current abode?
To the extent life on this planet is capable of functioning as one super-organism, we might be at the embryo stage, consuming all the proteins and other nutrients within the egg before hatching. We have definitely reached the limits of what our environment can support with humanity at top predator, but after this paper bubble bursts, the only way I can see to re-constitute it is to formulate money as a public utility. Similar to a public road system. This would tie rights to responsibilities in a very coherant fashion. This would place the very basis of public wealth as a public utility. Private wealth would have to be largely a function of maintaining a healthy community and environment, because the reliance on wealth would be initially constrained and only expand as people developed faith in the public process. I went into the foundation of this situation somewhat in the link on post#203, but not the structure that might emerge from it.
Possibly humanity can be reformulated as the central nervous system of the planetary organism, not just its primary exploiter.
You’re right, this is somewhat off topic, but I’m in this discussion in the first place because I do feel that in a very fundamental way, a lot of the general confusion with life and reality goes to the very core of our philosophic assumptions. The issue of whether the absolute is an ideal from which we fell(Plato), or the essence out of which we rise(Aristotle) is still playing out, bubbling under the surface of everything from monotheism to mathematics.
LC,
“I met R. Kiehn at a conferece some time ago, maybe 8 years go or so.
He’s the guy with the nonlinear soliton stuff as I recall.”
NOTE: Outside of the concept description on the homepage of my site, the rest of the material is archival…some as much as ten years old, so some of the links do not work. However the link to Dr. Kiehn’s site, “Cartans Corner” is still live and there is some interesting recent material posted there.
Dr. Kiehn is “emeritus” and retired now, but the last I heard he is still active. He has done a lot of work with non-linear solitons as you note, and time process. He was on the team which developed thermonuclear weapons during the 50’s and spent a lot of time at Bikini and Eniwitok.
“Some sort of change is likely to occur with quantum gravity. I think that gravitation and quantum mechanics are systems of relationships between particles.”
NOTE: You are working in a very challenging area, at the lower levels of scale where GR established relationships between particles meld with the world of quantum fluctuations. GR as a description of gravity is of course, precise to very small scales. When you speak of quantum gravity, you are inferring a kind of Newtonian gravity in which universal entaglement becomes an important principle.
Just from a very rough conceptual perspective, I would think that such problems as wave/particle duaity would complicate your work. Conducting an investigation as to how information originates, is embedded (rooted), and is conserved in the sub-microscopic region between the Planck realm and particulate reality is essential to a proper understanding of what the universe is, where it came from and where it- and we- are going.
” I have indicated some on how I think that works, but it goes into considerable depth on lie algebraic systems and quantum codes, lattices and the like. I intend to get a web site up in a few months on this, and have actually written most of the web pages already. I call one group of them climbing up heterotopia to AdS/CFT. Another chunk involves a lot of work on the preservation of quantum information and how certain quantum codes, Golay codes on the sporadic M_{24} and Leech lattices. This stuff actually gets infernally mathematical, but in order to express a unification of these “relationships” there appears to be no escape from this.”
NOTE: I’ll be looking for your web site. It is one thing to roughly conceptualize this and quite another to formally reduce what we know must be true to a mathematical model which has excellent descriptive and predictive value. We know gravity has to be Newtonian- and thus quantum. We also know that because GR is scale related and is so accurate, it is probably not wrong. What we learn will only serve to enrich and extend our present knowledge.
By its very nature of course, GR is a scale related (geometric) concept and we know that quantum effects, while measurable at macroscopic scales, diminish as scale in the universe increases. We know that CPT symmetry seems ludicrous at macroscopic scales where time process becomes “obvious”, and that the reason for this must be related to the existence of scale related observational horizons of one sort or another.
We also know that once we get our complete concept of the universe as described in SR/GR/QM properly combined and mathematically formalized we will not only understand the universe better, but will lay the foundation for an unbelievable expansion of technology.
Just one final remark. Newtonian quantum gravity is really a pretty simple idea, and we know gravity has to both quantum and roughly newtonian to prevent the universe from coming unglued. I’ve taught basic probability theory, binomial expansion and related concepts in Genetics and Physics and I would think that any mathematical formalism relating to the emergence of information from the quantum realm- or, in the reverse, its appearence on 4D event horizons would be related to an involved study SR/GR relationships, set theory and lattices as you mention. I’m sure you won’t forget the time element…that different locations in the universe are not only distance, but time and observer related.
The fact that the universe is what the observer observes, and the universe can be observed in an almost infinite variety of ways, will make your job more difficult.
Sam Cox,
You mention that we can’t conceive of the origins of the universe. Well, that’s the case with a lot of science which we can describe very accurately mathematically, such as quantum mechanics or extra dimensions. The inability to intuitively understand something does not indicate an inability to describe that something. Science has basically been nothing but a long process of moving past our own limitations in understanding to better describe the world around us. There is no reason yet to suspect that we won’t be able to go all the way back and say something definitive about the beginnings (if there were any), or the ultimate nature of the universe. The best we can say now is that we don’t yet know how much we will be able to discover.
If we can look further into the distant unvierse we should be able to understand the big bang. Already the anisotropy of the cosmic microwave background is revealing much. With gravity wave detectors and neutrino astronomy we might be able to observe much further back to near the earliest moments of the universe. Depending upon how science policy plays out in this nation or other nations it is possible that in the next 50 years we may actually be getting data from the ultimate scattering experiment — the big bang. With that we might be able to support quantum gravity/cosmology theories with real data.
An important aspect of physics is triality. An example would be with the family structure of elementary particles. The weak interactions is likely an su(2) + su(2) theory for left and right fields. Due to CP violations our low energy universe is just the left handed part. Now this is so(4), if you are familiar with group theory stuff. Gravity is so(3,1) and this with the weak interactions is so(7,1) = so(3,1) + so(4). This may be extended to the exceptional group f_4 if we add in the short roots 8 + 8′ + 8″
f_4 = so(7,1) + 8 + 8′ + 8″,
and these additional roots are the particles (e,nu_e), (mu, nu_mu), (tau,nu_tau) for the leptons. This is a triality structure, and what this exceptional group does is to put the Grassmannian (Fermionic) fields on the same frame bundle with the gauge fields.
This can be carried to the exceptional group E_8 with QCD as,
e_8 = f_4 + g_2 + 26×7,
where the “26” is the Jordan algebra J^3(O) over the octonions. The “26” is the bosonic string. In a more general setting there are three of these E_8’s: one the chiral dual to the first E_8 and the third an exceptional group required to define homeomorphisms over all four-manifolds that are configuration variables for quantum gravity states. This gets into some very abstract mathematics, but from these three is the Mathieu sporadic group m_{24} which is the quantum code I am working towards.
Lawrence B. Crowell
I was going to write a further ending to this. The e_8 group contains string theoretic information. Yet the requirement for there being three E_8’s, an additional one to the E_8xE_8 of the heterotic string theory, is due to a quantum constraint problem, how wave function(al)s over metric configuration variables correspond to classical spacetimes, and a matter of general covariance. This portion ties heavily to the Loop Quantum Gravity (LQG) approach. String theory appears to be a vast theory of many possibilities, while LQG is more of a constraint theory. Indeed LQG is a theory of constraint conditions on the action.
String theory and LQG appear to be different views of quantum gravity, as if one were looking into the same room through different keyholes in separate doors. Of course there are certain “battle lines” between these two approaches to quantum gravity, and unfortunately there seems to be a bit of pride on both sides which appears to be drawing up a growing wall between them.
Lawrence B. Crowell
LC,
“This portion ties heavily to the Loop Quantum Gravity (LQG) approach. String theory appears to be a vast theory of many possibilities, while LQG is more of a constraint theory. Indeed LQG is a theory of constraint conditions on the action.”
NOTE: I’ve read up on string theory, but in a general kind of way have come to regard “strings” as pretty much of a 4D frame of reference way of describing the quantum realm, not well enough constrained…not enough anyway to logically lead to a universe filled with informational complexity. I’m still open…thats just a general reaction.
LQG is something else again. I mentioned elsewhere on the blog the recent work at Fermi, an actual discovery, that certain types of mesons occillate between matter and antimatter at a regular and predictable rate…2.8 trillion cycles per second. Although Fermi is not dogmatic about it, since this occillation actually occurs at the quark level, there may be a similar, general occillation of the baryonic universe as a whole at the quark level, expalining “where the antimatter has gone”- by implication, nowhere. At our level of scale we observe one side only- there is a horizon involved. This has implications about the very nature of black holes and white holes, the nature of time as this “pulse” relates to the gravitational time dilation relationship and so on.
LQG seems to me at first glance to fit better with a concept of gravity-and the quantum (Planck) realm in general- which is better organized foundationally and less inherently random…more in line with Fermi’s recent discoveries of matter-antimatter occillations at the quark level.
LQG also seems to me to fit nicely with the GR invariant frame concept…which provides a logical mechanism for the development, preservation, and possible inter-relating of information…inorganic and organic evolution.
I don’t personally understand why battle lines need to be drawn, but I guess when people devote a lot of time to their work they have a certain (I believe) unnecessary emotional investment in the outcome. We forget that the universe just “is”…it does not “care” what Sam Cox- or anybody else, for that matter, thinks. Anyway, as the songwriter said; “Fame if you win it, comes and goes in a minute”!
One thing about the universe I really like is that it has this “feral” quality about it. On the one hand it is “domesticated” in the sense that it seems to operate according to a well coordinated set of principles and should I say, by LQG “constraints”? On the other hand, the universe can, in a way that sends chills down my spine, be a wild and very demanding place in which to exist.
I don’t think that being too “sheltered” is really the way to live, yet mankind and all mammals must give a measure of protection to their young- or they wouldn’t survive to adulthood!
However, being exposed to almost constant danger and challenge has really “made” my life. I grew up in a tough neighborhood and became “street-wise” in a hurry. I attended camps where we cooked over fires and showered in cold water. Later, I matured in a thatched roofed South Pacific mens house, fought off sharks as we netted fish, was exposed to just about every disease known to man, and survived a rogue wave which crashed over us guys as we slept on the hold of a ship. That’s just for starters!…but that is the universe I know, and have been very close to since I was a kid. Yet it is not just the danger and challenge of the universe which makes it what it “is”. I have known the power of the love, loyalty and devotion of family and friends…foxhole friendship too!
The link between observation, experience and existence truly makes us what we are!
JD,
I think your comments were very appropriate. In the end, just as in the case of the human exploration of the planet, theoretical horizons like “eternity” may turn out to be completely- and easily- inderstandable. In fact, these “horizons” may not really turn out to be horizons at all…we may recognize eternity for example, to really be a part of ourselves!
Sam Cox
An additional thought…
a rather obvious additional thought. There are important constraints built into probability theory, as binomial expansion for example. We usually use repeating, periodic events and or sets of events in our evaluation, as heads/tails, boy/girl. When we evaluate quantum behaviour some analogous periodic phenomena of restricted character are being evaluated. To my mind, this kind of mathematical structure foundational to QM, also implies duality, periodicity and implicit structural constraints…structure, lattices, scale, certain kinds of invariance etc and is therefore most consistent with LQG….
LC,
…I also illustrated for my students in classroom experiments, how dimensionality is implicit in many probablility studies- and if that dimensionality varies even slightly, the results of our experiments are drastically altered. For example, if we use nickels instead of pennies in a coin toss, the nickel may actually land on its third side, and the wider the coin, the greater the chance of this additional event occuring.
You are working in an area where dimensionality is just appearing as a characteristic of the universe, and that would seem to me to be a complicating factor in your work. Fortunately, in terms of orders of magnitude, the region between 10 to the minus 36th Cm and 10 to the minus 12th Cm. or so is vast, but relativistic effects will make your task more challenging…and relativistic effects dominate in that part of the universe!
Relativisitic effects which are seemingly so easy to describe as “reality” when remotely observed from our frame, can be expected to become a horse of a different color when the scale of observation is reduced.
Sam,
Periodicity, duality, etc. is one side of a larger duality, in which the two sides define a larger whole and the cycle is part of a larger process. It takes many forms and relationships. Walking along involves many discrete steps, but it also involves a constant motion. Order and chaos describe complexity. Inside and outside define a set. To the extent physics is largely premised on making measurements, it’s focused on the particles and not the space inbetween, which seems to be dismissed as completely defined and dependent in these perimeters, but what if it is the other way around; the field creates the particles, even though it’s the particles which define the field.
Think of it in terms of the eco-system and the organisms inhabiting it. Generally we accept that form follows function, but it seems that in physics, we can only measure form, so it’s assumed function is the consequence, not the cause.
Sam,
Your last post seems to cover the point I was making.
Loop Quantum Gravity is more honest with general relativity. It is a “space plus time” spinor theory of relativity which quantizes certain connection coefficients. There are a lot of details, but it essentially is a theory with the action
S = NH + N_iH^i + B*Q + ….,
where N is the lagrange multiplier for the Hamiltonian N_i the shift or momentum lagrange multiplier and so forth. This action enters into a path integral
Z = int &g exp(iS),
which determines the field amplitudes. These are all constraints which define the dynamics on a contact manifold. It has no background dependencies and so forth.
String theory is a bit more problematic with gravitation in some ways. In particular a string on the spacetime metric has “vibrations” which on a scale larger than the string give curvature corrections on a background metric. This runs into trouble with general covariance and coordinate independence. However, there are some nuggets of gold due to this as well, particularly this indicates something about the nature of four manifolds as configuration variables of quantum states.
Lawrence B. Crowell
Lawrence,
Since most of what you say goes way over my head, I can’t figure out if you addressed my query in #195(unless it was the first paragraph of #199).
It was that you describe light being stretched out as it falls into a gravity well. This would seem to mean that it is redshifted falling in, as well as climbing out. I’m repeating the question because the conclusion I drew from it seemed a bit too simple and obvious that I must be missing something;
It would seem easy to disprove this by observation, since light passing close to the sun or some other star would be neutralized if it is blueshifted falling and redshifted by an equal amount climbing out, but if the light is being stretched out as it fell in and stretched as it climbed out, there would be an overall redshift from this passage. What am I missing?
Light as measured by an observer on the surface of a gravitating body would be blueshifted (compressed), while it is redshifted as measured by an observer watchiing photons emitted from the surface of a gravitating body.
A gravity field acts a bit like a lens to photons. A regions with spacetime curvature can be modelled as if it had a spatial variation in the index of refraction. Just as light passes through an ideal lens with no loss and with the same wavelength the same happens to photons which pass through a region of spacetime curvature. Large elliptical galaxies act as “Einstein lenses” which give a distorted image of more distant galaxies.
Lawrence B. Crowell
It’s blueshifted as it falls in, and redshifted as it comes out. Now, there’s a slight change due to the expansion of the universe from non-matter components (e.g. dark energy), dubbed the Integrated Sachs-Wolfe effect (ISW effect), as the expansion of the universe over the time the light traverses the potential, if that expansion is driven by more than just normal matter, causes the potential to change during the traversal. With a cosmological constant, for instance, the potential becomes shallower as the light traverses it, so the blueshifting as it goes in outpaces the redshifting as it comes out, making for a small blueshifting of the light as it passes through overdense regions, and a small redshifting as it passes through underdense regions.
This, however, is quite a small effect, and the overall redshift that we see in far-away galaxies is predominantly due to the expansion of the universe, which also stretches the wavelength of the light as it travels. So, for example, if a light beam was emitted when the scale factor of the universe was 1/100th its current value, then the wavelength will now be 100 times longer than when it was emitted (neglecting the small ISW effect above).
Right, and the largest effect is that the light path can be bent or deflected to distort the image behind the gravitating body. Yet the wave length of the photon at “-infinity” is equal to that at “infinity,” where these are defined as asymptotic regions. This of course ignores comsological expansion and other matters, so the “infinity” is a bit more local — but it is good enough FAPP.
Lawrence B. Crowell
Lawrence,
I suppose it would be essentially whiteshifted(?), since the light is traveling at the speed of light, so there would be no signal preceding it, that would be blueshifted by its approach. I guess the stretching out you described would be meaningless to an observer on the surface, as all the lightwaves hit at once. Sort of like a sonic boom is caused by all the sound waves being compressed. together.
Not only do gravitational lenses distort the path of the light, but they apparently magnify it as well. Does this have any side effect on the wave length? I ask because of your point that from the perspective of the light, gravity squeezes it, as it stretches it. Does this squeezing intensify the light and thus magnify it? For example; Shining a light through a magnifying glass intensifies it, as it compresses it to a point. Does it affect the frequency of the light waves by stretching them, as it compresses the area of focus?
Jason,
If it is stretching the wavelength “as it travels,” this would seem to be a local effect. So why does the speed of light remain the same? As you describe it, the very fabric of space is being stretched, yet the speed of light remains constant to a dimension of space that does not stretch.?
Whiteshifted makes no sense. Just like any other particle, as a photon enters a potential well, it gains energy. For a photon this means that its frequency increases/wavelength decreases, hence it is blueshifted (the speed doesn’t change, for obvious reasons).
Yup, it’s a local effect. No, the speed doesn’t change. The important thing to note here is that speed itself is only well-defined locally. The expansion of the universe greatly affects how long it takes for a light beam to get from point A to point B (if A and B are far enough apart for the expansion to make a difference), but at every step along the way it’s only ever traveling at the speed of light.
A lens diverts the path of light by definition. It may magnify an image, and gravitaitonal lenses has a magnification effect, though with a high degree of distortion.
A gravitational lens has no effect on wavelength. I went to a hotspring yesterday, one you have to hike into a ways. On the bottom of the pool the light illuminated with the usual caustics randomly wiggling around. Around these caustics were little “fringes” of red and blue. Most optical media have an index of refraction that depends on the frequency of light
eps = eps(freq)
which causes this chromatic abberation. This is a problem for the lens designer and optician. The gravitational lens has no chromatic abberation! If it did then it would mean geodesic motion depended upon inertial mass in a way which violated the equivalence principle and the equivalence of inertial and graviational mass.
On a flat background the overall change in wave length is zero. If the background is expanding so there is a gravitational physics comoving frames apart (points on the space are sliding away from each other) there will then be an added redshift of light. This is of course what is observed, and further this comoving of frames away from each other is accelerating.
Lawrence B. Crowell