Greetings from Paris! Just checking in to do a bit of self-promotion, from which no blog-vacation could possibly keep me. I’ve written an article in this month’s Scientific American about the arrow of time and cosmology. It’s available for free online; the given title is “Does Time Run Backward in Other Universes?”, which wasn’t my choice, but these happenings are team events.
As a teaser, here is a timeline of the history of the universe according to the standard cosmology:
- Space is empty, featuring nothing but a tiny amount of vacuum energy and an occasional long-wavelength particle formed via fluctuations of the quantum fields that suffuse space.
- High-intensity radiation suddenly sweeps in from across the universe, in a spherical pattern focused on a point in space. When the radiation collects at that point, a “white hole” is formed.
- The white hole gradually grows to billions of times the mass of the sun, through accretion of additional radiation of ever decreasing temperature.
- Other white holes begin to approach from billions of light-years away. They form a homogeneous distribution, all slowly moving toward one another.
- The white holes begin to lose mass by ejecting gas, dust and radiation into the surrounding environment.
- The gas and dust occasionally implode to form stars, which spread themselves into galaxies surrounding the white holes.
- Like the white holes before them, these stars receive inwardly directed radiation. They use the energy from this radiation to convert heavy elements into lighter ones.
- Stars disperse into gas, which gradually smooths itself out through space; matter as a whole continues to move together and grow more dense.
- The universe becomes ever hotter and denser, eventually contracting all the way to a big crunch.
Despite appearances, this really is just the standard cosmology, not some fairy tale. I just chose to tell it from the point of view of a time coordinate that is oriented in the opposite direction from the one we usually use. Given that the laws of physics are reversible, this choice is just as legitimate as the usual one; nevertheless, one must admit that the story told this way seems rather unlikely. So why does the universe evolve this way? That’s the big mystery, of course.
By the way, I recently found this very nice quote from no less a personage than Brian Greene [Fabric of the Cosmos, page 164]
“High entropy is the natural state of being. You should never be surprised by or feel the need to explain why any physical system is in a high-entropy state.”
From this it follows, of course, that the natural way for the universe to be born was in a high-entropy state. But it wasn’t……..
This whole discussion — the arrow of time reversed, galaxies formed out of white holes, eggs spontaneously unscrambled in a way that respects chicken anatomy and the (d)evolution of life on earth — reminds me of a TV cartoon show in which some people try eating with the wrong end of their digestive tract.
Doug,
Most objective physicists prefer to ignore the concept of “now” because it cannot be defined without referencing your own consciousness (that doesn’t necessarily mean they’re right). There is no other other standard to determine what “now” is (what would “now” be when you’re dead?). Even Einstein did not think that a theory of the present was ever possible – relativity is a theory of possible “nows”, but not an actual “now”. And since “now” divides the past and the future, then the past and the future can also not be defined without referencing your own consciousness. Personally, I think they may be making a big mistake, but I don’t know how else they could proceed, objectively. “Now” is fundamental to time and reality. Something about “now” and consciousness are inextricably intertwined – more so than “here”, IMO.
Doug,
Most objective physicists prefer to ignore the concept of “now” because it cannot be defined without referencing your own consciousness (that doesn’t necessarily mean they’re right). There is no other other standard to determine what “now” is (what would “now” be when you’re dead?). Even Einstein did not think that a theory of the present was ever possible. Relativity is a theory of possible “nows”, but not an actual “now”. And since “now” divides the past and the future, then the past and the future can also not be defined without referencing your own consciousness. Personally, I think physicists may be ignoring something important, but I don’t know how else they could proceed objectively. “Now” is fundamental to time and reality. Something about “now” and consciousness are inextricably intertwined – more so than “here”, IMO.
Here’s the thing I’m not quite getting about Sean’s argument, though. He seems to be drawing no distinction between the microstates possible in the early universe and those possible today. In fact, he explicitly states that there is no such distinction, that the number of microstates available simply doesn’t change.
I don’t understand how this can be possible. I mean, if we consider a universe with nothing but a cosmological constant (a fair approximation to the earliest epoch of our universe of which we are aware), then what lies within a cosmological constant is essentially constant with time. All descriptions of that space just don’t change as time goes on. So it stands to reason, I should think, that the number of possible microstates within a given cosmological horizon also do not change with time as this region of space expands.
However, it is expanding. So though the possible microstates within a region are not changing, the total volume that expands from a particular region should have a number of possible microstates that increase with volume. So would not the number of possible microstates necessarily increase with the expansion of the universe? Would this not mean that inflation has at least a role to play in explaining why the entropy of our early universe was so low? I mean, by allowing a universe such as our own to come from so small a state should mean that the earliest part of our universe, though much lower in entropy than today, was also lower in its possible maximum entropy, due to the smaller volume. Surely that has to be part of the answer, unless I’m just not understanding something.
Oops, typo. Second paragraph, second sentence should end in:
“then what lies within a cosmological horizon is essentially constant with time.
JD, I thnk you should look at SC’s paper with Chen. Look at the section about unitarity. Basically the size of a region has nothing to do with the number of degrees of freedom it contains. What changes is not the number of degrees of freedom, but rather the number of degrees that are excited out of their ground state.
James N said,
“This whole discussion — the arrow of time reversed, galaxies formed out of white holes, eggs spontaneously unscrambled in a way that respects chicken anatomy and the (d)evolution of life on earth — reminds me of a TV cartoon show in which some people try eating with the wrong end of their digestive tract.”
Hi, Enjoyed your comments very much! Geometric inversion is a very interesting phenomenon, and would not at all necessarily result in a universe of the ludicrous kind we would imagine from our frame of reference…observing particulate 4D event horizon surfaces at the edge of the singular.
“galaxies formed out of white holes”…seems strange, but what are we investigating when we analyze the CBM? The existence of a “big bang” and our origins from same are experimentally valid conclusions we can draw from the universe we observe.
When we move from culture to culture we are stunned by the incongruity of what seems “normal” to other folks.
Eggs unscrambling seems crazy from our frame. So does doing our business and eating in reverse. An advantage of such a universe is that it is “safe”. A disadvantage is that we become more childlike.
It took some time for us to adjust to these present conditions…we needed mentoring to survive. We might not need mentoring on the other side, in fact we wouldn’t need mentoring on the other side, but observing a 4D cross section of the universe in decreasing thermal and increasing informational entropy sure would take some “getting used to”!
I thought the article was a great read, and it cleared up a few points for me while introducing some perplexing new ones (such as a distinction between virtual particles and those which fluctuate in and out of brief existence – Huh?! I thought these were one and the same, but evidently not).
Perhaps experts critical of speculation beyond the realms of experiment (for now) should remember that the average SA reader, especially keen young future scientists, are inspired by mysteries and reassured that not everything is known, as the average college textbook would have us believe. Why bother pursuing a career in science if they can’t contribute? Isn’t that why those experts started?
Clearly the central mystery Sean addressed was how the Universe can start in a state of low entropy when the number of microstates remains unchanged over time.
In the context or “framing” of pre-bang evolution, which is widely accepted these days not least by Sean as he explains in the article, the only way I can make sense of the low initial entropy enigma is that the Big Bang marks a qualitative change in the types of degrees of freedom which come to the fore.
In other words, after settling into a maximum entropy state, by some means the microstates are “folded up” in regular formation so that a low-entropy dual set of microstates of comparable cardinality “comes into focus” in a sense and takes over.
For example, when a gas freezes into a crystalline solid, the molecules become locked into place in the lattice. But phonons and vibrations then become a new kind of dynamics in their own right, whereas in the gas their existence was only immanent (and no, I didn’t mis-spell “imminent”!)
As a more commonplace example, consider a squad of grenadiers, or National Guards if you’re in the US, performing a drill. One common maneuvre is for alternate lines of a rectangular squad to march about and back through the complementary lines. Looks a bit messy for a while, but when the lines are re-aligned the squad can halt, all do a left or right turn, and march off as a unit at right angles to their former direction.
I suggest the causally-connected universe can achieve an equivalent effect in the distant future, if we assume it eventually starts contracting. When the blue-shifted random background energy reaches a critical black-hole density, time in its previous measure will simply cease (in that a fictitious observer at any given point would perceive everywhere else fade away to nothing, so the local temperature would also become everywhere zero).
At that point (God knows how, but probably by something like a Fourier transform) time and temperature get switched, as do mass and energy, and the emergent dual universe starts inflating fast even as the old contracts slowly – Everything is ass over tit, or inverted, which makes it uncommonly hard to gain a clear intuition as to how it works.
Note that the new universe doesn’t “bud off” the old. It is inherent in the old, which still in a sense exists, like those clever pictures that show a bowl of flowers and at the same time an old guy’s face. That’s what duality means – an alternative consistent view of the same whole.
What’s more, if we also assume this scenario is periodic, so there’s a kind of ping-pong alternating dual evolution analogous to EM radiation, then perhaps it could be verified *experimentally*. It may be that periodicity imposes some constraints on physical constants such as the Fine Structure constant.
Apologies to experts patient enough to skim beyond the first few lines of the above if any or all of it sounds nonsensical – You may need to read between the lines, and use your imagination, to guess how I *should* have expressed it!
As St Augustine wrote: “The new is in the old concealed. The old is in the new revealed”. In summary, I submit that to understand the beginning, it will greatly help if one understands the end ..
@ George Musser:
Many many thanks. I am sending you a mail.
Why suppose it takes separate universes to manifest these two directions, if they can be explained in terms of the inherent dualities of this one? Here’s a supposition; What if the philosophic basis of modern cosmolgy and physics was eastern dualism, rather than western monism. Would we be living different paradigms?
Sean, it’s nice to see you are carrying on the tradition.
Incompatible Arrows, I: Martin Amis
Incompatible Arrows, II: Kurt Vonnegut
Incompatible Arrows, III: Lewis Carroll
Incompatible Arrows, IV: F. Scott Fitzgerald
Also, there is a comparative view that one might think about in terms of the “valleys” and what genus figures are resting there, as we look at the “shape of space” and the relations you point out with regards to the Dark energy in relation to the universe? Mandelstam has pushed the boundaries of interpretation, and Jacques Distler in relation to Lee Smolin, can probably attest to that?:)
Please note the “Not even wrong index” as to the “in the box thinking” versus the “out of the box” thinking?:) This is not a reflection on any individual character, but an assessment of what comes as a result, to a coordinated frame of reference.:)
Boltzmann’s Reptilian Brain,
Can you say a little more about what was wrong in the 1975 article?
Am I the only one who finds that the debate over priors vs. dynamics is purely based on prejudice? Of course, to make progress in science we need prejudices about the unknown and hard solid work stemming from that prejudice, but to fight so vehemently about the metaphysics of it at this stage …
No, that seems to be sensible, ST.
Let’s say we take our physical system and measure its variables with great accuracy. Maybe our star, the sun. Can we recover all the information about its past states? Not even slightly. Can one recover the past history of solar sunspot distribution from a single high-resolution snapshot of the sun? Not any more than one could recover the history of all storms on the Earth’s oceans from a single snapshot from today.
Big Bang cosmology is a very special case our universe – we can indeed recover much information about the past state of our universe by looking at things like the cosmic microwave background radiation. This is very unusual, though – most information about the past states is irretrievable.
Take the example of the history of an nitrogen atom. We know that at some point, the nitrogen atom was formed via nuclear fusion within a star – or it could have been formed due to radioactive decay of 14-Carbon in our atmosphere. If we were to isolate a single N atom, we’d have no way of reconstructing its past history. Similarly, if we put 2 N atoms side by side and track them into the future, their paths would soon diverge.
Let’s say one of those N atoms gets swept up into a DNA molecule. It then forms the informational basis of a local entropy-defeating energy-dissipating dynamical system – the template. If we track DNA sequences forward through time, do we see “progress”? Well, what you do see is greater and greater informational complexity over time – with no particular aim at all other than protecting the informational template. Again, if we take a snapshot of all life on earth today, we can show that all life is inter-related, and that all life evolved from free-living single-celled creatures – but we lose most historical information.
In this regard, life is the ultimate pragmatist. Whichever way the arrow of time is running, that’s the direction that life works with. Thus, if you are ever trapped in a mysterious dynamical system, and can’t tell which way time is running, just look at any living creature, and you’ll be able to figure it out. 🙂
Of course this is a legitimate way to tell the story, given that the laws of physics are reversible. But, Universe doesn’t evolve this way. We see eternal expansion, not big Crunch. The real question would be, by my opinion – why the Universe doesn’t evolve this way?
Boltzmann’s Reptilian Brain: Hindsight is so very effective, especially fashionable with those who are expert at sneering. I’m not the one who sneered and I didn’t neglect anything worth considering. I just like to have seen Sean’s ideas presented with more detail that I haven’t already encountered numerous times elsewhere. I DO think Sean does good work and I do NOT fault him for the shortcomings of the article. I fault the editors and management of Sci Am, who generally present ALL physics articles as simplistically.
But it seems you’ve missed my point entirely. Whether the ideas expressed in the 1975 article have withstood the test of time is utterly irrelevant. (Sci Am itself links to it via Sean’s article). One wonders what your honest “opinion” on the matter was back in 1975 when that article appeared… or had you been born yet?
All I said was that Sci Am articles from 25+ years ago went into a level of detail which they come nowhere near approaching today. They really WERE better ARTICLES back then. I know this because I’ve subscribed to the magazine since 1964, and I’ve read every back issue extending back to 1900. The magazine peaked during the 50’s, 60’s and ’70’s. Since about the middle of the 80’s the content has slacked increasingly to the current pamphlet which delivers the published equivalent of sound bites. One wonders if the primary motivation for featuring occasional sexy (and “quickie”) articles on black holes and cosmology is to pump circulation up and draw readers to the advertisements.
John Merryman: “Maybe the material they have to work with is at fault.”
I suppose it’s conceivable, but I’m afraid I doubt that hypothesis. The decline in the magazine during the 80’s came in lock-step with a paper crisis and a general down-sizing free-for-all that became increasingly popular over the entire corporate sector back then. The magazine has never recovered from it.
Danny,
Gravity is the crunching of space and according to the most accurate measurements, those opposing factors are balanced, resulting in overall flat space, so the universe is doing both.
The problem is that the assumption is the expansion is due to an original singularity, and all other galaxies are actually receding from us and redshift is due to Doppler shift. Now that redshift has been measured to reflect a cosmological constant of space itself expanding, rather then drop the singularity and actually go back to Einstein’s original theory that space expands to balance gravity in one large cycle, thus the redshift of light that travels between them is simply redshifted because it is the light that takes the route least blocked by gravity fields and thus most expanded, cosmologists have come up with this patchwork mess where the contraction of gravity is divorced from any effect on the larger space, so in order to assert galaxies are actually moving apart and explain thermal equilibrium, etc., we have dark energy, inflation and all the other patches to shoehorn an measurably infinite space into a finite space theory.
Anchor,
They still have very rational articles on biology.
John Ramsden gives a beautiful and elegant description of our universe moving in two time directions. His description fits with some thinking I have done regarding this subject over the years.
If our universe is five dimensional this can be modelled as two four dimensional spheres each with three space dimensions and one time dimension. The time dimension would be opposite in one of these 4D spheres compared to the other.
The presence of dark energy has been postulated as the explanation for our expanding universe and as yet there is no theoretical basis for this explanation so it has been invented as an ad hoc solution to an observational dilemma. It is also known that the cosmological constant seems finely balanced to fit the observed flatness of our observable universe and the apparent balance between the forces expanding it and those that would result in its imminent collapse.
I believe that there could be an alternative explanation that could also explain inflation.
If the universe is seen as being like the inside of a black hole then the only way that such a black hole could expand is if a) the gravitational constant were increasing from near zero to the current strength, b) the speed of light were decreasing from an initial velocity close to infinity to our current speed and becoming even slower in future or c) if energy were to enter the universe/black hole from an external source.
If both a) and b) are true i.e. that ” G” is increasing and “c” is decreasing over time then eventually all matter will reside in black holes as even the gravity of an electron will have the capacity to hold in light that is travelling at a snails pace. The event horizon of all of these black holes would continue to expand until they all coalesce and once again all of the energy of the universe would be contained within a single event horizon that would usurp the original event horizon (diameter of the universe) this then would form the second half of the first 4D sphere of the 5D universe. Once this has occurred then “G” would start decreasing again to zero and “c” would start to increase to infinity again so that the event horizon/diameter would again shrink back to the Planck length type dimensions at the start of the Big Bang. At this point the process would start again. This could then be the second 4D sphere of the larger 5D universe. Its expansion and then contraction would end back at the beginning of the Big Bang of our 4D sphere.
I know that there has been no observation that indicates massive variations in G and c as indicated by alpha although this could occur if the Planck constant were also to grow larger in inverse proportion to the diminution of the speed of light. An increasing Planck constant would also help to explain how the tiny universe at the Big Bang could still have contained as many microstates as it does at its current size.
John, I do agree completely on what you have written, just one note – gravity is the geometry of spacetime, not just space. So what about the geometry of the Universe, is it open, closed or flat? The most recent measurements tell that the flat Universe is the most comprehensive explanation, given the dark energy and the observable amounts of dark and baryonic matter. Regarding recessional velocities of the galaxies, they recede from us faster and faster, and outside the Hubble sphere (which diameter is approx. 20 billions ly) they recede from us faster than light. Considering routes of light – don’t they simply follow the geodesics? Also, speed of light is constant only when strong gravitational fields are absent.
I love the article. I’m an avid reader of yours, so I was reasonably prepped — that probably helped.
You did lose me at one point. I don’t have it in front of me, but I felt I was following the microstate/macrostate statistical model of entropy until you wrote that quantum mechanics requires preservation of microstates (I’m messing this up) and thus the potential microstate complexity of the initial QM fluctuation that births a child universe could not be less than that of the universe itself.
Could you please consider a separate post on your blog in which you recap your very clear microstate/macrostate entropy discussion from the article, then reconcile that with the quantum mechanical constraint of total possible microstate preservation?
Thanks for writing the article. I’m a fan!
PS. For what it’s worth, I did my undergrad at caltech, albeit not in physics!
Sorry that I’ve been too busy to join in, but I did at least want to thank Ian (#33) for sharing the story of his daughter, and BRB for defending my honor.
John Faughnan, I’m not quite sure which part of the article you are referring to. Under any deterministic dynamics, specific microstates evolve into other specific microstates. At that level, to see an increase in entropy you have to coarse-grain; the entropy of a microstate is taken to be the entropy of the macrostate of which it is an element.
The bit about the early universe was trying to explain that you might be tricked into thinking that there weren’t many possible microstates back then, because the universe was small. But that’s incorrect, at least if we believe in deterministic evolution; all configurations are part of the same space of accessible conditions. There aren’t that many microstates that look like the early universe, but that’s just restating that the entropy was low, which is the problem we are trying to explain.
Danny,
Thank you for taking the time to think through what was a hasty post with many points crammed in it.
To further the heresy though, I do have problems with the commingling of time and space. I’ve been arguing on CV for some months (posts 24, 35, 40, 45, in this thread) that time is a consequence of motion, rather than basis for it. This would make it similar to temperature. The further question would be about the nature of space and whether it wouldn’t also qualify as a consequence of the motion defining it as well. My impression is that it is the void which constitutes the conceptual absolute. The alternative on which much of our theories are based is that the conceptual absolute is best defined as a dimensionless point. While it allows us the ability to set boundries, such as defining the entire universe as starting from such a point and space is thus created as it and the energy defining it expands from this source, as well as facilitating theoretical determinism, as all effects trace back to a singular cause, I think the void works much better as a conceptual basis. While the point constitutes a conceptual actuality, the void allows a much greater degree of potentialities. For one thing it wouldn’t be inherently deterministic, since there isn’t a singular starting point, but an infinite number. This also removes the entropy problem, since it cannot be defined as a closed set and energy lost in one place is traded around with energy losses and gains from other places.
As for cosmology, consider the consequences of a fluctuating vacuum(as opposed to an exploding singularity); The positive and negative forces are not stable and tend to collapse, but given that the environment is fluctuating and thus not stable, this collapsing isn’t even and rotations and other anomalies develop, so that the state of near equilibrium builds up ever larger vortexes that eventually explode, or otherwise eject and radiate away energies.(1) Thus forming the sea of gravitational wells set against expanding space. Since space is infinite to begin with, this expansion cannot increase the size of the entire universe as a singular unit, so it adds to the pressure applied to those gravity wells, causing them to spin faster than their internal attraction causes. So the need for dark matter is explained, not as additional internal attraction, but external pressure.
Since it is only the emptiest space which light travels the furtherest and this is what is expanding the most, galaxies are not actually moving apart on an absolute scale, so there is no need for the enormous amounts of additional energy required to actually drive them apart faster, which removes the need for dark energy.
An additional point I’ve made is that if space expands, our most basic measure of it, the speed of light, should increase proportionally. Otherwise it isn’t really expanding space, but increasing distance of stable space. Which poses other problems for Big Bang Theory, since the expansion of space as a medium was originally used to explain how other galaxies could all be redshifted directly away from us, without the earth being at the center of the universe. The rising loaf of raisin bread analogy. This effect of redshift proportional to distance is accounted for if expansion is simultaneously neutralized by gravitational contraction. An analogy for this might be that running up the down escalator doesn’t cause the floors to move apart, as the extra steps are pulled back into the system.
The further light travels, the more the effect is compounded, so that eventually a horizon line is created when the source appears to recede at the speed of light. While the source of direct visible light is no longer visible, black body radiation travels over this horizon line, explaining the bath of CMBR emanating from all directions at the approximate distance visible light ends.
So since I see the void as the basis for motion and time as a consequence of it, space and time are not the same. Yes, the math adds up, but the same logic used to describe how the measure of time is analogous with the measure of distance, since the device of lightspeed relates to both, could also be used to argue that the measure of temperature is analogous with the measure of volume, as a identical amount of energy occupying different volumes is going to have an inversely proportional temperature, but we understand the relationship is a triangulation of measurements relating to energy levels, not that temperature and volume are synonymous.
1. What if entire galaxies very occasionally exploded? For one thing it might explain the large voids occasionally found. If we have a universe that is infinitely old, it allows a far greater range of explanatory possibilities than trying to cram everything into 13.7 billion years.
Here’s a simple one: inelastic collisions. Totally classical physics, but inelastic collisions are not time-symmetric. Inelastic collisions are the basis for the formation of all structure in the Universe.
Isn’t this a simple enough argument to show that the arrow of time must run the way it does, and that despite the fact that most laws of physics for 2-body interactions are time-symmetric, the end macrostate doesn’t exhibit that time symmetry?