The Arrow of Time in Scientific American
Sean at 4:47 pm, May 21st, 2008
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.
Right. Because there clearly isn’t any difference in the macroscopic laws of physics with respect to time asymmetry.
Can you even imagine how one would go about envisioning the laws of physics spontaneously reversing a supernova, for instance?
Or, to take a simpler example, to un-fry an egg?
It might be a useful visual tool, to play with “what would happen if we ran time backwards,” but what do we learn from this? Anything physical seems unlikely.
Going to the lavatory is not going to be a pleasant experience! Shamelessly stolen from Red Dwarf: Backwards, which makes a comedy of this perspective.
Sean, that was a great read. Thanks.
Angular momentum is the strong arrow of time. Feynman’s sprinkler spins from emission but not in time-reversed absorption. The situation is not symmetric. A motion picture film can with an orthogonal port at its broad face’s center and another port tangent to its edge is an absolute direction of time detector. Fill with water then pump water center inflow to edge outflow. No problem. Reverse time - (nearly) no flow! Conservation of angular momentum creates a fluid diode with no internal obstructions.
Ah, but that’s what’s so fun about computational physics - “set Time Scale to -1″
What I really would like to see in any article on multiple universes is how to test the theory.
I tried to read this earlier, but as I have ADD, I find the written format to be a very poor one for data absorption. That is always a source of disappointment for me, because I love science. I thought to myself, “if only someone else could read this and summarize it for me in an illustrative way”. You have actually done just that in your timeline above. Thank you!
Sean,
You failed to mention Peter Lynds’ model - something which does address the initial conditions problem.
“What I really would like to see in any article on multiple universes is how to test the theory.”
Good point, and it’s long past time to refute people who think that it’s obvious that multiverse theories cannot be tested *in principle*. To be brief: this particular instance of the Popperian delusion is even more ludicrous than most. Just to get y’all started, read these:
http://arxiv.org/abs/hep-th/0612242
http://arxiv.org/abs/0704.3473
In reality, the problem with multiverse theories is to explain why we *don’t* see evidence of the other universes, why they don’t mess up our universe completely, etc etc etc. The whole “it isn’t science because other universes are not observable even in principle” industry is a load of rubbish.
Hi Sean
I enjoyed your Teaching Company Course on Dark Energy and Dark Matter.
I was reading this recent article from yahoo, “Missing Matter found in Deep Space” and would love to know your opinion
http://news.yahoo.com/s/nm/20080520/sc_nm/space_matter_dc
regards
Ronan
new baby universes as increasing of calculus? what is computing the multiverse? may be intelligent? why all that?
Boltmann’s Reptilian Brain,
Well, that is one very specific scenario, though, that of eternal inflation. There are other potential multiverse ideas that don’t predict any such effects. With Sean’s concept, the essential way of testing whether the theory makes any sense would be to show that a galaxy (or some other feature of our universe) is more likely to arise from a big bang like our own instead of fluctuating randomly out of the vacuum. Further testing is, of course, a really messy problem, but is in principle possible.
So, if for the sake of argument, no other universe other than our own exists, then what test would falsify the multiverse hypothesis?
Garth
So let me get this straight…. In the past week huge chunks of missing matter have been found and a supernova has been caught exploding. And you’re writing to tell us about an article you wrote?
I can understand the reverse or ‘mirror’ universe
like the reverse image/universe we see in a mirror.
But I can’t understand moving backwards in time
even in the morror one is walking backwards or forward >>> forward in time
@ Sean Carroll,
I want to translate this article into Bengali Language. So I need your permissio. I tried to get permission to translate an article of SciAm earlier and it was not easy. Finally I translated it without permissio but failed to publish anywhere.
I want to publish the Bengali translation in a Bengali Space Sciences Magazine name “Mohakash Barta” or “Space News”.
So, what do you say?
Another way to say it is that all particles move in only one (the one we call forward) direction in time, and this causes thermodynamics. The equations describing our microscopic laws are time-symmetric, but they apply in only the one direction. The laws of nature are not time-symmetric, because they include that constraint. Why is that? Why is alpha 1/137, and why is the Weinberg angle what it is? Because Mother Nature says so.
Khan– you would have to talk directly to the people at Scientific American. I don’t have the rights to the article. You should definitely not translate articles without permission!
“String theory”? How’s that?! Surely you can have quantum gravity, extra dimensions and other exotic phenomena naturally, but with string theory you have to have conciseness or con-science. I really don’t think you made a mistake when you wrote, “string theory” instead of strings.
I really enjoyed reading your article, that the first time I have enjoyed reading something about science since I read Brian Greene The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory.
except for the white holes, it sounds pretty familiar
not looking forward to the big crunch though…
It would be interesting to flesh out this timeline with some narrative describing biological and cultural evolution, and the lives of individuals, where history and memory play crucial roles, if only to emphasize how much time-reversed scenarios conflict with our understanding of our existence. The apparent indifference of the fundamental laws of physics to such considerations is perhaps the central problem.
Boltmann’s Reptilian Brain: “The whole “it isn’t science because other universes are not observable even in principle” industry is a load of rubbish.”
I’m not sure it’s an industry, but I agree with you.
Reptile and Joseph,
There is no industry claiming that “other universes are not observable even in principle”, since it is logically possible to come up with models with such observable effects.
On the other hand, there are a lot of people who want to see specific arguments about a multiverse make some sort of standard, testable (even if only in principle) scientific prediction before they agree that these specific arguments are science. I don’t see how the arguments being sold in Scientific American lead to any possible predictions that would allow one to test them in any conventional sense of scientific testability.
I’ve raised the point before, but; The only thing particles move through is space. Now with a sea of particles, they are creating a series of configurations, called events. Such as the earth and sun rotating and revolving relative to each other create days and years. While the physical reality goes from past to future events, these events go from being in the future to being in the past. So there are two directions of time implicit in this reality. Content going past to future, as form goes future to past. To the hands of the clock, it’s the face going counterclockwise. Our physical brain moves to the future, as our memory of past events fades into the past.
We understand there is no objective perspective, but we assume there is such a thing as an objective past, because it is unchanging. To the extent energy is conserved, information of the past is constantly being incorporated into the present, as the energy is recycled. So the past changes because it is being erased and any knowledge of it is due to information we are consuming and adding to. Time is like a rope being woven out of strands pulled from what was previously woven.
The result is that time has two directions, but no dimension because it is a consequence of motion, not the basis for it.
Xenophage on May 21st, 2008 at 8:01 pm
Angular momentum is the strong arrow of time. Feynman’s sprinkler spins from emission but not in time-reversed absorption. The situation is not symmetric. A motion picture film can with an orthogonal port at its broad face’s center and another port tangent to its edge is an absolute direction of time detector. Fill with water then pump water center inflow to edge outflow. No problem. Reverse time - (nearly) no flow! Conservation of angular momentum creates a fluid diode with no internal obstructions.
I believe the point is more subtle, because simply reversing the pump is not at all equivalent to reversing time. If you were to record the Feynman sprinkler setup and run the tape backwards, nothing unphysical would happen. Like light falling into stars the situation would look very strange but no law of nature is being violated.
The origin of the 2nd law of thermodynamics is no mystery. It’s been solved for decades at least.
Here are some references for those interested.
http://bayes.wustl.edu/etj/articles/gibbs.vs.boltzmann.pdf
http://bayes.wustl.edu/etj/articles/gibbs.paradox.pdf
http://www.ucl.ac.uk/~ucesjph/reality/entropy/text.html
Sean…
A very interesting and thoughtful article! It would be, I think, interesting to conjecture on how many frames of reference in the universe it would be necessary to conceive, assume, describe and understand before we could get an accurate mental pictorial concept of the true nature of cosmological reality.
Perhaps it would be appropriate to conceive of our “multiverse” as a progressive, eternal and infinite set of universes almost identical to our own, even including ourselves, but gradually and phylogenically developing along a single, single process time dimension, and increasing in informational complexity….
Garth Barber said: “So, if for the sake of argument, no other universe other than our own exists, then what test would falsify the multiverse hypothesis?”
That depends on how the work I mentioned progresses. It could easily happen, for example, that the theory will predict that new universes will nucleate at a rate and collide with ours with such effect that the theory can be ruled out by observations *already* made. Or, in the specific scenario considered by Sean, it may be possible to prove that new universes never look like ours. The point, as also made by Jason D, is that it is just not true that these theories are non-falsifiable *in principle*.
Peter Woit said: “On the other hand, there are a lot of people who want to see specific arguments about a multiverse make some sort of standard, testable (even if only in principle) scientific prediction before they agree that these specific arguments are science.
Look at the articles I cited. Seeing the patterns in the CMB described there would of course be very difficult — but you have no complaints about that, right?
“I don’t see how the arguments being sold in Scientific American lead to any possible predictions that would allow one to test them in any conventional sense of scientific testability.”
Exactly what people said — on better grounds — 25 years ago about Inflation. If I had been around 25 years ago, I would have been prepared to bet serious money that nothing observable would come out of such a theory within 25 years. And I would have been wrong.
There is nothing *in principle* unverifiable about Sean’s theory. One universe is born from another. Personally I would bet that a deeper investigation of this theory will show [sorry SC !] that it is actually not able to produce a universe like ours, except by some kind of Boltzmann-style massive fluctuation. Thinking about Boltzmann-style fluctuations has convinced most of us that it is not what happened. So at that point I would conclude that SC’s theory has been proved false. If that is not science then what is?
In short, nothing special is going on here philosophically. We have theories that posit *currently* unobservable things, just like any speculative theory. So what?
Anyway you might look again at Sean’s comprehensive demolition of John Horgan a couple of months back. He said it all better than I can.
I don’t see how anyone wouldn’t see how much more believable the standard cosmological model is than to hypothesize an “original intelligence” which created everything.
@ Ed,
Just because we are yet to understand something and at the present don`t have the technology to do that, it does`t mean that we shouldnt try….
Good point.
Can anyone help me imagining time going backwards?? If I reverse processes, I can only visualise it (the reversed process) as a going forward…..
“You should definitely not translate articles without permission!”
AHHH??!!!
Might as well be, “Quit thinking!”
You can’t read the article if english is your second language and you translate it first?
Just got the new issue of SciAm in the mail yesterday. Flipped to Sean’s article and started to read it out loud in the car while my 16 year old was driving to school this morning, thinking she might find it interesting (and having my eyes averted from the road keeps me from thinking about all the various possibilities of increasing entropy that she, as a beginning driver, narrowly avoids).
Unfortunately, I was unable to finish the article because, arriving at school, she asked to borrow it to share with her physics teacher today. The opening paragraphs completely grabbed her! This is the kind of stuff that gets her really excited and has her wanting to pursue physics/astronomy/cosmology in college in a couple years (She recently got the opportunity to spend the afternoon with your colleague Mike Brown at CalTech which she loved!).
So, thanks, Sean, for putting out this “high school-accessible” article. You definitely set the hook in at least one young reader! I look forward to finishing the article for myself tonight.
Khan, I think it’s great that you’ve offered to translate the article into Bengali. Send me an email offline and I’ll help you get the necessary permission. My email address is my first initial plus last name at sciam dot com.
manyoso, the problem isn’t the translation but the publishing! But actually I doubt there will be any problem at all.
George
Pete,
Here is a way to visualize time as going from the future into the past.
Rather then viewing time as a directional dimension along which we move from past to future, consider just a bunch of quantum energy that simply exists, with no time dimension at all. Suppose this energy developed the tendency to clump, then break apart and scatter, then clump again.
What this energy has done is to create a time dimension of events. Now since this dimension isn’t fundamental, but is created by the process of clumping and scattering, the quantum energy isn’t moving along it, but is creating it as each successive stage replaces the previous one. Since the only thing that exists is the energy, these stages go from being present to being past. The result is that this timeline is going from future potential, to present manifestation to past circumstance. This is one way to imagine time as going from future to past.
Sort of like tomorrow becomes yesterday.
Is it really that surprising that equations do not fully describe reality? A multiverse could be the difference in behavior/description at different scales within this universe.
Pete, I wholeheartedly, support and commend the activity of increasing our knowledge about our current and past environment (universe). That was not my point. I was pointing out that there isn’t much real difference in saying “in the beginning was void” and saying in the beginning was a tiny amount of vacuum energy.
Ed, thanks for explaining it, my mistake.
John,
So, what is going to happen has already happened and therefore isnt going to happen at all? Or am I approaching this in a wrong way?
This has twisted my brain.
Thought I just posted something, got a thank you, but, now I don’t see it.
Hoek
Pete,
I’m just making the point that the one dimensional, linear cause and effect narrative that we call time is better explained as a consequence of motion, similar to temperature, rather than the basis of it.
As a measure of motion, the concept of a specific dimensionless point in time is meaningless, as there would be no motion to measure, so nothing measured in time can be said to have an exact location. Reality really is fuzzy.
Sean
I liked your Scientific American article, but it seems to me that you
have neglected a significant component of the “time’s arrow” problem,
the part that some philosophers call the “now” problem.
Your article focused mainly on questions related to why the “beginning”
of the universe has more or less entropy than the other end, which is an
inherently interesting and non-trivial problem. But it misses the vital
question of what it is that “moves” under time’s arrow. The simple
answer is that what moves is an odd moment of time that we call “now.”
The problem of course is that there is nothing in physics that specifies
any particular instant of time as special in any way, and in particular,
nothing that specifies an instant called “now” that separates a
determined past from an indeterminate future. This might not be the
best definition of “now,” in that it opens up a set of difficult problems
about determinism that we don’t need just yet.
To sidestep these questions (for now), perhaps a better definition of
“now” is this: the moment of time that separates the time intervals that
all of us can remember from those intervals than none of us can
remember. At first we should probably assume that “now” is the same
moment for all of us, at least to some (poorly specified) accuracy. We
could define a separate “now” for each individual, but I don’t think we
need to do that just yet. We get into serious philosophical difficulties if
we assume that “now” for any one of us is separated by a “large” amount
of time from that for the rest of us, where “large” means something like
significantly greater than the light-travel-time between observers.
You touch on this question when you ask: “Why do we remember the
past but not the future?” You state that: “to form a reliable memory
requires that the past be orderly, that is, have a low entropy.” This
answer seems completely inadequate. Tomorrow may have a slightly
higher entropy than today, but not by an amount that explains the
radical difference in the behavior of memory over the two intervals. In
general, the difference in entropy in my surroundings between yesterday
and today isn’t very much different than the difference between
today and tomorrow. But there is a radical difference in what I can
remember about these days.
This raises another difficulty. Clearly there are large differences in the
change of entropy of our surroundings from day to day, as in the case,
say, of my house burning down compared to a more normal diurnal
interval. But I personally do not notice much difference in my memory
abilities, nothing that correlates with the magnitude of the change in
entropy from day to day.
It seems to me that a complete understanding of “time’s arrow” would
require an understanding of the “now” problem. It may even be the
more fundamental part of the problem, in that a theoretical
understanding of “now” might entail a full understanding of time’s arrow,
but an understanding of the entropy differences across the universe’s
lifetime would not appear to require an understanding of “now.”
Some philosophers, called “nowists,” attempt to resolve this difficulty by
assuming that “now” is the only instant of time that exists. This strikes
me as simply defining away the problem without explaining it. And it
has clear difficulties with special relativity. But I don’t have a
particularly better explanation.
Your very use of the words “past” and “future” assume the existence of
a “now” moment, but you do not deal with this problem at all.
Sean -
Heh, cool, I obviously like your timeline with respect to large
Within our conventional
scale reverse cosmology.
direction of time, I think you probably wrote your version first,
given how gaps between publication deadlines and “ink on
paper” usually work. I promise I have not hacked
into your ‘puter or travelled from your future after
having read your SciAm timeline!
A number of minutes ago I began typing a handwave about the weirdnesses of the two boundary conditions from the perspective of observers like us versus observers who see the evolution of the cosmos in reverse. This was derailed by two things, viz. conclusions that can be drawn about cosmic evolution in a Big Crunch direction, and whether reasoning about that end is really easier in either direction (forward physics or backwards physics) given a similar need for extrapolations in constucting timelines that include both boundary conditions.
It’s going to take a long hot shower to think about some of this.
One of the things that hit me was what the Hubble flow looks like to a reverse observer rather than a forwards observer who can simply play the “tape” backwards.
(Also there is another plausible case that is both helpful and distracting, namely, a pair of observers who are in a universe much like ours except that both boundary conditions are strongly predicted to be hot and dense. One observer looks “forwards” and one looks “backwards”. The differences between what either observer sees after his peculiar expansion-collapse transition and what the other observer sees after her peculiar expansion-collapse transsition is worth a thought.)
The second thing to hit me involved my immediate reaction was that the boundary condition of Big Collapse is easier to think about than either starting condition (Big Bang or “Horizon Decay”) because we only have to consider a couple oddities:
A. changes in the metric collapse of spacetime — e.g. it may be slowing down towards the big crunch, rather than proceeding at an even, “inertial” rate. (Here’s one place where backwardsverse!observer broke my brain, since I really get stuck thinking that their metric collapse of spacetime looks to them a lot like what we in forwardsverse think of as gravitational collapse).
B. it is not clear how the metric collapse can squish everything together to match the CMBR — we need a lot of energy to dissociate baryons (as we know from watching stellar reductions), but the energy from the metric collapse force seems insufficient, especially with respect to singularity models of the Big Collapse.
In point (B) I wanted to predict “cosmic deflation” but my brain bent less because of mechanism (just play it backwards) than because of what could suggest it to any of our Big Crunch predictors.
I also am tired and easily distracted by trying to add in things like possible quintessence, predictions from QM (dehadronization) and the like. You can have a lot of fun running various models backwards and forwards! Maybe everyone should do this out of habit if “Given that the laws of physics are reversible” is true.
Penultimately, I wanted to avoid dragging everyone into long debates about the nature of reason (I’m in the “it’s an emergent property of brain structure/function/mechanics” camp), since that doesn’t obviously help with the thinking about boundary conditions, but is one of those interesting distractions.
This started getting very hard when thinking about how our backwards counterparts would perceive CMBR, for example.
Finally, notch up another commenter who likes before-bedtime activities, even if he is a total outlier in your timezone-to-posting-hour distribution (UTC+1).
Your friendly neighbourhood rodent toxin of many names.
3 Meta points:
1. Add me to the list of people who wish for a preview button!
2. I obviously did not foresee the mangling of the link to my previous comment, but I figure you are smart and can figure it out.
3. As one way to sidestep the problems of observation and communication involving people with incompatible arrows of time, how about pretending there exists a translation system that lets you write down the observations and reasonings of a “foreign” (in the evolution of the universe sense) cosmologist acting just as his/her/it’s agent? I wish I could find a more concise and academic description than here:
http://tvtropes.org/pmwiki/pmwiki.php/Main/LiteraryAgentHypothesis
in which it is argued that some proper scientists have employed the device at least when writing hard science fiction.
I was using it earlier without really thinking about it or acknowledging it.
Perhaps someone will have a “conversation” with a scientist in backwards-universe and report back details? Or at least bury the use of such a reasoning device behind something more conventional and rigorous, along the lines of what you might find on arXiv or at least main postings on cosmicvariance.com?
Finally: Warning: tvtropes.org will ruin your life, or annoy you, or both. It says so itself on the front page. Apologies in advance.
Here’s a Sci Am article on the arrow of time that is interesting on quite a number of levels:
http://www.sciam.com/media/pdf/2008-05-21_1975-carroll-story.pdf
One of the reasons why it’s interesting is because it’s 1/3 century old. Another is that it doesn’t treat it’s readers as if they are terminally afflicted with ADD.
No offence, Sean, but I wistfully long for the days when Sci Am published elegant articles that served up some actual meat in them, “articles” that didn’t resemble a television commercial with eye-catching and monumentally irrelevant cgi artwork. Then one looks “under the hood” and finds watered-down soup that looks as if it was hammered out over a weekend rather than the hoped-for beefy stew. I spent as much time - maybe ten minutes total - admiring the opening art as it took me to read the article, which provides almost no further elaboration of the concepts that isn’t already encapsulated by the 3 so-called “infographic” boxes. Unfortunately, the article fails miserably in terms of actually learning anything new.
Just how far can they possibly push this “simplification” gambit before anyone notices that the “articles” are basically appetizers for what readers REALLY want in a magazine subscription - you know, like a satisfying meal?
Though they can still work up a fair sweat with biological topics, in terms of physics and astronomy articles, Sci Am has become a dreadful waste of the precious resource of paper. Looking over how the magazine has diluted the information content in it’s articles over the last 20 years or so, it’s apparent that they’ve finally settled on identifying their market: moderately bright grade-schoolers who have the attention-span of a gnat.
Doug,
The entropy problem would go away if cosmology wasn’t trying to define the universe as a sungular unit with an internal timeline that goes from beginning to end, as its external position goes from being in the future to being in the past. If it’s infinite there is universal energy exchange and all energy is conserved.
“Now” makes much more sense if we consider that only energy in space exists and time is a consequence of measuring change. Therefore, as I previously mentioned, “now” cannot be a dimensionless point, as there would be no motion to measure.
W. Arfarin,
If you think of energy expansion as the source of redshift, it is the hands of the clock of constituent energy going from one temporal unit to the next, as as gravitational structure is the face of the clock, with its units of measure going from being in the future to being in the past. That way, you have a convective cycle of expanding energy and collapsing mass, rather than a universe as a singular unit of time.
Anchor,
Maybe the material they have to work with is at fault.
The apparent symmetry of time in physics could well be due to the inability of equations to fully capture and describe time. The convention is just that, a convention.
I hope I am not being annoying…
John Merryman -
No, my thinking rathole about the Hubble flow, specifically from
the point of view of an observer who sees *this* universe (more precisely, our Hubble volume) in the
opposite time-like direction from us, went like this:
1. Can a biology arise in reversed standard cosmology?
(a) We can guess what it looks like — the (generic) luciferase
process looks a lot like the chloroplast membrane proton gradient-ATP Synthase process in reverse!universe: photons are
absorbed and used to phosphorylate AMP; the resulting ATP
can do work (e.g. breaking apart polymers in ribosomes,
synthesizing carbohydrates in mitochondria,
bioluminescing in chloroplasts…)
(b) Origin of life problem seems pretty damn hard, but it’s
not exactly easy in forwards universe
(c) Adaptation and natural selection is a bit
confounding in reverse, especially if we look at it
forwardsly — it seems like a spectacularly
unsuccessful species whose population dwindles rapidly
towards zero would be well adapted to a niche in reverse
2. Can a biology in reverse standard cosmology result in a
brain that reasons like our brains?
I have nothing other than resorting to the law of large
numbers, which as we know produces Boltzmann Brain
problems in forwardsverse; my poor brain needs some
pencils and paper to think about it backwards. My “yes”
is purely intuitive.
3. “Seeing”
An obvious development in sensory equipment comes down to
“sourcing” photons from biomechanical processes that emit
them with a nonthermal distribution that can be tracked
from point of emission. (No feedback in backwardsverse is
an assumption to help preserve Galilean invariance and
Lorentz covariance).
In backwardsverse we would want to evolve strucuress which emit
photons in such a way that the resulting work preserves
(”encodes”) very fine grained angular distribution
information about the photons (as well as their energies).
“Seeing” reversed: photons stream out of phototransmissors
in all sorts of directions with anisotropies at different
frequencies. At point of emission we can preserve
information about the direction of distant photon sinks.
Using this to examine the sky we would see large areas
which “suck” only low numbers of low frequency low
temperature photons from our photoemissors. We would see
quite a few pointlike and smearlike objects which would
“suck” out larger numbers of much higher energy photons,
and so forth. A hot blackbody sinker has a well defined
photon sucking behaviour in terms of photon frequencies;
many other hot objects (especially in the sky and in labs)
do not take a full blackbody spectrum. Doppler effects
shift these spectral lines towards higher frequencies or
lower frequencies depending on the relative motions of the
observer and distant photon attractor.
Rotating and elliptical galaxies and huge stellar implosions are pretty
uniformly distributed across the sky. When we send out
photons to them we notice a correlation between decreasing
angle and increasing blueshift, corresponding to a metric
collapse of space time of approximately 71 km/s/Mpc.
When we send out very blueshifted galactic spectra to a
narrow angle of sky we are really transmitting photons
into the distant past, where they will ultimately meet up
with their appropriate photon sinks, in line with what we
know about the second law of thermodynamics.
Unfortunately we cannot say much about the present state
of the sinks of these distant photons, except that they
are probably further away from us now (and probably more
filled with metal) than is suggested by the outgoing spectra.
4. This is far from rigorous and hinges on forward
reasoning informed by backwards perception (i.e., something that thinks like us but which we would probably guess was thinking backwards — “remembering the future” when it is really remembering its own past).
This is not forbidden by an emergentist view of reasoning, but I have no idea how likely or unlikely it could be. Is it more or less likely than our own reasoning?
This point also lends itself to metaphysical thinking which,
frankly, annoys me.
Lastly, with respect to your paragraph staring with “if
you think of energy expansion as the source of
redshift”…
I don’t want to do that; that’s not an approach that
is interesting to me. I am not trying to disprove the
concordance model AT ALL, I am trying to better understand
it by inverting the timelike direction of observation with
a few assumptions (reversibility of physical processes, fundamentally).
As a result, I am (trying to be) thinking of the Hubble
flow in standard cosmology terms (without being
particularly rigorous), just in a timelike direction that
leads to the Big Crunch (i.e. what we call the Big Bang).
That is, the “clock” direction in this is with respect to
the boundary conditions, particularly the one which is
strongly predicted (our hot dense early universe). The
clock metric favoured in Sean’s threads is entropy
(specifically the log relation of microstates to
macrostates), which increases in one direction and
decreases in the other.
Trying to predict the observations of a human-like
reasoner who happens to be used to the reverse direction
(i.e., entropy decreases over time) is hard, particularly
since I am scratching my head about things like
thermodynamic favourability versus forward logic, and
whether when we flip the thermodynamic arrow we also flip
*whether* things like electron transport chains, osmosis,
exclusive or logic gates, and so forth *can* work, rather
than *how* they could work.
Particularly with respect to this rathole, I’m
not especially keen on considering possible states outside
the Hubble volume or beyond the BB/BR (and even the Big
Rip (or Long Asymptotic Isolation) end is a bit fuzzy)
without good reason.
So, to reiterate, thinking about time reversal like this is at best an exercise that might be useful to explore the standard cosmology, and at worst is Anchor’s “dreadful waste of [some] precious resource”. Science-shattering? No. Interesting? I think so, otherwise I’d be doing something else with this. Useful? I dunno. Ask Sean Carroll.
- Your friendly neighbourhood etc.
I wonder if the answer to this might not be hiding in plain sight. E=MC(Squared). A useful formulation that even Einstein had to tinker with, even if just a little. Our physics have no explanation for what happens past the “speed” of light. On the other hand our physics, certainly on our own little macro level, depends upon a formula that includes 3 elements, one of which clearly does not exist — the speed of light squared. What might energy, matter, time, or space be, or would they be, in a multiverse where one “sector” was ordered on laws of physics where the speed of light squared was the rule rather than the exception?
Brody,
My problem is the path down this particular hole started with a question about the expanding universe. Many years ago I happened to read that the sum of total expansion is very close to, if not evenly balanced by the contraction of gravity. So I’ve raised the issue of how can the entire universe be expanding, if this spatial expansion on which the assumption is based is being effectively neutralized by gravity. Now I can certainly understand why you wouldn’t want to question BBT, as it classifies one as a crackpot to do so.
On the other hand, I’m not a scientist and in fact my main interests tend toward politics and history and I only started reading up on physics as a way to gain insight as to what motivates the larger forces in society. So when I come across bunches of people all marching in the same direction because the best and brightest told them it’s the way to go, even though the logic is incomplete, incoherent and full of patches, my impression is decidedly less then credulous. When the adherents try an enlighten me by by pointing out that it’s ordained by a higher power, in this case, mathematics and I’m just too simple to understand, I don’t necessarily assume I’m just too thick to appreciate that we are living in a new era, but tend to consider the crowd might just be falling for another version of the same old song and dance. As far as I’m concerned, equations are another form of smoke and mirrors when those promoting them cannot explain what they mean in another language. In this case, english.
As for cosmology and time, if gravitational collapse is an inward curvature of space, than I am of the opinion the radiation and other forms of energy being ejected from gravitational wells amounts to an outward curvature of space and redshift is evidence of this cosmological constant. The result being an old fashioned convective cycle of collapsing mass that heats up and starts expanding, until it cools sufficiently to start the cycle over. As structure, mass is the face of the clock, with its units starting as future potential and ending up as past circumstance, while the outward flow of radiation/energy is the hands of the clock, the raw essence that is constantly shedding/radiating away from old forms and starting new ones. It is both of these directions of time coexisting, the outward expansion into the future and the inward collapse of the past, that forms this infinitely dimensional reality we live in.
As for math, it is a model, not an ideal.
Anchor sneered: “No offence, Sean, but I wistfully long for the days when Sci Am published elegant articles that served up some actual meat in them, “articles” that didn’t resemble a television commercial with eye-catching and monumentally irrelevant cgi artwork.”
Yeah, well, Anchor, “no offence”, but you are neglecting one tiny point: that article from 1975 is wrong, though at least it correctly identifies cosmology as the source of the Arrow — incredibly, there are still some people who dispute this obvious fact. Nevertheless the solution proposed is indeed wrong. Here’s a free clue: the theory advanced there sank without a trace.
Sean’s article may seem simplistic, but that’s the point: what he is trying to draw to your attention is something which is indeed amazingly obvious, yet people —- I mean professional physicists, not just crackpots like Last Mohican —- just don’t get it. Quite recently I had a discussion with a distinguished physicist. I asked him what he thought about the old idea that the arrow might reverse if the universe began to contract. His response: “that’s ridiculous, it would require incredible correlations, etc etc etc” But he didn’t think that there was anything ridiculous about the fantastic correlations that you see if you trace the history of our universe back to the big bang! So you see that even the simplest errors in this subject live on, and Sean is doing great work in alerting everyone — not just the public — to those errors.
ps. No, I don’t believe that the arrow will reverse if the universe contracts. The point is that the history we observe is just as bizarre as that would be, and cries out for an explanation. Meta-point: there is obviously some major gap in our understanding of the early universe. If we can’t understand this, then we are probably getting lots of other things wrong too.
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?
Inelastic collisions are just completely conventional examples of macroscopic time-asymmetry: start with low-entropy initial conditions, and watch the entropy increase. (Inelastic collisions produce heat, sound, and stresses, all of which increase the entropy.) They have nothing to do with why the arrow of time “must” run the way it does, since they say nothing about why the entropy was low to begin with.
What about wavefunction collapse or world-splitting (or whatever)? A particle seems more ordered than a wave (but maybe not), and i guess the larger system must be taken into account. In an Everett scenario, is the tree balanced on both sides?
What was Veneziano thinking?;)
And it’s Gabriele Veneziano. He is what we call a “super cosmologist” because, he thinks “outside the box.”:)
No, sorry. I didn’t meant that this explains why the entropy of the Universe was low to begin with. But as far as I understand it, it doesn’t matter what the value of entropy is or was at any point.
What matters is that the entropy is higher now than it was in the past. All the interactions that we know of either increase entropy or conserve it. I guess what I don’t understand is what all the fuss is over. You have some initial state, like a nearly homogeneous and isotropic expanding Universe, it evolves according to the laws of physics, entropy increases, the end.
Given that our Universe obeys the laws of physics we know, I don’t understand what question you’re actually attempting to address about the arrow of time.
“You have some initial state, like a nearly homogeneous and isotropic expanding Universe,”
Why?
That’s the question.
Energy radiates across 13.7 billion lightyears. Gravitational structure coalesces from within a radius of a few hundred million lightyears. While the energy loss of radiation is diffused across much more area then the gases from which mass congeals, it is also radiating in from the same amount of area. Unless of course you assume it’s all just expanding into a void that doesn’t otherwise exist, from a point that has no boundaries. All the while measured in lightspeed that remains stable, as the very space it measures expands. It is a question.
Neil,