# Why no time before the BB?

1. Jul 16, 2015

### Robert P

Why is it said that time didn't exist before the BB and the creation of the universe? As I understand it, the BB is theorized to have come from a ball of something. This something had to have some kind of properties, events that occurred within whatever state it was in, and these events would have occupied time.

2. Jul 16, 2015

### Staff: Mentor

Here's a quote from the wikipedia article on the BB that sums it up nicely:

from the article:

https://en.wikipedia.org/wiki/Big_Bang

Last edited: Jul 16, 2015
3. Jul 16, 2015

### Chalnoth

The classical big bang is necessarily incorrect at the start. We have lots of different models that replace the mechanics that occurred very early-on to avoid the Big Bang Theory's problems at the earliest times. We still usually use the Big Bang Theory to point to a specific time and call that the start (sometimes that specific time is called the Big Bang). What happened before that specific time depends upon what model we use to replace the Big Bang Theory. There are some models where there is a beginning, but no time exists before that point. In other models, time extends infinitely far into the past, with the Big Bang just being one event along the way.

4. Jul 16, 2015

### Chronos

Devoid of energy, no physical processes transpired prior to the emergence of the universe [i.e., the classical BB], hence no measures of time [clocks] existed. We may therefore conclude time did not exist prior to the classical BB in any physically definable sense.

Last edited: Jul 16, 2015
5. Jul 16, 2015

### Robert P

You're saying you think there was no energy prior to the BB?

6. Jul 16, 2015

### phinds

The currently accepted theory of cosmology is that we don't know WHAT, if anything, existed prior to one Plank Time after the "t=0" time to which the math model extrapolates backwards. "Singularity" just means "the place where the math model breaks down and we don't know what was/is going on". The Big Bang Theory is a description of what happened from one Plank Time forward.

7. Jul 16, 2015

### Chronos

Allow me to add that phinds is entirely correct, the BB is a model that describes how the universe evolved after its origin. It does not attempt to explain the origin of the universe, or if it even has an origin. We are, however, fairly certain the universe is not infinitely old in the form in which it currently exists. We do not, for example, observe burnt out cinders of stars that 'died' of old age [aka black dwarfs] after exhausting their fuel supply. We also observe an inexplicable abundance of radioactive elements produced by massive stars that would otherwise have decayed to trace levels, or even beyond detectable limits, in a universe of infinite age. So the question remains open on the origin of the universe. Two major choices are available: One idea, that has gained new life over the past couple decades, is an eternal universe that periodically destroys itself and re emerges like a Phoenix from its own ashes. This is popular known as the cyclical, or bouncing model of the universe. The other model is origin via a quantum fluctuation whereby all the matter, energy, space and even time itself emerged from a primordial quantum fluctuation in the nothingness that preceeeded the BB. That is the model I was implying in my comment regarding no energy [or time] prior to the BB. This is also popularly known to as the universe from nothing model. It remains popular despite the obvious question - 'how does nothing fluctuate?' The answer to that query lies deeply buried in the recesses of quantum physics. It offends the sensibilities of practical souls who struggle with the concept of something from nothing. Irrespective of which class of models one may prefer, the question ultimately becomes, depending on your philosophical leanings - has the universe always existed in some respect or another and evolves eternally, or did it emerge from some fundamental creation event at some point in the remote past? If time is not an absolute and fundamental property of reality, it was meaningless before there was a universe.

8. Jul 18, 2015

### slatts

This seems true, but only if form includes scale. Before atomic structure became widely understood about 1900, I don't believe it did: A scaled-down model was considered to have the same "form" as the original it depicted, with "form" having been the equivalent of what we might be likelier to call "shape" nowadays. What the originator of this thread may want to bear in mind is that there ARE detectable limits: There is a size of object whose outlines could not be revealed visibly to us (OR "by us"), even if all the mass / energy of our universe could somehow be devoted exclusively to its magnification. Our entire universe would, likewise, remain totally and permanently undetectable to a surrounding universe larger than it by a factor sufficiently huge, although, within a certain fringe of detectability, I believe that phenomena would appear random, since, although their elements might generally be perceived, they might never be perceptible clearly enough to reveal their relations to each other.

I'd be interested to know, from people more familiar than myself with quantum theory (-which would probably include at least half the participants in this forum) whether the "quantum tunneling from nothing" posited by Vilenkin (which does have some power of explaining why the so-called "initial" gob of matter and/or energy didn't collapse into a black hole) may simply appear possible as the result of this limitation.

Last edited: Jul 18, 2015
9. Jul 19, 2015

### Chronos

That, i would say, is an interesting question, in which case one could argue we would not be here to pose that query. To that extent I would appeal to the weak anthropic principle.That solves the philosophic issues, the rest is left to science, imo.

10. Jul 19, 2015

### slatts

Sorry; I worded my inquiry a little carelessly. I didn't mean to imply that acceptance of the possibility that quantum tunneling from nothing may have occurred requires any leap of faith. I was just commenting that, as far as I've been able to tell, "nothing" means "probably closer to absolutely nothing than it is to the smallest currently observable unit of the quantity concerned", and kind of hoping that there might be some factor in the math involved that would take account of whatever that quantity might've been at the time of a conjecture. (Vilenkin himself has repeatedly compared his "quantum tunneling from nothing" with Hawking & Hartle's "wave function of the universe", which, as he doesn't hesitate to imply,would've allowed purely hypothetical beings to observe a distinction between space and time under conditions of lower energy density than are now generally considered to have prevailed in the inflationary epoch.)

My guess is that there probably isn't any such factor, which has the interesting effect of leaving the historical context of fundamental theorizing essential in validating it. (This isn't the case for vastly less fundamental scientific observations: For instance, a weatherman seeing only a single flake of snow drift by, during the period between one observation and the next, is obligated to write "trace of snowfall" in the record, whereas, if he didn't see it, he'd write "snowfall zero", and anyone familiar with the record keeping would realize that a flake might nevertheless have landed at his post. To coin a phrase.)

11. Jul 19, 2015

### Finny

For Robert P who started this thread: The above question MIGHT seem to throw considerable doubt on a 'new beginning' or 'beginning from nothing'. But it's not necessarily as big an obstacle as you might think.

On one hand it is believed via quantum mechanics the 'nothingness' of open, free space is in fact filled with vacuum energy which on balance is zero. From a general relativity [GR] perspective, if the universe we live in exactly balances negative gravitational energy with the positive mass energy, and it seems at least close to doing so, all we have now is a different state of 'nothing'...zero in total. Alas, GR does not yet have a single, firm uncontested view of the total energy in the universe.

12. Jul 19, 2015

### slatts

THAT's the problem with ANY "beginning" to everything....no matter (-no pun intended) how many particles of matter and energy there are, any interactions between them would, even if random only in appearance, sooner or later put them into gridlock, with a "stuck on dead center" effect that's familiar to students of steam and internal-combustion engines. That this hasn't happened yet requires a "specialness" familiar to psychiatrists studying "ideas of reference" in people suffering from schizophrenia.

13. Jul 19, 2015

### Finny

What is 'gridlock'?? Not stasis I hope.

If I understand your post, that's not actually the case. Nature generally moves towards a state of maximum entropy which in the absence of gravity means, for example, a gas or photons released into a room distribute themselves rather evenly around the available space. That maximizes entropy and minimizes information. And the universe works in the same general direction. In the presence of strong gravity, clumping is the state of maximum entropy, hence stars,planets, black holes and galaxies, but few would describe any of that as 'gridlock'.
Not even the vacuum state is in gridlock.

14. Jul 19, 2015

### slatts

No, sorry, I don't think I made my last post clear enough. I'm not saying that the universe is in gridlock; I'm saying that the fact that it's NOT in gridlock leaves it improbable that it had any absolute beginning. Relative "beginnings" (or relative "endings") seem plausible to me, as long as each such occurrence is on a scale different from the scale of the object concerned upon its previous ending. My post #10 in this thread was intended to show that I feel the terminology to be relative (i.e., dependent on its context), rather than absolute.

I'm aware of the entropy problem, which is usually felt to apply even even to cyclical (or "bouncing") cosmologies, if there is a minimum size below which the temporally-reversed version of the hypothesized universes concerned cannot be extended. (I've heard that Steinhardt & Turok's "ekpyrotic" proposal of periodically colliding branes--membranes of the vibrating strings very often hypothesized as defining what had previously been seen as "elementary particles"--employs a special field to neutralize the fatal increase of entropy's density, but that seems a little too ad hoc for me.)

What I can't understand is why there would BE any minimum scale, either of space or of time. I understand that, if there was, reliable calculations involving infinities would be easier to make, but for physicists to consequently wish that there was one is like bus drivers wishing for power steering--the wish was natural, but its connection to a larger reality is lacking, as far as I've been able to tell (-and, in the attempt to understand this mania, I've read entire books by Smolin and Bojowald).

I'm NOT saying that reality is not divided into quanta: It probably IS, at least in all inhabited and habitable regions, and even in all regions accessible in principle. I AM saying that I haven't yet heard why the number of spatial scales, or the number of temporal scales, would have any limitation whatsoever, except "LOCALLY". In this connection, I guess I should add an assumption of mine that any difference in the set of spatial and temporal scales applicable in different regions would cause them to repel each other with extreme force and rapidity, although the only scientific basis for this assumption is the existence of some of Andrei Linde's older work, which hypothesized a universe inside a monopole. (The papers are pre-Web, and my math skills wouldn't justify harassing a librarian enough to get a hold of them.)

Sorry for all the bold-facing; I'm just trying to get around the dullness of my convoluted writing (attempted verbal imitation of math, but not quite as concise, huh? Probably not as accurate, either, but that's why I'm posting it).

Last edited: Jul 19, 2015
15. Jul 21, 2015

### Finny

"What I can't understand is why there would BE any minimum scale, either of space or of time.

Quantum principles don't always match our classical logic. I was just watching a SUSSKIND video and apparently he likes to start most of his quantum lectures with such an explanation: Evolution did not require us to evolve quantum logic.

Anyway, It seems we live in a quantum world. But that necessarily breaks down, or so it seems, at the Planck scale due to the uncertainty principle.

I'd been looking for this description after not not having seen it for a long time:
"Any photon energetic enough to precisely measure a Planck-sized object could actually create a particle of that dimension, but it would be massive enough to immediately become a black hole (a.k.a. Planck particle), thus completely distorting that region of space, and swallowing the photon. This is the most extreme example possible of the uncertainty principle, and explains why only a quantum gravity theory reconciling general relativity with quantum mechanics will allow us to understand the dynamics of space-time at this scale.

https://en.wikipedia.org/wiki/Planck_scale

More generally, the known laws of physics are not much help because they describe how things evolve in time not how time begins. They do not describe the big bang itself.

16. Jul 22, 2015

### slatts

Wow, that's terrific! I feel a little like I imagine Brian Greene may've felt, when he realized that galactic structures were the CMB 'writ large'! Given the obsession with an absolute beginning in physics (or at least in its popularizations, to which my mathematical ignorance often confines me), I'd always figured that the changes in scale I'd thought it might represent would've been dramatic, but even the possibility that some little upward kick in energy density even might have suddenly transformed an entire generation of steroidal photons (into very little more than hole-black space) was jaw-dropping! Especially since some googling inspired by your post about the possibility of a zero energy balance had, not an hour before, turned up

https://www.sciencenews.org/article/arrow-time

, which describes simulations of gravitational clumping being conducted (by a group led by Julian Barbour, no less). A distinct maximum in the clumping is apparently occurring with equal chances at either early or late times in each simulation, which is suggestive of dual arrows of time pointing in opposite directions. To a layman like myself, this seemed very similar to the dual-arrowed universe modeled by Aguirre & Gratton (and described somewhat favorably by Vilenkin at

arXiv.org > hep-th > arXiv:1305.3836 ), except that the arrows in the AG scenario were thermodynamic rather than gravitational.

The Barbour study may invalidate a lot of things about the relation between entropy and time, so that the statement answering the question, " No time before the big bang?", could turn out to be, "Time behind the BB."

17. Jul 22, 2015

### Chronos

I think that position relies on numerous unsupported assumptions. I am willing to concede entropy may be poorly defined by current science, but, so is gravity. I suspect a good theory of quantum gravity might resolve both issues. I am fond of the thermodynamic approach to both gravity and entropy, it appeals to my sense they must be fundamentally related.

18. Jul 22, 2015

### slatts

Having been a big fan of the dual arrows of time as formulated by Aguirre (who, when cornered by the Science News reporter, didn't seem to cotton to Barbour's approach), I am curious about a thermodynamic approach to gravity. Can you maybe provide a reference to an article or book, hopefully one that might paraphrase the main points of its QM and math with plain English?

Last edited: Jul 22, 2015
19. Jul 22, 2015

### Chronos

20. Jul 28, 2015

### ohwilleke

One possibility is that an antimatter dominated universe expands backward in time from the Big Bang in the same manner that our matter dominated universe expands forward in time from the Big Bang.

In that scenario, the sole arrow of time in the universe would be entropy which flows from a peak at the Big Bang in opposite directions in time. Time basically would flow backward in the antimatter universe which fits with the conceptualization of antimatter, which flows naturally from the concept that a Feynman diagram can hold true for any rotation in space-time coordinates, that antimatter is basically ordinary matter moving backward in time. In this cosmology, causality is an emergent property of the universe, rather than a fundamental one. Forward in time operationally would mean "away from the Big Bang" and would only be well defined in systems complex enough for entropy to be well defined.

Thus, it would be perfectly sensible in the case of entangled particles for information about how one entangled particle resolved when measured from an indeterminate state to travel back in time to the point of entanglement and then forward in time against on the path of the other entangled particle until it resolved from an indeterminate state in a correlated way without leaving the light cone, acting non-locally, or determining in advance at the time of entanglement how it would resolve from an indeterminate state.

All of the laws of the Standard Model would apply identically at both t<0 and t>0 with the antimatter universe having particles that are CP flipped from our own. The Standard Model distinguishes through CP violation between forward in time and backward in time, but does not on its face obviously prefer one to the other. The two universes could evolve from the Big Bang differently (i.e. there wouldn't necessary be a parallel planet Earth in t<0, just a universe that evolves according to the laws of physics from the other side of the Big Bang according to the same rules making it extremely similar in a fine grained way, but not identical since there would be nothing to link events in the t<0 universe to events in the t>0 universe).

The amount of matter-energy in any time-like slice of this universe would be the same, pursuant to the conservation of matter-energy.

The aggregate baryon number and lepton number of our universe would be reversed in the part of the universe prior to t=0. The total baryon number in the universe over all time from negative infinity to positive infinity would be zero, as would the total lepton number of the universe. Nothing in this conception explains why the aggregate baryon number and aggregate lepton number of the universe ends up the way that it does; this would have to flow from unknown physics at Big Bang energy scales governing how pure energy condenses into particles, but could involve some scenario in which baryon number and lepton number arise from baryon number conserving pair production and from lepton number pair production that straddles t=0 (with all pairs produced exclusively on either side of t=0 quickly annihilating into energy in almost every case).

Since this universe provides a natural explanation for matter-antimatter asymmetry and a finite B and L number for the universe without needing non-sphaleron B and L violating processes to give rise to the universe from a starting point of pure energy, B and L can be perfectly conserved and phenomena that merely conserve B-L such as Majorana fermions and supersymmetric violations of B or L separately are not needed and there is no neutrinoless double beta decay.

If one wants to get really clever with the concept it can also be used to explain the "Bang" element of the Big Bang, with the energy that drives it all flowing from antimatter on our side of the Big Bang rushing back towards t=0, while ordinary matter on the other side of t=0 rushes forward in time, and matter-antimatter annihilation occurring in the region that is ill sorted between matter and antimatter (to a degree consistent with the uncertainty principle) as matter and antimatter try to sort themselves into the right universe an collide en route. All pair production that does not straddle t=0 contributes to the "Bang".

Such a universe is finite with spatial dimensions identical to our own but with twice the extent in the time dimension. Philosophically, it assumes fate with free will and randomness merely being illusions (or perhaps more accurately, concepts that are only well defined from the perspective of an observer in a particular time slice that cease to have meaning in the case of a hypothetical but nonexistant "eye of God" observer). From the perspective of an "eye of God" observer, there is precisely one four dimensional universe that is like a painting always existing that only seems random from the perspective of an observer at a particular point within it who does not have knowledge of the whole. Time travel paradoxes would be prevented because there is only one consistent story of space-time - rather than many worlds or "the multiverse", there would be only one possible outcome of every event even though it would seem at the time to be perfectly random, "the monoverse"

If the monoverse does not have a critical density necessary for the expansion of the universe to stop and start contracting instead (indeed, I'm not sure with entropy defined as it is in this universe if the laws of physics could ever permit a contraction), then the monoverse is ultimately infinite in time and space extent in every direction, even though there is a huge infinite region beyond the expanding universe's own "event horizon" in space-time at its frontier that is permanently inaccessible and effectively does not exist (which is fine because as mathematicians know, there can be different orders of infinity that are not necessarily equal in size to each other). The theory is agnostic on the question of what exists beyond its event horizon, but that event horizon boundary at its space-time frontier is far less arbitrary that the conventional Big Bang analysis with time and space starting from nothing. Instead, the Big Bang is conceptualized as basically the center of a four dimensional sphere that extends from that center in all directions to infinity, with the nothing beyond the spatial horizon only having nothing in it until enough time passes to cross that point. The speed of light boundary makes it theoretically impossible to leave the monoverse.

This is conceptually different from a universe proposed by some theorists in which time always runs in the same direction and the universe expands, contracts to a "Big Bounce" and then expands again. Like the Big Bang cosmology, there is a point in time which is special and maybe even singular. But, unlike the Big Bang cosmology the other side of the Big Bang at t<0 exists, even if it may not be accessible because the Big Bang event forms an event horizon which cannot be crossed just like the event horizon of a black hole (unless space-time has non-local connections in which case wormholes from our universe to the antimatter universe and back could exist, at least at the Planck or fundamental particle scale).

Using this framework, it would probably even be possible to figure out the energy scale and properties of a simple set of high energy physics rules consistent with the Standard Model that would produce the right baryon and lepton number and global charge neutrality of the universe from the known total amount of matter-energy in any time-like slice of the monoverse with sufficient rapidity (although the immense matter-energy density of the Big Bang era would make time seem to place much more slowly to observers in the first seconds of the universe).

The charge neutrality part would be the trick and might end up linking B and L although not in a B-L conservation manner, because a single pair production crossing the t=0 boundary wouldn't naturally conserve charge. Then again, if the charge division in each pair production was random and we were talking about a number of pair productions equal to the aggregate B+aggregate L of the universe, the difference between perfect charge neutrality, and statistically average charge neutrality for a B+L number of binomial trials might be impossible to detect in practice since it would be so close to zero even if not exactly zero.

None of this, of course, would have to contradict existing Big Bang cosmology at all. It would simply fill in some blank spots upon which existing Big Bang cosmology is silent in a manner that provides a plausible explanation of why things like matter-antimatter asymmetry exists in our universe. Inflation theories and lamdaCDM, for example, would be totally unaffected by this extension of the Big Bang cosmology.

Last edited: Jul 28, 2015
21. Jul 28, 2015

### Staff: Mentor

Can you give a reference for this possibility? You appear to be basing it on "antimatter is just matter moving backward in time", which is not a good heuristic on which to base a cosmological model. (Yes, Feynman said it, but what Feynman meant by it is not going to help you in this case.)

22. Jul 29, 2015

### ohwilleke

I make no claim of originality, and also make clear that this is a subject upon which there is no scholarly consensus one way or the other in the field.

1. Sean Carroll and Jennifer Chen discussed many of the same basic concepts in their 2004 paper entitled "Spontaneous Inflation and the Origin of the Arrow Of Time" http://arxiv.org/abs/hep-th/0410270 which was the main basis for a 2008 article by Sean Carroll in Scientific American magazine ("Does Time Run Backwards In Other Universes?"). The abstract of the 2004 paper concludes by noting that "An important consequence of this picture is that inflation occurs asymptotically both forwards and backwards in time, implying a universe that is (statistically) time-symmetric on ultra-large scales.", which is discussed in the body text of the article at pages 27-28 (based on a lot of discussion of the Second Law of Thermodynamics as an arrow of time earlier in the discussion). Neilson pursues a similar approach in a 2005 paper. http://arxiv.org/abs/hep-th/0509205

Another articulation of the same basic concept is set forth by Trevor Pitts in a 1998 paper http://arxiv.org/abs/physics/9812021 See also on the emergent nature of the directionality of time Mersini-Houghton (2009) http://arxiv.org/abs/0909.2330 and discussions by Augirre and Gratton of pre-Big Bang theories generally http://journals.aps.org/prd/abstract/10.1103/PhysRevD.67.083515 and Schulman who considers the possibility that parts of the universe have an opposite arrow of time due to thermodynamics http://journals.aps.org/prd/abstract/10.1103/PhysRevD.67.083515

Another fairly similar hypothesis is explored by Barbour, et al in (2013) http://arxiv.org/abs/1310.5167 and (2014) http://arxiv.org/abs/1409.0917 A 2015 paper by Barbour then links this to entropy. http://arxiv.org/abs/1507.06498

There is also a discussion of a similar idea at https://books.google.com/books?id=QqyHUifdD6QC&pg=PA214&lpg=PA214&dq=backward+time+antimatter+big+bang&source=bl&ots=BpMvhO2J7w&sig=DvgZsLivgbpu8GkmCgDZJYFL0zQ&hl=en&sa=X&ved=0CCsQ6AEwAjgKahUKEwjp1vez1f_GAhWMnIgKHSmoD1I#v=onepage&q=backward time antimatter big bang&f=false
Nine Crazy Ideas in Science: A Few Might Even be True
By Robert Ehrlich (Chapter 10, Page 214), referencing "Gott".

Gott is associated with the notion of closed timelike curves in space. http://arxiv.org/abs/gr-qc/9404065 but some of his ideas are relevant to the directionality of time in GR.

I am sure that this anthology is not comprehensive.

2. The concept that I call a "monoverse" is one more commonly called in the literature "Einstein's block universe" or the "block universe", terminology attributed to William James. Einstein articulated the concept, for example, in his book Relativity (1952):

See, also e.g., http://philsci-archive.pitt.edu/2408/1/Petkov-BlockUniverse.pdf Physicist Sabine Hoffenfelder discusses this article (and basically agrees with it) at her physics blog Backreaction http://backreaction.blogspot.com/2008/05/block-universe.html

3. The notion of antimatter as ordinary matter going backward in time often attributed to Feynman actually originated with Ernst Stueckelberg in 1941 in the paper: Stueckelberg, Helvetica Physica Acta, Vol.14, 1941, pp.51-80 (applying the concept to positrons and electrons). Stueckelberg was also the inventor, in 1938, the the law of conservation of baryon number, the same year that he proposed an early version of the Higgs mechanism. He co-discovered the renormalization group in 1953. The recently passed physicist Nambu (originator of color in QCD and the Nambu-J-L propogator) also described the theory with approval in 1950. http://physics.stackexchange.com/questions/391/is-anti-matter-matter-going-backwards-in-time John Wheeler also explored the idea in depth and seriously http://listverse.com/2010/11/04/10-strange-things-about-the-universe/

4. Why devote so much attention to an approach that has received only a smattering of scholarly attention?

* Laboratory and astronomy evidence increasingly disfavors the leading theories of baryogenesis and leptogenesis. There is simply no evidence whatsoever for violations of the laws of baryon number conservation and lepton number conversation in the face of very rigorous searches, and the Standard Model rules out those phenomena except for sphalerons which aren't sufficient to produce baryon asymmetry to the extent observed and theories like SUSY which once offered a baryogenesis solution are looking like losers.

* The necessary alternative to B and L number violation is an initial condition that is not zero. No rule of physics can mandate the initial conditions of the universe, although one can motivate scenarios that explain it.

* Arrow of time evidence as a fundamental law of nature as opposed to emergent from entropy in a manner that can go in either direction is pretty weak.

* The assumptions are mostly quite conservative. Yet, it explains unsolved problems in physics with no other good answers. Baryongenesis and leptogenesis through pair production across t=0 is consistent with Standard Model physics, something that almost no other solution to those problems can say.

* The theory has "soft boundaries" that make it impossible to "fall off the edge of the world".

* No recourse to the anthropic principle is required.

* Key sub-concepts have been bouncing around for a long time among respected physicists.

Last edited: Jul 29, 2015
23. Jul 29, 2015

### slatts

Thanks very much for the bibliography.

If I wasn't already so amazed at being in a Very Special place that started at a Very Special time (I call it "Everyone's Pre-Conception Day", which of course has seniority even over their birthdays), I'd be even more amazed that you live in Denver, where my avatar lives.

His voice-mail-only line's 303-936-0071. (To protect PF from liability in case the address is traced out and scraped to its foundation by an angrily frustrated mob of physics students, I should point out the fact that both my avatar and my superpositioned self have read the Forum's forummal advice against giving out personal information.) He'd be interested in your take on my July 10 post in the cosmology thread "Cosmic Inflation", which has probably drifted far enough off-topic already.

Or, you might see him at the Bernie Sanders meeting at Sanora's café near Colfax & Downing, where he (as uninterested in politics as myself) is being dragged by some Commie friend, at 5 PM today.

Last edited: Jul 29, 2015
24. Jul 29, 2015

### Staff: Mentor

Yes, but this model does not say that the "backwards" portion of the model contains antimatter, and it certainly does not use the idea of antimatter being matter "moving backwards in time". Neither do any of the others you reference, as far as I can tell.

The actual physics here is not that antimatter is "matter going backwards in time". It is that, for any particle, there is an antiparticle which is the CPT conjugate of that particle. This is a subject where you really need to look at the math, not ordinary language pop science descriptions, even when the ordinary language descriptions come from physicists in the field. Ordinary language simply cannot properly describe this.

The listverse article, in particular, is just confused. For example, it says:

"This led to the idea that antimatter is just ordinary matter going backwards in time, which would explain why antiparticles have an opposite charge, since if an electron is repelled while going forwards in time, then backwards in time this becomes attraction."

This is simply wrong. Repulsion going backwards in time is still repulsion. For example, consider two negative charges which are at rest with respect to each other at some instant. If we evolve things forward in time, the charges move away from each other. If we evolve things backward in time, the charges...move away from each other in the backwards in time direction. If we look at that part of the scenario in the forwards in time direction, we see the charges moving towards each other, but slowing down, until they come to a stop at some instant--i.e., they are repelling each other.

25. Jul 29, 2015

### ohwilleke

I'm not going to defend the listserv which I referenced solely for the proposition that John Wheeler shared the views of Feynman, Stueckelberg and Nambu on the subject.

I've looked at and understand the math (I was a mathematics major with a fair amount of undergraduate physics in college). There is more than one way that you can articulate and assign meaning to what the math says.

The interpretation of antimatter as matter going backward in time, and the interpretation of antimatter being a CPT conjugate particle that goes forward in time are both perfectly consistent with the math which does not contain an arrow of time.

We feel compelled to assign an arrow of time by English grammar which makes verb tense distinctions based upon time sequencing, and not by the mathematics which requires us to assign an arbitrary direction of time for booking purposes but does not functionally depend upon the time coordinate system used (in the absence of W boson interactions where there is a CKM violating phase in which a CP flip produces a corresponding T flip). The verbal description we assign to a particular Feynman diagram in an event involving antimatter is very different between the two interpretations, but the diagram itself is the same and is independent of the simplified one dimensional space-time coordinates used. Rotating a Feynman diagram changes the verbal interpretation, but not the physics.

Would this really happen as I have suggested? It is hard to say. Pretty much all speculation about physics in the era of baryongenesis and leptogensis is beyond the domain of applicability in which any of the laws of physics have been tested. Hell, no one has ever even observed a sphaeleron event, which should happen with predictable frequency at about 140 GeV (with appropriate unit adjustments) of temperature. The case that the arrow of time is driven exclusively by entropy (which the CKM CP violating phase making a distinction between one direction or the other without expressing a preferred direction), is certainly plausible as the literature indicates, in which case a universe in which time flows backward from the Big Bang works.

It would be possible in this scenario to interpret the pre-Big Bang period in such as scenario as a rushing of all the matter in the universe towards the Big Bang, and Barbour has shown with his numerical models that physics makes that possible, even if that is a somewhat unnatural way to describe what is happening.

Is an extrapolation of a notion shared by four of the fathers of 20th century physics into an area beyond the domain of applicability of any laws of physics we have today in order to explain the vexing problem of the baryon asymmetry of the universe a stretch? Perhaps. But, it is really a far more conservative hypothesis than the vast majority of inflation theories (several hundred of them) and baryongenesis/leptogenesis theories, all of which require new particles and forces for which we have absolutely no experimental evidence merely because they could solve a phenomenological problem arising from the mere beauty based belief that the Big Bang should have equal quantities of matter and antimatter.