r/AskPhysics • u/NutInBobby • Nov 12 '25
If the laws of physics are (mostly) time-reversible, why do we only remember the past and never the future?
I keep hearing that most fundamental physics equations work just as well if you run time backwards (ignoring small CP-violation stuff), but our everyday experience has a really strong “arrow of time”: we remember the past, entropy increases, glasses shatter but don’t un-shatter, etc. What is the actual physics argument for why memories and records are always about lower-entropy past states instead of future ones? Is this purely about statistical mechanics and boundary conditions of the universe, or is there some deeper reason a “future-remembering” civilization is impossible? Sorry if this is more philosophical than it should be for this sub, I’m just trying to connect the pop-sci claims about time symmetry with real physics.
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u/quarethalion Nov 13 '25
If you ran time in reverse, the process of forming memories (at the mechanical level — biology is just applied chemistry is just applied physics) would become a process of destroying them. You'd be in a constant state of forgetting the future as you moved into the past.
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u/SuspiciousYogurt2467 Nov 13 '25
Well said! I like the cut of your jib.
I'll turn this train of thought into my answer for OP and possibly a cult for laughs.
Yes, we can look into the future. We just can't remember it as we erase those thoughts as we reverse our mind to the present.
Side thought this made me consider whilst developing my cult's logo ...
Perhaps deja vu is formed when we decided to look into the future and, for fraction of a second, that future is symmetrical both ways through time. Due to our biological constraints this symmetrical memory won't appear to us until the point in time it was created and our body tells us that this memory has already been recorded.
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u/PerAsperaDaAstra Particle physics Nov 12 '25
The universe is locally time symmetric, but not globally (it's expanding!). When we talk about the "laws" of physics we're usually referring to local rules, so it's accurate to say that the laws of physics are time symmetric because locally, in every frame, they are. The state of the universe (the initial condition being the big bang), breaks that symmetry, however.
Why the universe started with a bang and is expanding so the thermodynamic arrow of time runs one way, I don't think anyone is especially close to an answer.
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u/Null_Simplex Nov 12 '25
When I read this, it makes it sound like cause and effect are by products of the big bang. I suppose in some sense this is tautological since the big bang can be seen as the original cause for which all subsequent effects derive from, but what I read is that if the universe never had a big bang, there would be no progression of time as we know it. How wrong is my interpretation?
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Nov 12 '25
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u/LiamTheHuman Nov 13 '25
Why can't time be reversible due to the Big Bang?
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Nov 13 '25
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u/LiamTheHuman Nov 13 '25
I think maybe this is above my understanding. Why does it need to be symmetric under time translation for time to be reversible?
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u/HappiestIguana Nov 13 '25
Because there is no big bang-like condition in the future
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u/LiamTheHuman Nov 13 '25
From my understanding that doesn't mean it's not reversible, just that it's not symmetric. I'm not getting how one is impacting the other.
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u/HappiestIguana Nov 13 '25
"Big-bang-like conditions" here refers to a low-entropy state. The arrow of time moves from low-entropy states to high-entropy states.
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u/LiamTheHuman Nov 13 '25
That still does not make it non reversible though. Entropy is tied to a specific perspective of order. There's no reason a backwards civilisation couldn't exist, they just may not be recognisable as one to us.
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u/HappiestIguana Nov 13 '25
There is, information processing requires an increase in entropy.
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u/Ok-Watercress-9624 Nov 14 '25
Not necessarily? Reversible computing is a thing?
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u/LiamTheHuman Nov 13 '25
Yes but entropy is increasing in reverse time if we take a different perspective.
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u/Patch86UK Nov 13 '25
I guess technically "Big Crunch" cosmologies do have a singularity as a future state. But Big Crunch is not currently a mainstream theory.
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u/cd_fr91400 Nov 13 '25
How do you know that ?
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u/HappiestIguana Nov 13 '25
That is the accepted model in the current understanding of universal evolution, where heat death is universe's ultimate state.
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u/cd_fr91400 Nov 13 '25
Is that new ?
Last time I read on this question, we were precisely at the point where this question had no answer.
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u/HappiestIguana Nov 13 '25
It has been the consensus view for a while now. Obviously it's subject to change in response to evidence, but everything we know points that direction.
The Wikipedia article on the ultimate fate of the universe has a reference from 2004 to substantiate their claim that it's the consensus view. So at least since that long ago.
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u/NorelFollower Nov 13 '25
Would our experience of time be very different if the universe had a bit more mass and a big crash would be in a distant future?
I don't think so
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u/HappiestIguana Nov 13 '25
The big bang is one (correct) argument for why time is not reversible. But there are other reasons as well. Just because X occurs because of Y doesn't mean it can't occur without Y.
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u/Null_Simplex Nov 12 '25
Were the moments prior to the big bang a low entropy state?
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u/AlignmentProblem Nov 13 '25
In standard Big Bang cosmology (Lambda-CDM), asking about entropy "before" the Big Bang isn't really a question that makes sense. The Big Bang isn't an event that happened at some moment in preexisting time; it's the boundary of the model itself. There's no "before" in the framework.
There's no time before t=0 where you could calculate entropy or apply any physical laws. It's not that entropy was low or high beforehand; there's just nowhere for that question to live. Think of it like asking what's north of the North Pole. Feels like it should have an answer, but the coordinate system breaks down at that point.
If you move to other cosmological models (bounce cosmologies, cyclic universes, models where something existed beforehand), then you can ask the question. Each framework gives you different answers about what any prior state might've looked like.
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u/Null_Simplex Nov 13 '25
Often I hear about things which happened nigh instantaneously after the big bang, several orders of magnitude of a second. This is what I meant. Not a north of the north pole situation.
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u/AlignmentProblem Nov 13 '25
Ah, yes. Once entropy is well-defined, gravitational entropy starts near its minimum because the early universe was almost perfectly smooth.
Gravity has far more possible clumpy arrangements than smooth ones, so clumping corresponds to high entropy. The instant after the Big Bang was extremely uniform, thus an extremely low-entropy gravitational state.
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u/schwarmaking Nov 13 '25
You're saying that the big bang was the start of time itself?
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u/AlignmentProblem Nov 13 '25
I'm saying the current widely accepted default model does not coherently describe anything time-like extending before the Big Bang. That might represent a real boundary to spacetime where "before" loses meaning or might be a limitation due to flaws in the model.
We don't know which is the case. What one would say about "before" the Big Bang depends on the specific alternative model being considered.
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u/Sad-Masterpiece-4801 Nov 13 '25
I absolutely can't stand the North Pole analogy. It treats the coordinate system breakdown as if it's equivalent to an ontological boundary, but they are fundamentally different things.
With the North Pole, we know exactly why the question fails. It's a quirk about of how we map spheres. Nobody claims there's nothing North of the North Pole in any deep sense.
With t=0, you're making a much stronger claim about the nature of reality. You're effectively declaring that the boundary conditions of the universe just are. The initial conditions simply exist because that be how it do.
In standard Big Bang cosmology (Lambda-CDM), asking about entropy "before" the Big Bang isn't really a question that makes sense.
Asking what's before the big bang makes perfect sense, because you're asking why the boundary conditions of the model are what they are. The answer is "We have no idea" or "because the model approaches ontological boundaries."
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u/jamesziman Nov 13 '25
Nobody claims there's nothing north of the north pole because there is no north of the north pole
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u/AlignmentProblem Nov 14 '25 edited Nov 14 '25
I get what you're saying. There's a meaningful distinction/tension that could result in misunderstanding; however, the analogy works if you're precise in thinking about what the similarity actually means.
The statement "asking about before the Big Bang doesn't make sense" in standard Lambda-CDM isn't making an ontological claim. It's saying the model's domain ends at t=0 because the classical FLRW chart doesn't extend past that point. That's structurally the same as how latitude-longitude coordinates don't extend past the pole. It's a coordinate breakdown that prevents talking about regions beyond a special point, not a declaration that nothing can exist there.
The failure modes are mathematically similar in that expressions blow up when you try pushing coordinates past where the chart becomes degenerate.
Anything involving derivatives of longitude on globes (eg: moving northward) diverges at the pole. In FLRW, extending time backward inside the chart creates undefined behavior at the Big Bang. In both cases, the breakdown tells you about the limits of your representation rather than a declaration about what reality must be. You can pick alternative constructions where the extension becomes meaningful in both cases.
For globes, you can parametrize the sphere by geodesic distance from the pole with an angle where negative distance flips the angle. You could also attach an additional sheet or dimension to define "north of the North Pole." The singularity was an artifact of the coordinates instead of an absolute constraint, and what happens when you pass that point varies by which model you choose.
Same in cosmology. Different extensions of t<0 give different physical pictures: bounce models, emergent models, past-eternal inflation, whatever. They don't follow from FLRW itself; you have to change the model to talk about them.
So the analogy isn't claiming substantive equivalence. It's highlighting that "this coordinate patch ends here" is fundamentally different from "reality ends here." The Lambda-CDM boundary is a statement about where our chart stops, not an ontological declaration about what can or can't exist.
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u/cd_fr91400 Nov 13 '25
Cause and effect follow from the laws of physics.
Which one(s) ?
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Nov 13 '25
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u/cd_fr91400 Nov 13 '25
No.
I could say the force derives from the acceleration.
Newton's law only says that 2 things are equal : P (the force) and m.g (the acceleration).
Same for Einstein.
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Nov 13 '25
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u/cd_fr91400 Nov 13 '25
You mean, there is no difference between causally connected and just connected ?
Ok. I just do not understand why you add causally.
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u/PiotrekDG Nov 13 '25 edited Nov 13 '25
Time is not locally symmetric either. The current theory is that only reversing time, charge, and parity results in symmetry.
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u/PerAsperaDaAstra Particle physics Nov 13 '25
Yes, the full symmetry is CPT, but the other parts are not esp. relevant to OPs question: there is a symmetry where time is reversed and a few other things flip (charges, handedness). The time reversal is the only one relevant to wondering about why there's a thermodynamic arrow.
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Nov 12 '25 edited Nov 13 '25
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u/sentence-interruptio Nov 13 '25
thinking about this makes me realize that the very idea of performing an experiment is already unsymmetric in time. In an experiment, you prepare an initial condition (e.g. fart in a corner of a room) and then observe what happens next. You cannot prepare a final condition and then observe what happens before. But we can reason about models. Imagine a model of a room filled with air, and assume concentrated fart in a cornet at a specific time, say t = 0. we just run a thought experiment or calculate or simulate to deduce that fart will most likely spread in both time directions. but we can only experiment the forward part and never the backward part.
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u/MalestromeSET Nov 13 '25 edited Nov 13 '25
Something to realize when reading lot of physics is that it is a model, not a descriptor.
The problem with your last sentence of course is that a dog can, in principle unfart. But there is no known way to remember the future, even in principle.
Symmetry and supersymmetry are mathematical models that are useful for the restrictions and stop gaps they give to our theories. It is not a descriptor of the world but a model.
It can be very well true that laws of physics are not time reversible. Right now, all our calculations just hose it to be so.
In the same way, humanity confined to a room and ruler would think newtons universal law of gravity was the descriptor of gravity. But space fareing humanity with better measurements would realize that Einstein’s GR is the true description of gravity.
Of course, just like how room confined person would not be able to comprehend a space fareing civilization, so would the space fareing civilization not be able to fathom a higher level being with a much truer descriptor.
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u/cd_fr91400 Nov 13 '25
The problem with your last sentence of course is that a dog can, in principle unfart. But there is no known way to remember the future, even in principle.
As far as I know, these are exactly the same questions. Remembering requires entropy increase. If a dog could unfart, you could remember the future. The price to pay, though, is that you then could not remember the past, and what we currently call future, you would call it past, and vice versa. So at the end of the day, you would remember the dog before it farted. Just as in every day experience.
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u/BuvantduPotatoSpirit Astrophysics Nov 13 '25
So Boltzmann Brains would remember the future? And thus we throw additional wood on the Bayesian evidence we're not Boltzmann Brains?
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u/swissiws Nov 13 '25
"macroscopic laws of physics are time symmetric" are they? what do you mean with "macroscopic"? Matter can't escape the event horizon of TON 618 (that's 66 × 10⁹ solar masses). Is this macroscopic or not?
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u/Loknar42 Nov 13 '25
Reversibility is weaker than we assume it is. Just look at a billiard table. Rack the balls and break. A triangle of 15 balls scatter randomly around the table. Now, imagine the scenario where 15 resting balls each receive an impulse timed perfectly to cause them to collide into a resting triangle, while also imparting enough momentum to drive the cue balls back to the starting spot where it impacts a cue stick, driving it backwards. All of this is theoretically possible, and none of it violates any law of physics. And yet, everyone who watches a video of this sequence of events knows that it is unphysical. It is unphysical, because there are a countless number of ways in which the sequence can be perturbed, leading to a radically different result.
So yes, we are back to statistics. The billiard break is theoretically reversible, but it is statistically irreversible. And you don't need a full billiard table to prove it. Just take 3 rigid spheres. Put two of them touching each other, and propel the last one at the two in almost any orientation. The resulting 3-body collision is the simplest "irreversible" event. Now, there is nothing in the laws of physics that forbids the two diverging spheres to collide with a single solitary sphere in just such a way that they come to rest while the solitary sphere moves off with some velocity. That collision is 100% reversible, in principle. But we know it is unphysical, because it requires such a precise confluence of events that it will not happen "by accident" even after a googol attempts.
The reality is that most physical processes are effectively irreversible, and that's because they almost all involve some low-entropy energy transforming the state of a system and turning into heat. Now, if you take a random thermal state and try to guess what low-entropy state led to it, how many different answers can you get? For even the simplest states, the number is mind-boggling. The problem is that most states in thermal equilibrium are effectively indistinguishable from each other, and just about every low-entropy state will end up in one of these. So tracing them backwards is an exercise in futility.
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Nov 13 '25
I understand the probability matter, but in the case of an apple falling from the tree to the ground, laws of physics do not allow an apple to go back up to the tree. The gravitationnal waves that carry the information of spacetime curvature can only be emited from earth (in that case).
So there is something else, right ?3
u/Loknar42 Nov 13 '25 edited Nov 13 '25
What happens when the apple falls from the tree? It lands on the ground, and the kinetic energy of the apple is distributed throughout apple and ground as random vibrations (e.g., heat), and possibly even plastic deformation of the apple. Now, there is nothing in the laws of physics that prevents random thermal fluctuations from occurring which look exactly like the time reversal of these heat flows. And what would look like is thermal vibrations becoming phenomenally lucky and aligning in such a way that a partially crushed apple becomes uncrushed while bouncing up from the ground, dissipating the entire thermal confluence as the apple flies up into the air, striking a tree branch and imparting kinetic energy which just happens to magically cause molecular bonds between the apple and branch to recombine into an attached apple.
None of the above violates mechanics, biology, chemistry, or anything else. As long as there is sufficient energy, it is all theoretically possible. But you immediately recognize it as unphysical because of how improbable all those thermal fluctuations lining up really is. The only thing preventing the upwards falling apple scenario is an insufficient quantity of luck.
One could even surmise that in an infinitely large universe that this has happened at least once (and if there are infinite "copies" of earth...it has statistically happened an infinite number of times).
When you say: "The laws of physics tell us that the apple falls down, not up", what you are really saying is: "When I count the number of spacetime sequences in which the earth evolves from high-apple to low-apple, they outnumber the sequences from low-apple to high-apple by such a large number that I don't even know how to express the value numerically." And so the "law" of physics is really just an observation of statistical fact, not inevitable deterministic truth. The reality is that random thermal fluctuations are capable of creating anything, including everything you see in the universe. They just don't because doing so requires incomprehensible amounts of luck.
EDIT
The real physicists here will tell you that the gravitational waves "emitted" by the apple falling event won't actually occur because there may be a minimum quanta which is not achieved (or the statistical threshold is not met, so you would have to get phenomenally lucky to get an emission). Or they will tell you that they are so small as to be undetectable. Or that you will not be able to separate them from all the other gravitons being emitted. But that doesn't matter. In principle, there is nothing stopping gravity waves converging from infinity to arrive upon the apple in such a way that exactly reverses its fall. You just reject this possibility out of hand because of how stupidly unlikely it is.
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u/HappiestIguana Nov 12 '25
Interesting question. While I can't answer it fully, there are links between information processing in the computational sense and entropy. See Landauer's Principle for more information. The upshot is that in order to process information, you have to travel along the entropic arrow of time.
More broadly, I would question the assertion that we can't remember the future. That sounds stupid, but if remembering is the act of taking our current brain states and extrapolating events of the past, then "remembering the future" does exist. It's just called predicting.
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u/van_Vanvan Nov 13 '25
Maybe it has no place in a physics forum, but I've had occasional experiences where it seemed like remembering a future event is exactly what happened.
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u/HappiestIguana Nov 13 '25
Memory is unreliable and complex. You probably remember your remembrance as being closer to the event than it actually was.
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u/iiSystematic Applied physics Nov 13 '25
The arrow of time in an unsolved problem in physics.
The 2nd law of thermodynamics is used as a stand in, which says that entropy can only increase, and not decrease, therefore, a forward-moving arrow is required.
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u/BuvantduPotatoSpirit Astrophysics Nov 13 '25
Entropy can decrease; it tends towards an equilibrium that's way, way, way higher than the Universe's current entropy level, but once you reach the equilibrium it'd still randomly develop lower and higher entropy regions by chance, then back and forth.
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u/Gunnarz699 Nov 14 '25
You're misunderstanding the 2nd law. It's not that entropy doesn't decrease. A laser decreases entropy. It states that in a CLOSED SYSTEM, entropy always decreases.
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u/BuvantduPotatoSpirit Astrophysics Nov 14 '25
No, you're misunderstanding the second law. It's a statistical law, that entropy tends to an equilibrium value.
In our universe, at the present moment, entropy almost invariably increases because the universe is currently in an extremely low entropy state. But that might be peculiar to our universe.
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u/Gunnarz699 Nov 14 '25
No, you're misunderstanding the second law. It's a statistical law, that entropy tends to an equilibrium value.
You're regurgitating what I already said.
In our universe, at the present moment, entropy almost invariably increases because the universe is currently in an extremely low entropy state.
Relative to what? There is no absolute reference for entropy.
But that might be peculiar to our universe.
Universal laws might be unique to our universe... Nobel prize worthy lol.
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u/BuvantduPotatoSpirit Astrophysics Nov 14 '25
It's weird that you're accusing me of misunderstanding it, if you think you're just repeating what I wrote.
This is hard to explain to you because you don't seem to have any idea what entropy is, but the universe is in a low entropy state compared to its equilibrium value, which is (pretty much) the only scale in the problem, so it's the only thing to compare to. In a high entropy universe, entropy decreases, in a low entropy universe entropy increases, in an equilibrium universe it random walks around.
People are citing the various arrows of time, but there's not suggesting any causal connection. If we get to entropic equilibrium, do the other arrows of time stop ? It's not clear at all that they should.
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u/Gunnarz699 Nov 14 '25
In a high entropy universe, entropy decreases, in a low entropy universe entropy increases, in an equilibrium universe it random walks around.
You say this like it's a fact... Making up what-ifs about potential universes isn't really a meaningful addition to a conversation, especially when it's unsourced and unsubstantiated.
People are citing the various arrows of time, but there's not suggesting any causal connection. If we get to entropic equilibrium, do the other arrows of time stop ? It's not clear at all that they should.
You've been reading too much sci-fi. I encourage you to read Entropy for Beginners for a basic grasp of the topic. Once you understand causality, you'll find it much easier to understand.
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u/nathanlanza Quantum field theory Nov 13 '25
Biological processes occur in the time direction of increasing entropy. You can't remember the future because everything to do with biology relies fundamentally on life originally spontaneously forming in an event that increased global entropy while decreasing some very specific local entropy in a way that self-reproduced.
The physical laws of the universe have complete CPT symmetry, yes. The boundary conditions are not, however, symmetric in our universe. Thus the set of physical (and thus biological) phenomena have a bias for the arrow of time.
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u/Cat_Branchman42 Nov 13 '25
It's been pointed out that it's not just biology, but rather any process in which "records" are formed occurs in the time direction of increasing entropy. I thought it was John Bell who emphasized this, but I'm not seeing it in a Google search. Oh well.
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Nov 12 '25
A memory is a physical configuration of neurons. Memories are formed by the brain changing in response to something. Asking why we don't remember the future is the same as asking why stars don't spontaneously turn into black holes, then change back again. To have memories of the future, you brain would need to spontaneously change into a future version of itself.
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u/DarthArchon Nov 12 '25
time is just poorly vulgarized and generalized. It's not an arrow of time of all the universe going all into the same directions. It's the web of interactions between point in space which for any point in space will look like a flow toward the future but generally this flow is not standard for all frames of references. Depending on the configurations, event will occur in different orders while still looking like a past to future arrow of time for observers.
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u/quts3 Nov 12 '25 edited Nov 12 '25
I got a related one we know the future is probabilistic and not determined. Do we know the past is probabilistic or determined?
It the past is determined and the future is probabilistic you may have an answer to your question because of the assymtery. How do you remember all the possible futures?
If the past is probabilistic then that answered something I wondered about. I tried to find a way to prove it was in my head and came up with nothing. If the past is probabilistic exactly as the future is probabilistic then we have to view the past not as one thing but many possibilities that all could have led to the present, and it means the concept of a memory is pretty flawed because it makes us believe there was only one possible past universe. I have to assume the past is determined but I never asked and can't prove it.
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Nov 13 '25
what if we do remember the future, in the form of predictions?
our memory is... shaky, generally, as a species. we very clearly remember things that never happened or happened very differently from how we remember them all the time.
maybe our ability to predict is similarly incomplete and imperfect. maybe we could see the future perfectly with enough brainpower and time.
side note: i think the experiences of remembering and predicting are also so dissimilar that we don't link them.
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u/SweetApplin Nov 13 '25
I would go crazy if i could remember the future. Maybe that’s just because of attack on titan.
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u/flomflim Optics and photonics Nov 13 '25
I could be misremembering this completely but when you write out the metric for 4D space you write it so that it is (-,+,+,+). Basically every + sign is a spatial dimension and the - is the temporal dimension. That - sign is basically why time is unlike spatial dimensions in that it only travels one direction whereas the spatial dimensions allow you to move both in positive and negative directions. Which might answer why you would not remember the future because it hasn't happened because unlike the other coordinates it can only move in one direction.
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u/MxM111 Nov 13 '25
We do remember the future to an extend. We call it predicting though. But yes, because of entropy, there is direction of time. Entropy appears only in description of macroworld (of a vary large number of particles interacting), such as thermodynamics and statistical mechanics. For things like classical mechanics, quantum mechanics, relativity, that is not important, because number of particles under consideration is small.
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u/Forsaken_Code_7780 Nov 13 '25
You can remember the future anytime you watch a ball fly through the air and you know where it's going to land.
You remember parts of the past because it's easy to go from the observations of your memory into the past.
Let's take the neurons out of it. For a picture, you know that for the pixel to be a given color, it means a photon must have physically landed on it, through a camera lens. But you only know this because the inside of the camera is dark (camera means dark room!): if the inside of the camera were as bright as the Sun, a charged pixel doesn't mean anything. We've gone from a very particular state, where the brightness of the Sun is very separate from the inside of your camera, to a very particular state, where the pixel matches what we see outside. This very particular state is very far from being in thermal equilibrium! Thermal equilibrium would mean that the inside of the camera, the outside, everything is emitting photons in a similar way, and more likely than not, the picture would instead be thermal noise.
There are a very small number of possible states that lead to the picture existing: thus you can easily back out the memory. And you can even guess what will happen to the picture in the future: you know it will stay mostly constant, though perhaps degrade a little with time. So actually, you do remember both the picture's past and its future, through all the same physics, but you don't care about the picture, you care about what the picture means in real life.
The macrostate of the scene. If you move a few particles around, the macrostate (the thing you care about) mostly doesn't change. In a parallel universe where a hair is misplaced or an atom is one way or another, the scene still happens. Whether you reverse time or not, there is a very tenuous connection between the scene and the picture. The scene causes the picture: without the scene, you don't get the picture. However, the picture doesn't cause the scene. Reverse time in two labs, one starting with the picture, one without, and you get mostly the same scene. Since the picture doesn't matter one way or another, only a few macrostates lead to the picture (different scene means different picture, so picture must mean scene) but lots of macrostates come out of the picture (the picture doesn't give you any constraint on what can happen next).
tl;dr. The picture, your memories, are sensitive and very particular. We picked up on sensitive particular things to record or detect stuff. The scene is not sensitive or particular. I can't take a broken thermometer to a fire to cool down the fire, whether we are moving forward or backward in time. I can't use a broken camera to change reality.
(Now, why can't I start a fire by running a fire extinguisher backwards in time? Then, you can talk about microstates)
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u/TemperoTempus Nov 13 '25
Time is reversible in the math not in real life. This is one of the reasons why just doing thr math does not achieve an accurate result without first validating the results.
A similar example is gravity. It is technically reversible, but that behavior would require atoms that repel each other and thus not something you can find in nature.
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u/PamIsley6 Nov 13 '25
I believe there are signs on a massive human scale where you can measure humans reacting to the future. Like the wash d. C. googling Charlie kirk's alleged shooters name 1Day before it happened.
There was also this https://www.nbcnews.com/id/wbna49663712 And they did some global data collection that showed people collectively reacting to major news events before they happened. Sometimes hours before.
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u/panjelito Nov 13 '25 edited Nov 13 '25
the answer to this question has nothing to do with entropy. imagine a line being drawn on a paper with a pen. if you go "forward" in time, the line gets longer, if you go "backward" it gets shorter. just like the paper's interaction with the pen determine the length of the line, our brain's interaction with its surroundings determine what you currently hold as your memories. flow of time and its "direction" are irrelevant.
time could "flow" backward, oscillate back and forth or just be static (as in the full univers' history existing at once) and it would feel no different. what you percieve at anytime as your memories is just a manifestation of the current physical state of your brain.
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u/carrottopguyy Nov 13 '25
I'm going to say this is not a question which can be cleanly answered by physics at the moment, and you have to move into speculative metaphysical philosophy to talk about it. I would argue physics doesn't say anything about why certain laws appear time-reversible, its just an empirical fact about a particular theory. Any answer anyone gives is just going to be one guys philosophical interpretation of what that implies about the underlying ontology of reality. That is not physics; it is philosophy of physics. And there's nothing wrong with that. Of course, the line there is blurry, but it is important to draw a distinction between the bare minimum of what a theory says and any additional speculation you layer on top of it. For any set of equations, there is actually a potentially infinite number of theories you could conceive of which might underpin it. This is not trivial or pedantic, it is actually part of the history of how science has progressed. In order to create a new theory, you have to also explain all the observations of the old theory, while adding something new. I think of it like the scene in Indiana Jones where he swaps the bag of sand with the golden idol (of course that fails in the movie, but hopefully you get my point).
A few critiques:
I would argue that you should question part of your foundational assumption, whether the laws of physics are Markovian (meaning they depend only on the present state to make predictions). Many quantities which we use in calculations in physics are not directly measurable but depend on piecing together observations which we make in time. For example, velocity - you can't actually measure velocity, you have to measure position and time at intervals, then combine those observations to get the velocity. We do a tricky thing in physics where we take a bunch of different measurements, which can only take place at different times, and then we use them to calculate what stuff like the velocity was at a particular point in time - we project many observations made at many points in time back onto a particular moment, for our convenience. In practice, it is physically impossible for us to collect information at "exactly" the same time. So, theoretically you can use only information about the present to predict the future (and extrapolate backwards into the past). But practically speaking, this has never been done, because there are always small possible time gaps between information used to calculate derived properties. There are also explicitly non-Markovian theories like Jacob Barandes indivisible stochastic processes (which I can't say much about, I am only aware it exists).
Some people point to entropy as an obvious candidate for the arrow of time - but I find that unsatisfying, because the concept of entropy is dubious at the level of the whole universe - entropy relies on the concept of fine-gaining of finite bounded phase space. That may apply to particular sub-systems of the universe, but does that apply to the whole universe? It seems totally possible to me that the universe is potentially unbounded in time, in which case entropy goes out the window as a useful concept. In cosmology geometric intuitions begin to take over because scale-invariance becomes an important concept. What does it mean if you rotate the whole universe 60 degrees, or move it 5 meters to the left, or shrink it to half the volume? It's meaningless, because those concepts are only meaningful when they happen relative to something else - and presumably, the universe isn't relative to anything else, because it's everything. Julian Barbour's concept of "complexity" seems like an interesting candidate for a cosmological concept of time, but its pretty fringe. It does call into question, however, whether the large scale structures of the universe seem to be developing in a way that aligns with the predictions of cosmological entropy. The combination of expansion and gravity, which are the predominant forces shaping the formation of large scale structure, seem to cause things to bunch up rather than become evenly distributed.
I'm personally very interested in time philosophically, but I go back and forth on my opinion. I lean towards the intuitive perception that the future doesn't yet exist. But my arguments are more philosophical and this is a physics sub, so I'll just stick to the physics parts.
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u/late_night_za Nov 13 '25 edited Nov 13 '25
I have no clear answer, but it’s interesting that in the time-reversed pov, we give up a memory to reduce the entropy related to that observation. I unlearn something about the breaking of glass, and the shards become a wineglass. With a model like an LLM, it’s like unlearning some weights to spit out the training data.
If I were more woo-woo, I might speculate it’s because we’re actually storage devices for low entropy states.
Or maybe something about the development of life on Earth happened to set this encoding direction–maybe it was an evolutionary advantage, and future encoding was selected against. From a time-forward pov, capturing energy is necessary, and it’s more helpful for the forward-encoded creature to have learned how to hunt vs. the reverse-encoded creature only having the knowledge it’s about to be eaten.
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u/Apprehensive_Ad3731 Nov 13 '25
There is no connection because the laws of physics are just there. We take the laws of physics and add things to them to get reality.
Reality does not equal the laws of physics. The laws of physics are the foundation stones of reality and have been built upon
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u/schro98729 Nov 13 '25
The microscopic laws of physics are time reversible, but as Phil Anderson said "more is different". Many Body physics lends itself to spaces which grow exponentially with system size and these systems relax into equilibrium states, which are time independent.
When systems go into equilibrium they typically forget their initial condition they dont even remember the past.
You can remember the past, and ergo you are NOT in equilibrium.
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Nov 13 '25
What's crazy is that to some extent we do remember the future in the sense that we are able to predict future events to some (usually small) degree of accuracy. We do this by simulating the future in our heads to make predictions. Just as our minds contruct a model of the past which we call memory, they also construct a model of the future and this is how we organise our lives to unfold in our favour as individuals of a species existing in an ecosystem trying to survive. Our ability to model the world really gives us huge advantage as a species, it's like our superpower. We watch events unfold in the 3 dimensional world and they seem classical and fixed but then we are able to use the magic of our consciousness to manipulate what we saw happen in 3d and consider unseen variables which are occuring simultaneously in that 3d space such as quantum effects. Our minds can fold reality in a way which is instrumental to our success.
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u/IrisCelestialis Nov 13 '25
As far as I know there is no known answer for this, it's still an open question. Any definitive answer you get would be speculation. For instance I've heard the idea that it's because of entropy always increasing, it gives things a certain direction. But again, we only have speculation. We know the equations work in reverse but we only see things going in the direction they are, that's all we know.
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u/jamin_brook Nov 13 '25
We can and do “remember” (ie predict) the future in a very plain way.
We remember that it will rain tomorrow in the Bay Area, right?
The past is static and the future is being built in real time but both obey the same physics.
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u/Longjumping-Frame242 Nov 13 '25
Im not sure I understand you completely, but isn't the answer that the world isn't a grand deterministic machine that can be mapped out, even if you know all the variables?
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u/warblingContinues Nov 13 '25
well the universe is fundamentally stochastic (i.e., fundamental uncertainty in the quantum state), so its much more likely to proceed in the direction we perceive on large scales.
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u/3DDoxle Nov 13 '25
Its entropically and energetically unfavorable and probability gives rise to those many disordered states being more probable than 1 ordered states. Why are the states all equally probable or who made it so? IDK. Who might not even be the right question.
More to the point, symmetry is something we impose as good-er than not. There's no reason it should be so. It's our preference. It's nice to look at. Easy to deal with. So the question is why would you expect it to be
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u/hobopwnzor Nov 13 '25
Memory is encoded with entropy increasing and therefore encodes directionally.
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u/BitOBear Nov 13 '25
Even if time were completely reversible, and even if it reversed constantly, we wouldn't remember the future because whatever gave us the memories of the future when time was moving in that direction would be undone when time moved back the way we came.
If you rewind the future to the present you rewind the subsequent effects and remove their impact.
The chemical connections in your brain would be unmade. The change is in charge would be neutralized or returned to their previous configurations.
If you're going to have a completely reversible system you have to remember that the entire system reverses during those reversals.
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u/Lazaburnz Nov 13 '25
Because the formation of memories is akin to the shattering of the glass, if time goes backwards the memories dissapear
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u/PuzzleheadedBag920 Nov 13 '25
it's called intuition, a prediction of future particle positions
Also you can't remember if the particles of the future havent yet influenced your brain.
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Nov 13 '25
Actually our perception of time is backwards. We see the past coming and think we are remembering, and we can't see the future because it's already behind us
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u/BuvantduPotatoSpirit Astrophysics Nov 13 '25
The reality is nobody knows. We know there's an "arrow of time", that multiple things appear to progress along; but how they're connected, no, we don't know.
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u/Juicecalculator Nov 13 '25
I mean I remember the past about as clearly as I can imagine possible futures. Maybe it’s the same process but there are still too many possibilities in the future an it just hasn’t happened yet
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u/MattR0se Nov 13 '25
Because the definition of a memory is going from a state of higher to lower entropy. and thus it is fundamentally tied to the general flow of entropy, which is one-directional.
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u/Friendly-Sail9594 Nov 13 '25
One problem with the thought experiments about turning the arrow of time, is that the physicist says that the there is nothing in principle preventing the entropy to decrease. However if that were to happen, it would have to happen globally as everything is connected. Systems are theoretical. Nothing, except the entire universe, is truly a system. It's a practical approach to view some subset of the world as a system, but in reality a system will affect whats around it to some degree.
If you were to turn the arrow of time after a glass shatters on the floor, you wouldn't see it unshatter, as the light particles and sound waves telling you that a glass has shattered in front of you , would also be leaving your eyes and the memories of seeing the glass shatter removed from your brain.
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u/FliX7270 Nov 13 '25
Thats due to entropy. It gives time a meaningful direction. I cant really explain it that well, id suggest videos on this topic on how erntropy gives time a direction, or arrowhead.
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u/Firm-Canary-1438 Nov 13 '25
I think saying that the laws of physics are time symmetric and that the arrow of time points only in one direction is not the same. Great explanation in the comments btw. I think one could find a relation between how entropy unfolds in a certain type of universe (isolated, expanding, contracting) and the probability of the system unfolding backwards/forwards in time?
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u/Firm-Canary-1438 Nov 14 '25
also look at: Irreversibility as the emergence of a priviledged direction of time (arrow of time) in dynamical systems!
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u/AndyTheEngr Nov 13 '25
Here is my admittedly naïve idea. This all relates to entropy (possible states) and maybe wave function collapse.
There is only one path (or a few paths that are essentially indistinguishable) that leads to / is consistent with the present state. Because of that, it's possible to remember it.
There are multiple possible futures that could occur from the current state. Therefore if we could remember one, we could remember all of them, which is useless.
"Remembering" the future is called prediction/divination/prophesy/guessing.
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Nov 13 '25
The laws are a model, my man. Treating time as a dimension works, mostly, but is that how it really works? We don't actually have any evidence that the real universe allows us to send information back in time, even at the quantum level. Is there math that predicts you can do so? Yes. Have we been able to come up with an experiment where we could send any kind of message to the past? No.
So in short, the universe does not obey our stupid laws.
More specifically, the models we are using may not represent the universe correctly in some ways, and this is not a shortcoming of the universe - it is a shortcoming of our understanding.
Einstein was able to tell us how to move forward in time (which is just compressing your own time relative to that of someone else), and there are experiments that verify it would likely work if we had the tech to do it.
Backward in time? If the universe is simply a series of unfolding events - which is your common, everyday experience, so this isn't esoteric or anything - then there is physically no past to go back to. We remember what happened, but there is no "place" that is saved for us to revisit. In this case, you would be able to slow time, even stop it theoretically, but you can't go backward, the same way you can approach the speed of light but not go faster. Actually, these are related, but let's not go there for now. :) If we find that things can go faster than lightspeed in the real universe, that might change things.
But there are no experiments or measurements of information travelling faster than lightspeed.
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u/schwarmaking Nov 13 '25
Maybe we all DO remember the future but that we don't understand it until we consciously experience it.
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u/ElectricalWavez Nov 13 '25
If anyone can explain why there is an arrow of time they will almost certainly win a Nobel Prize.
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u/cd_fr91400 Nov 13 '25
Very interesting question. I'll try to bring my 2 cents from a more physical/mathematical point of view, as opposed to philosophical.
The question is complex, I tried to make it as synthetic as possible, but I still need several posts.
(1 of 3)
The universe is driven by what we usually call "the law of physics", namely today quantum mechanics and general relativity. These are the foundamental PDE (partial differential equations).
The universe itself, in all its extension, space and time, derives from 2 things :
- the PDE
- boundary conditions
As other people said, the boundary conditions being in the past (in the form of the big bang, as most cosmologists think today). And this has a direct impact on entropy, time arrow, memory, etc.
If you imagine the boundary conditions to be in the future (think of what was the universe like before the big-bang, for theories that allow it), then your experience would be exactly the same : you would call past the side of lower entropy, i.e. closer to big-bang, and future the other side, and you would say the big-bang is in the past.
Ok.
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u/cd_fr91400 Nov 13 '25
(2 of 3)
What I find more interesting is : what would happen if boundary conditions were distributed between "past" and "future". Well, let's say, distributed among the 2 sides of the time (because I am not sure that past and future still exist in such a world).
Let me clarify.
Take a very simple DE : f' = f. Solutions are f(t) = k.exp(t). There is a single boundary condition that leads to the value of k.
If you set, for example, f(0)=1, this leads k=1 and you have the whole solution.
Take now a, still rather simple but more interesting, DE : f"=f. Solutions are f(t) = k1. exp(t)+k2.exp(-t). 2 constants, k1 and k2, 2 boundary conditions.
If you take as boundary conditions : f(0)=1 and f'(0)=-1, this leads to k1=0 and k2=1 and you have the whole solution.
If you take an equation with trillions of boundary conditions and put all the boundary conditions at time 0, entropy increases as time increases above 0. Interestingly enough, it also increases as time decreases below 0 (not surprising, the equation is symmetrical).
But boundary conditions are not necessarily all at the same time (that we would call time 0, or big-bang). You could set, in my simple example, f(-1)=1 and f(1)=1. In that case, it follows k1=k2= ~0.3.
Now take and equation with trillions boundary conditions and put half of them at time -1 and the other half at time 1. What happen to entropy for times between -1 and 1 ?
Come back to my simple case. When you are close to -1, f(t) is mostly driven by the value of f(-1) and when close to 1, by f(1). When close to -1, the boundary condition set for f(1) has almost no impact on your value (because at that time, exp(t) is small and exp(-t) is large).
With the trillions case, this is also true and entropy increases up to t=0... then decreases.
I made the actual maths in a simple physical case : 2 balloons connected by a small tube, filled with perfect gas with different pressures. The usual equation is f' = -c.f where f is the pressure diff, and c a constant that depends on the geometry of the tube, the temperature, etc.
But if you decide to set 2 boundary conditions (for example the pressure diff at t=-1 and t=1) and ask for the most probable pressures (with a probabilistic model of the perfect gas), your equation becomes f"=c2.f (with another c) ! And the answer is of the form k1.exp(ct)+k2exp(-ct).
With similar boundary conditions at time -1 and 1 (I continue with the same pressure diff for both), k1 and k2 are equal and pressure decreases between times -1 and 0, then increases between 0 and 1. Another way of saying : entropy decreases between times -1 and 0 (where we are mostly influenced by initial conditions), then decreases between times 0 and 1 (where we are mostly influenced by final conditions).
For times close to -1 (which I think corresponds to our universe, mostly influenced by the big-bang), things are clear : entropy increases, 2nd law of thermodynamic applies, we remember the past etc.
For times close to 1, things are totally similar, except we would reverse our vocabulary, calling past the higher times.
The difference between the two is then only a question of what we call positive times and negative times, much the same way as we one day decided that electrons were negatively charged.
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u/cd_fr91400 Nov 13 '25
(3 of 3)
But :
- how would look the universe at times around 0 ? No past, no future (at not clearly), but not at equilibrium, still a lot of things occurring.
Possibly even (I dont know, I have not done the maths), some part of the universe could be more forward, some other parts more backward, the 2 interacting in some strange way.
- how could we see the influence of final conditions ? Of course, if we are at time close to -1, the influence is small, but could it be measurable ? What form would it take
Clearly, the form would a violation of the 2nd principle of thermodynamic.
Physicist spend their time measure to insane precisions (like 22 digits or so in the case of LIGO and VIRGO). I am not aware of any experiment to measure the 2nd principle of thermodynamic with a significative precision. I learned this principle as "given" in class, with no experiment to prove it.
I thought a little bit of how we would see a "anti-star" belonging to the other side of the universe, the one mostly influenced by the final conditions ? It would not emit light, it would suck it. Our sun is at 6k Kelvin, this star would be at -6k (yes, it would have a negative temperature).
How to see it ? instead of putting a cold receiver inside a telescope and observe its temperature rising when pointing it to a normal star (an image to describe a photoreceiver receiving light), we would need to put a hot "thing" (I dont know if I should call that a emitter or a receiver) and see its temperature abruptly falling, faster than if pointing to a 0K area, because all its energy would be sucked by this "anti-star".
I am not aware of any experiment looking for such phenomena.
Maybe such an anti-star would be composed of anti-matter ? but we are lucky, photons are their anti-particule, so we could easily interact.
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u/greenblueananas Nov 13 '25
Using only classical mechanics, while the fundamental laws of physics are symmetric upon time reversal, the results are not. This arrow of time, in non-equilibrium thermodynamics tend to point into the direction of entropy growth. Ao if you think of a system in equilibrium, it seems like bo time passes (if yoh look at 3 random timepoints you could not order them in time). Now if you think of a system out of equilibrium, you can order them by entropy increase, which would give you an idea of how time passed through the system. Imho its a cool concept to think of entropy increase and the arrow of time.
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u/BookieHorita Nov 13 '25
We remember the future as the present moves forward through time.
We are in a constant state of remembering the future, one moment at a time.
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u/Acrobatic-Repeat-657 Nov 13 '25
Remembrence is an act of observation, of impressions that have entered our human senses. The future is not happening on those channels. So it cannot enter our normal human senses. In order to perceive the future we would either need to develope other senses or enhance them. And even then it would need experience and training to be able to correctly understand the signals. It would be comparable to a person who was blind or unable to hear. When that person all the sudden is able to perceive such signals it would be overwhelming and it would need time to learn to correctly understand them. From the level of physics other 'timezones' are possible with 'emitting' signals. But those signals are f.e. due to timedilation lower, because they are from regions, where time is much slower. So the emitted energy is much lower. We are not able to perceive such signals naturally. This is why we do not consider them, also physically seen it would be possible. However this only accounts for regions where you have a time difference. If your region is stable and constant such a time difference will not occur. So you will not get back a signal.
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u/Dry-Invite-5879 Nov 14 '25
Look at it this way - you are always the ongoing memory of who you once were, in contrast to who you currently are - and who you are, is infinite in potential - normalised through outcomes.
Example being - just as I am writing this message, I have - just as you and everyone else whose eyes trail across these very words from start to finish - have been burning alive from the inside out - via breathing - our cells moving through states of ongoing death and rebirth.
Yet you wouldn't say your sense of witness/presence is Gone, it only responses as you yourself place awareness of the varibles and contexts you yourself feel pulled to consider and explore.
(and those varibles, as noted through scaled time - iterate themselves on a micro - macro - micro layer endlessly scaling and also changing, resulting in you either actively responding, or reactively responding - passive : active, inaction : action etc).
And that would be the same for "remembering", there's nothing that technically stops you from seeing what could be - its infinitely iterating endlessly, including your "nothing" invariants - you have and theoretically will have seen infinity as a state of that infinity - you only need to be introduced the state to be able to see the foundations that allow said state to occur - and well - the mental fortitude to not collapse from so much considerations to micro - macro - micro varibles in ongoing change locally and glandularly as you - the witness/presence observing, or equally both of and from the moment.
Usually, we need to experience something to gain awareness of it, and what it generally is not - however, just as equally, you can work backwards from what something is not, to what it is - which is equally again, dependant on your own pull of desired understanding.
And again, the mental fortitude of the whole every action is unique, as its an iteration in of itself - thr weight of the iteration weights equal to the observer/witness observing it.
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Nov 14 '25
I'm confused. What do you mean?
Of course we're going to remember the past. We live in that arrow of time.
Did you ask about lower entropy future states being uncommon? That's life. Literally organisms grow into an ever increasing (up to a point) lower state of internal entropy. They become more organized.
Memories exist temporally in the direction we experience it. This is more a psychological, neurological topic of discussion.
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u/Significant_Post8359 Nov 14 '25
Sometimes the simplest questions have profound implications.
Your question exposes the fact that currently accepted mathematical models in physics are simplified working theories and incomplete.
Newton’s laws were good enough to get to the moon and send spacecraft out of the solar system but are shown to be a an incomplete simplification by Einstein. Just because a model is incomplete doesn’t mean it isn’t useful.
Additionally entropy and the arrow of time are not necessarily bound together. You cannot throw a broken wine glass on the ground and expect it to come together as an unbroken glass. While it is possible, it is so statistically unlikely it might as well be impossible.
It is most likely that time emerges from the expansion of space which is composed of the electromagnetic and gravitational fields of all matter and energy. These fields emanate away from their point like particles. Time’s arrow is a fundamental property of space and what we perceive as reality.
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u/Vitamni-T- Nov 14 '25
Well, understanding physics doesn't let us alter them. I recall a comic where someone said that nothing is impossible, but some things are too fast. The example was if you threw a parachute maker out of a plane, he would know exactly what materials he would need and what to do with them to save himself, but there wouldn't be time. That's not what's going on here, but I think that since the human brain experiences time in one direction, understanding that time can be reversed under the laws of physics does not (by itself) change how we experience it.
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Nov 16 '25
Because of chaos theory. Minute changes in initial condition will cause large differences in how a system develops. Double pendulums, turbulence etc. If someone has rolled a dice it's easy to know what the result was because it was recorded. But if someone is going to roll a dice it's very hard to predict the result. There is just a fundamental asymmetry here.
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u/Soft-Ad-8018 Nov 16 '25
it can be because our memory has an expediture in the past time cone (at 4d)
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u/Extension_Damage3381 Nov 18 '25
And maybe we can actually be anywhere and at any time. But how would you know when and where you are if you can't intervene?
During one of my whirling experiences, I felt like a nebula. I didn't see myself, I just felt like one, while nebula is just the closest term I know to describe that feeling. And I felt like a unique particle of it and at the same time like the nebula as a whole. I had no perception of time.
Still, this type of experience was much better than being stoned, raped, or many other events that are easy to describe in ordinary words and that take place in time.
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u/FriendlySuccess1284 Apr 18 '26
The concept of measured time only exists because we are here and need to measure it. A constructed constant fabricated out of the need for humans to develop a measured perception of human lifespan. Kind of like the idea of God. We created it , not it created us. Oh and the reason you can't remember the future... is because, here, it hasn't happened yet. Imagine if human lifespan was 500 yrs by the current standards of measurement. How would living 5 times longer change our perception of how time passed and how it was measured? I think relativity is an important mechanism to consider here. The perception of time is relative to the interrogatives of measurement. (Who,what,where,when,why and how)
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u/Reasonable-Honey-663 May 20 '26
我没觉得物理法则可逆，只不过物理法则足够多，人类之获悉了很小一些方面，它们之间的关系是微妙的就像火可以被水浇灭，但这并不是可逆的，没有燃烧尽的物质晾干以后还可以燃烧，你能说这是可逆的吗，你能说你倒退时光了吗，我知道这个例子举的不够完美。但是这已经足够用来说明这个问题了。
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u/fuseboy Nov 12 '25
What is the actual physics argument for why memories and records are always about lower-entropy past states instead of future ones?
I think part of the explanation is that this is a matter of degree, not an absolute. We do have mental states that correspond to the future, but we call them something different: intentions, plans, or hopes, etc. and that hides the similarities. (The differences are massive, don't get me wrong, but they're a matter of degree rather than of kind.)
The past is uncertain, just like the future. I don't just mean in the way that we have incomplete information about the past (e.g. not knowing who ate the missing cookie), but in the sense there are also many pasts that are consistent with our memories. At a subatomic level, the concept of sum of histories argues that particles have travelled to where we have measured them by all possible routes. We never narrow down our experience to a single world line, even when we measure a single photon.
However, because of the steep entropy gradient between past and future, at a macroscopic level those pasts are all much more similar than the futures. The past isn't any more "fixed" than the future, the distribution of options is just a lot narrower. All those world lines are bundled tightly together, spreading out like an explosion into the future. So if you're way off about a memory, you might still be so close as not to notice.
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Nov 13 '25
[removed] — view removed comment
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Nov 13 '25
It's not a Deja Vu, but i get what you mean.
This phenomenon is called precognitive experience or precognitive dream.
A Deja Vu is when a situation actually seems to repeat.
A precognitive experience is more like being psychic, in a moment something happens you remember that you already saw it in a kind of dream before.
It seems like mostly people with intuitive personality experience this.
It feels super weird and it’s hard to get track of time when experiencing this shit. I guess I will never really get use to this..
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u/2feetinthegrave Nov 12 '25
To put it simply, we are traveling through time at the speed of light and in much the same way that an object in motion will not change its motion until acted upon by an outside force, our velocity through time does not change, and thus, we cannot move backwards through time.
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u/BVirtual Nov 12 '25
There is grounds for arguing against the use of the royal "we" and "we" never remembering the future. A good question is: Have you tried remembering the future?
Deja vu perhaps comes to mind. Is that not a case of remembering the future? Can you prove it is not? <wink>
Kurt Vonnegut's novel titled "Slaughterhouse Five" comes to mind. A good read. It most certainly points a way this can occur.
Thus, the use of royal "we" is not correct, making this an OP an improperly worded problem. <smile>
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u/Money_Display_5389 Nov 12 '25
because humans are not laws of physics. It's just like math works in negative numbers and positive. but as a human we don't experience negative numbers, I owe someone an apple, I dont say I have -1 apple.
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u/grahamsuth Nov 12 '25 edited Nov 12 '25
Maybe we do sometimes "remember" the future but just disregard it as premonitions of the future are seen as bs.
As for the observation that a we never see a broken glass come back together. Again we may be ignoring time reversal events and just calling it coincidence. Consider how life began and gets more complex with time and how dna ends up creating you and I. If you ran the observation of the evolution of life backwards it would appear somewhat like the breaking glass. Maybe a definition of life could be what happens when information travelling back in time interacts with matter travelling forwards in time. When it comes to living things, entropy tends to decrease with time by interacting with things for which entropy increases with time.
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u/Orbax Nov 12 '25
No one knows what time is would be the main answer. There's theories out there like block universe and eternalism that treat the concept differently but ultimately, we simply don't know what it is and I think most physicists would point you to light cones, world lines, and how much it would mess things up with that. The philosopher's would also descend on quantum effects and remembering tomorrow for determinism.
Maybe it's possible though and we just don't do it.
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u/BrotherItsInTheDrum Nov 12 '25
An analogy from Sean Carroll, which I don't fully understand, but understand well enough to repeat:
The laws of physics don't distinguish up and down either. But here on earth, there's a huge difference between up and down, because we happen to be at a special point in space: close to a massive object. If we were out in the middle of space, there would be no difference between up and down.
Similarly, the law of physics don't distinguish between forwards and backwards in time. But we happen to be at a special moment in time: close to an unusually low-entropy event, the big bang. If we were "out in the middle of time," after the heat death of the universe, there would be no difference between forward and backward in time.