Slow down. Assuming that time moves in one direction is not comparable to geocentrism.
- There seems to be a special direction "down", where things fall by default, because we live in the vicinity of an influential object in space, called Earth
- There seems to be a special direction "forward in time", where things happen by default, because we live in the vicinity of an influential event in time, called Big Bang
If we had stuck to the local Earth context and geocentrism, the objectivity of the "down" direction would remain unquestioned. It's when we started modeling other things outside of Earth, it became clear there's no objective "down" direction, just a more general concept of Gravity.
Carroll's argument is that it's the Big Bang, an extremely low-entropy configuration of the universe, that gives rise to the 2nd Law of Thermodynamics and the resulting emergence of an arrow of time in the forward direction. It's purely a statistical phenomenon at larger scales, and attributable to being "next to an influential event", according to him.
Stars shine until they run out of fuel, and the age of a star - the status of its fuel, the buildup of fusion products - happens as time passes. Life on planets taps into the flow of sunlight from the star (and/or the flow of heat and chemical energy from the a hot planetary core) to generate complex structures in defiance of the regular direction of entropy (not violating conservation of energy, though). So... life reverses the arrow of time?
https://news.berkeley.edu/2016/09/20/new-book-links-flow-of-...
To butcher an insightful quote by (IIRC) Hamming, any positive slope will eventually make up for y-intercept of a constant function.
We cannot observe in any subset of possible universes where entropy is not present or is working backwards-Ergo those possibilities are wholly out of our direct perception.
That does not mean that causality cannot run in reverse, however, only that we cannot interact with those mechanisms in a way that would preclude our existence or observation.
Are photons themselves stratling this entropic boundary since they travel at the speed of light and within their own reference frame are not subject to the passage of time?
Sure, but some claims which cannot be tested experimentally or observationally are nonetheless important. For example, the claim “it’s important that scientific hypotheses be tested experimentally or observationally.”
Models created using both empirical experimentation and logical reasoning match reality much better than those based on "pure logics" (if that even is possible).
At least in France we take as fait accompli that causality is non trivial and that objects are non local at best: either you can consider objects as one despite immense distance between them, or you accept information passed between them in reverse time. Both are hard to swallow.
It doesn't defy the direction of entropy. Frankly, I'm not sure why you have that notion? Entropy is a measure of system's state of equilibrium. Moving energy from a concentrated source, and distributing it more equally (across life forms and other complex structures), is following the direction of entropy, as is it makes energy more equalized, in contrast to the former state where energy levels are more unequal between highly concentrated areas (like stars, the Big Bang), and areas with less energy.
The regular arrow of time from the human perspective, "leaks" changes into the future. The future is constantly being changed by the past.
You can measure those changes by many ways, the 2nd. law of thermodynamics is everywhere just to make sure you see this happening across everything.
So, probably there are other non-discovered underlying mechanisms in the reality that are already signaling changes from the future "leaking" into the past, changing the past right infront of us, without us noticing it.
A probably omnipresent mechanism for observing the future changing the past, valid in the whole cone of light visible to us, is the probability law.
If you have 10 millions of possible events in a probability, one of them is the exact thing it will happen in the future, hence the information of what happens in the future is right here, existing in the past.
Yeah, you can say how would the nature could use this information without powerful processors predicting branches trillions of times per second on Earth right now?
Well, the brain is a pattern predictor, quite several parts of the brain are firmly attached to the physics of the universe, biochemically but what if the pattern prediction mechanisms in the brain are actually an adaptation of the evolution, just like wings to fly, but with those mechanisms the brain uses probability to "see" information from the future, and here in the "present", it changes the past (from the perspective of the future created originally from the past), if the brain "chooses now" to do something different that what originally created the future it "saw" by analizing patterns, essentially evaluating probabilities.
So the Probability Law would be a kind of Inverted 2nd. Law of Thermodynamics.
It would work perfectly as law of the universe: from the future to the past, the revered time of arrow, one single event created "a" future, but from the regular arrow of time, there would a range of probable future outcomes which you cannot precisely say it has "1" (100%) probability of ocurring, right to exact moment till the future becomes the present.
And it was right there all the time, something obvious infront of everybody in the world, like electricity (which was suspected by many across thousands of years, but just "discovered" recently).
Roger Penrose proposed that as far as I know, when Carroll was probably a high schooler.
No. At least as early as Arthur Eddington when Penrose was a twinkle in his dad's eye.
This assigns credit to Carroll.
Perhaps given infinite time, we will randomly get back to a low entropy state infinite times, but I don't know enough about the math to say for sure.
It's basically a softer version of Russell's paradox but for cognition and reality.
Hard to summarize, but it's well worth anyone interested in this topic. There's a good bit where he ties the sleeping beauty thought experiment with Boltzmann Brains and consciousness; it blew my mind trying to understand the whole thing.
Just like noticing that "down" actually means "towards the center of the local planet" did not make water suddenly flow uphill.
Does that make more sense to you?
Have we observed reflected gravitational waves? In reverse-time, where would they originate from if they presumably rippled out into space and didn't collide with anything in forward-time?
Tenet has nothing to do with this- I'm just explaining it as it was covered in my many physics classes that covered the nature of the arrow of time (https://en.wikipedia.org/wiki/Arrow_of_time) and how I interpret it in terms of what seems most likely/least unlikely.
Let's consider something else - imagine an accretion disk of space dust slowly pulling itself together to form a planet. Play that in reverse, and you have the a planet slowly coming apart piece by piece. Imagine reversing the impact that created the moon. The moon comes apart piece by piece, creating an accretion disk around the earth, which then all moves and hits one area of the earth, and there several parts of it (and part of the earth itself) move together to form a separate planet, which then launches itself from the earths surface into space, flies around the sun a few times, and then slowly breaks apart piece by piece into another accretion disk.
F = ma
F = m dv/dt
u = -t dv/dt = -dv/du
- F = m dv/du
If you stop there it looks like you're right, but you also must change the definition of velocity to account for the new time.
v = dx/dt = -dx/du
+F = m dx/du
So the direction of gravity (the force F) stays the same when you flip time. I can explain that without the math by pointing out that if you took a video of a ball being thrown up and caught and played it in reverse, it would still depict a ball being thrown up and caught.
That's amazing, thanks. The portion where you caught the ball in forward time is equivalent to throwing the ball in reverse time.
I need to rewatch Tenet some day
> unbelievable (but still physically possible)
Physically possible - but in the same sense that the second law is not a physical law.
Another thought experiment that comes to mind is compressed gas in a cylinder. When we open the valve, the gas in the cylinder comes out. In reverse time, the gas would go back into the cannister and the valve would close after the gas went back in. Very low probability of that happening in forward time, though not not 0.
Though it seems weird, because why does the gas go into the cylinder? Because further into reverse-time, something sucked it all out (in forward-time, this machine is the compressor that put the gas in the cylider.) This hurts my brain!
Imagine a ball being thrown up and then falling down, in a parabola. Reversing a video of that still gives you a video of a ball in a normal parabola trajectory.
Well worth watching that episode as it does far better explaining than I do.
Also, geocentrism is actually disproven by numerous observations, which in fact guided the mathematical formulation of our current physics.
One thing is (almost) certain: the laws of physics as we know them (i.e. the Standard Model and General Relativity) are incomplete ("wrong"). That doesn't mean any old model is equivalent or as useful as either, though.
The validity of a coordinate system with the earth stationary at the center is guaranteed by the general principle of relativity. To get the stars to circle around it you would add a radially increasing potential in classical mechanics, or some coordinate shenanigans in GR. These coordinate systems are used in aerospace engineering to get convenient expressions of L1 points, etc.
I know it sounds hard to believe, but if you're willing to bite the bullet that "the center of the universe" has no physical meaning, then earth can't be not the center of the universe any more than it can be.
Certainly, there is merit in practical calculations when we are all this close to the ground where it all seems either flat or at least geo-centric.
But... the movements of the other planets in our solar system were really strange to model in geo-centric models. In short, each of the other planets should rotate around an imaginary axis to compensate for their changing positions in the sky.
Of course, all this is talk about in the context of our solar system. As for us being the center of the universe, well, the same argument holds for any other point in the universe. So, I think it's less likely than me winning the lottery in the next five minutes :)
It’s important to understand that astronomers chose it because it really seemed to provide a better explanation given the knowledge and technology at the time.
Tycho Brahe himself noted that his model could be disproved by observing the stellar parallax effect as the Earth orbits the Sun (if the Earth does move, then the stars would look slightly different throughout the year). This is a real effect, but so small that it couldn’t be observed until the XIX century.
I read an entire book on this subject, published by a Catholic press. There seems to be an active interest in the Catholic science establishment in rehabilitating some of Galileo’s critics.
I disagree.
The sentence «"the center of the universe" has no physical meaning» requires that Earth can't be at the center of the universe, because there isn't a center for it to be at.
You're still allowed any or many arbitrary zero-points, but that's only the center of a number line, nothing else.
But, Earth.x = 42 (in some arbitrary coordinate space), if I understand correctly there isn't a sub-light coordinate space in this universe where Earth.x = undefined.
By analogy, while spherical coordinates are arbitrary, latitude is defined. Arbitrary, but defined.
But the centre of the Earth has an undefined latitude, and a topological subspace consisting of just the surface of the Earth can't hand-wave past that by pointing out that's just a coordinate singularity that can be safely ignored — there isn't a center of the Earth anywhere in that subspace. If the universe is flat and finite (looping), this problem still exists.
And if the universe is unbounded (infinite), that has a different problem because you can't properly define a median of an infinite set[0], so no center exists.
If it just stops suddenly after a certain amount of space, then we get to have a center, but there's no sign of that.
[0] I think. Infinity is easy to get messed up with.
Be patient. It hasn't been evaluated just yet.
Or if I’m lucky enough to have the time to watch the moon move slowly, it feels natural to my senses to say it’s moving across the sky. The moon feels like it’s moving around me. But I can stretch my brain and imagine the reality.
Sometimes math arrives first. We have the new maths (or an problem in current math), and that points to some possibility. Because it’s not observable, ignoring our senses is a requirement to develop that in the model and measurements and experiments. Eventually we are able to observe it.
I’m not familiar with history of astronomy. Would it be the case where the observations that lead to heliocentric thought we nuanced and had to build on more obvious perceptions that things aren’t adding up? Was the wobble of Venus part of that?
And you’re right, old models are useful and remain relevant a lot! The model of time moving linearly will likely always be the most useful model for navigating our daily choices (if we have any at all!)
Why not?
The "arrow of time" almost always requires thermodynamic arguments. And that requires a concentration of "low entropy" to move toward "high entropy". Which, by definition, are "boundary conditions" and not a fundamental part of your physical rules.
If, for example, your universe is entropically uniform, is there an "arrow of time"? And, even if there were, could you detect it?
However, I would like to point out that it's not like we haven't had this kind of issue before. The Bohr-Einstein debates were a good example. Einstein favored a "fields" interpretation of quantum mechanics. Unfortunately, Einstein's interpretation predicted that atomic states wouldn't decay, and that was clearly, obviously wrong, and Bohr very much hammered on that.
Except that Einstein wasn't "clearly, obviously wrong." As you increasingly isolate excited atoms, their atomic states take longer and longer to decay. The problem was that the experiments of the day couldn't create these kinds of singular quantum state systems--they were stuck with systems that were contaminated with lots of thermodynamic interactions.
We may be seeing something similar here. We are just starting to be able to put together the experiments that can probe things like Bell's Inequality. As we isolate these systems, we may find that the systems were contaminated with statistical time and that we get different results when we can isolate them.
What does that even mean? If your universe is entropically uniform there is no “you”.
Nope, and there's a really great 'physics slam' about this, sadly only in German but auto-translate seems fine. https://youtu.be/z64PJwXy--8?t=519
Would we have fluctuations in that state? In which directions they would... Progress?
Isn't what you describe an anomaly like black hole or division by zero, where we cannot understand what actually happens because normal laws break because they are unsolvable with current models?
Your entire experience of the world is defined and limited by the fact that your brain "only processes information in one direction of time" (for lack of better wording). Your personal experience does not necessarily map correctly to the real world. The same is true for both examples.
Our brains like to process events in a linear sequence, from past to present to future, but this view of time might not fully capture how everything in the universe is interconnected. It's possible that our language just can't handle these complex concepts.
So, I don't think anything mentioned in this thread contradicts the idea that "time always moves in one direction" and "entropy always increases".
So no, it's not at all incompatible with retro-causality. When you think about retro-causality, the idea that time "moves" is completely superfluous. Time is probably not even a real thing.
More on topic, I think our existing theories of reality tell us that the future probably affects the past, or at very least, is predetermined. If you know the solution to a differential equation, you know the state at any point in time. There's no going off the rails, so to speak. And if the system is constrained in any dimension (i.e. it's nonholonomic) then the state at any given moment relies on the full trajectory up to that point, as opposed to just the previous state. But you can flip that on its head and say that the future state determines the present trajectory. E.g. to turn a bicycle left, you have to first turn right.
I'll expand here how if the arrow of time actually doesn't exist, the future could change the past without breaking our - current - understanding of physics (tragiclly because we will probably have maybe hundred of years till we change our minds about what are the properties of the universe).
In a range or probabilities of one event, one of the probabilities will always be the one is going to actually happen. Closer to the event to occur the most certain you can be about which one of those, could be the one that will happen.
Here's the catch, you have to change your mind a bit, in our current understanding of physics, the information of the future event which has not happen yet, already exists here in the past for that event.
Now, if you know - and you know - the outcome of an event, you most certainly will be able to choose if you go along that path, or you choose to change the future event to something else. Whoalá, the future changed the past.
Brains of earth continously do this, every second of our entire lives, animal brains do this too, almost all life on Earth has some neurological, physiological, chemical predictive mechanism in place.
An example, you're about to walk across a street, you see a car coming, now your brain "predicts" you'll be hit by that car if you just keep walking, you stop walking to avoid certain death, done, the future changed the past. The information - really close to 100% of probability of death - extracted by the brain from the sheer reality of the universe, allowed you to survive.
And no current understanding of physics got harmed anywhere along the way of the future changing the past.
Granted, I'm not a physicist and I'm sure any physicist working on this totally understands that. Just wanted to point it out.
The biological processes enabling that sequence can be said to have negative entropy.
(It's like a rollback of database transaction, where not only the database state, but also the state of everything, including your brain, is getting rolled back)
Though there's no hard evidence, but if you think, for example, about the efficiency of evolution - it would be much easier to explain if we assume that the unlimited number of iterations is performed. (This is not the only possible explanation, of course- but this one is overlooked IMO)
I would say that compared with the strange ideas like "multiverse", this one is rather benign :-)
Scrambled eggs do actually unscramble spontaneously if you zoom in far enough. The issue is that the rate of scrambling is much higher than the rate of unscrambling so on the whole, you get scrambled eggs.
The amazing thing is that all chemical processes are actually reversible given enough energy and finesse.
If time is a true dimension rather than just something we model as a dimension, it's not unreasonable to think that outcomes in the present could be influenced by constraints that exist in the future - if the "universe" function must be valid according to some constraints at all points in the time dimension, "past" states that lead to invalid future states will never occur.
The idea of invalid universe states is of course purely fun conjecture, but this same concept also maps to probable vs improbable universe states as well. If a future state is improbable (in the sense of a Bayesian prior according to some underlying distribution of energy in the universe) that might cause the universe to evolve in a way that seems improbable at the moment by moment level, but is actually the most probable sequence of events when integrated over the entire duration of the universe.
(On a personal note, I'm actually sympathetic to the article's retrocasual proposition. I suspect reality is non-local and TSVF etc. naturally tend towards non-locality.)
* This is Vice, of course they use the popular understanding and not something more sophisticated.
I commented further in this line of though in another comments, about a probable (ironically), "Inverted 2nd. Law of Thermodynamics" of sorts, which it would be basically just the Law of Probability, interpreted from the point of view of not having an actual arrow of time and the fact that we have - all the time, again ironically - the information of what happens in the future (the one probability in the range which ends being the right one, actually ocurring).
Yeah, I know it would be another Law, and the universe would upside down once again for us the poor meatbags, but we were already in this position several times, discovering the electricity, quantum mechanics, relativiy, you name it.
The idea doesn't seem so different from matter being the default (vs. antimatter), relative speeds much closer to zero than to the speed of light being what's commonly observable etc.
Nature doesn't have to obey any particular set of axiom you adopt.