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A growing number of scientists are convinced the future influences the past

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Re: A growing number of scientists are convinced the future influences the past

#191

Post by dekhn »

Nevermark wrote: post #72
wootland wrote: post #15

As a non-physicist I'm not sure I'm interpreting this correctly. Does this essentially mean that all states in time already exist and our consciousness is just traversing this 4D space in one direction on the time axis? If so, does that mean that the big bang could actually be the end of the universe and we're just experiencing time in "reverse" toward an initial starting state that we perceive as the future?

While most laws of physics may be time symmetric, the laws of thermodynamics are not - wherever there is a gradient in entropy. In very informal terms, anywhere where there is very low entropy (higher order), any direction away from that will likely (to the point of certainty) be in a direction of higher entropy (lower order). For instance, if you have a jar of red & blue marble, with high order (such as perfect alte…

Not sure if you appreciate this, but if you repeat the shaking experiment enough times, you will see it return to perfect order- at some exceptionally tiny probability. I'm pretty sure you are saying that but instead of "practical amount", it's easier to say it's just exceptionally unlikely.

Re: A growing number of scientists are convinced the future influences the past

#192

Post by sdwr »

TechBro8615 wrote: post #147
sdwr wrote: post #66

Earlier quoted context omitted.

Was coming to say something like this. Gets to some fun conclusions - ex. paleontologists invent dinosaurs by looking for them. Another angle on it would be showing that the universe has multiple possible levels of detail - that objects behave like newtonian point masses most of the time, that digestion is replaced by a simple hunger meter when nobody's paying attention. From this direction, time's main function is c…

This thought experiment implies that humans, or conscious agents, represent a highly concentrated source of entropy, currently (mostly) confined to planet Earth. Meanwhile, in the vastness of space, most of the mass has settled into some relatively deterministic equilibria, with no conscious agents to alter the course of its future. Yet we're down here on the blue planet messing everything up. Coupling this thought w…

My guess is it would conserve entropy/processing on Earth to match the increased cost.

But there's a difference between "screaming into the void", like broadcasting radio waves, that presumably have 0 effects, and other things.

Re: A growing number of scientists are convinced the future influences the past

#193

Post by TechBro8615 »

a257 wrote: post #173
TechBro8615 wrote: post #166

Earlier quoted context omitted.

We're talking about physics, not mathematics. We don't have the luxury of hand-waving away fundamental questions about the nature of the continuum. See: https://en.wikipedia.org/wiki/Continuum_hypothesis

Please elaborate.

I'm neither a mathematician nor a physicist, so I'm not nearly informed enough to elaborate on the subject properly, but I would note that the axiom of choice is not proven, and while you can mathematically divide a continuum into infinitesimally small sets, you cannot do the same to physical matter. From my understanding, many of the contradictions between classical and quantum physics arise at this boundary between the discrete and the continuous, where classical physics generally assumes continuity while quantum physics is constructed around discrete quantization mostly independent of time.

Again, I'm not a physicist, but I think it's telling that the validity of continuum mechanics [0] depends on a model and multiple assumptions. I have no trouble agreeing with your original statement, "with enough marbles, the discrete distribution behaves like a continuous distribution," when speaking mathematically, but mathematics by its nature is an idealized model of the world - I'm not willing to accept that it's objectively representative of physical reality. The discussion we're having here is one of metaphysics, so it feels a bit like the height of hubris to use mathematics as the tool for describing objective reality, because metaphysically, we cannot say that mathematics is anything other than a tool we've constructed for approximating the model of the world as we understand it. Considering the subject of this post is about retrocausality, we're already throwing out some pretty wild ideas, so I think it's a bit hubristic to dismiss them by citing a branch of mathematics that assumes the existence of countably infinite sets [1].

[0] https://en.wikipedia.org/wiki/Continuum_mechanics#Validity

[1] https://en.wikipedia.org/wiki/Constructivism_(philosophy_of_...

Re: A growing number of scientists are convinced the future influences the past

#196

Post by prerok »

whatshisface wrote: post #114
sidlls wrote: post #108

Earlier quoted context omitted.

It isn't because we have the observations we have. It might be mathematically easy to invert time, but empirically it's not so simple. Mathematical symmetries and expressions are nice, but then the actual physical consequences and requirements (e.g., material, time, energy inputs) sort of force one's hand. Also, geocentrism is actually disproven by numerous observations, which in fact guided the mathematical formulat…

> Also, geocentrism is actually disproven by numerous observations, which in fact guided the mathematical formulation of our current physics. 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. The…

To be honest, I have no idea what you are talking about.

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 :)

Re: A growing number of scientists are convinced the future influences the past

#197

Post by dekhn »

soperj wrote: post #90
Nevermark wrote: post #72

Earlier quoted context omitted.

While most laws of physics may be time symmetric, the laws of thermodynamics are not - wherever there is a gradient in entropy. In very informal terms, anywhere where there is very low entropy (higher order), any direction away from that will likely (to the point of certainty) be in a direction of higher entropy (lower order). For instance, if you have a jar of red & blue marble, with high order (such as perfect alte…

> And no practical amount of shaking the jar will ever return the marbles to a high order state again. This can't be true. Take the case where there's only 2 marbles, it's likely that at some point that shaking them will return them to the original state. For higher numbers of marbles the probability becomes lower and lower, but is never 0.

you're correct. In stats/thermo class there's a commonly taught "what's the probability of all the molecules of air in a room spontaneously moving to ". The problem is that shoving all those molecules into a tiny location woudl increase the pressure tremendously, sending all the particles in directions that would eventually return to a uniform distribution.

IIUC my professor right the probability is non zero but is practically impossible for a large number of incompressible spheres.

Re: A growing number of scientists are convinced the future influences the past

#198

Post by dekhn »

a257 wrote: post #168
PartiallyTyped wrote: post #162

Earlier quoted context omitted.

Any point is infinitely improbable when sampling with infinite precision, only because this calculation is not computable. Even if the point probability is 0 or approaching zero very fast, some event occurs with probability 1. The probability that life would evolve on a blue planet that its anthropomorphic inhabitants will come to call Gaia or Earth, has as a star Sol, in this corner of the Milky Way, in this particu…

A probability of zero does not mean that the event is impossible. When we refer to probabilities we are talking about probability densities. Infinite precision is a useful modeling tool in the same way that approximations of pi are useful.

In a well defined system, a probabiltiy of zero by definition means an event is impossible.

Re: A growing number of scientists are convinced the future influences the past

#199

Post by platz »

psychphysic wrote: post #181
0xBABAD00C wrote: post #134

Earlier quoted context omitted.

Here's the analogy, per Sean Carroll [1]: - 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 g…

I don't think Carroll can take credit for the idea of the arrow of time being emergent from a local entropy initial state. Roger Penrose proposed that as far as I know, when Carroll was probably a high schooler.

who's taking "credit"

Re: A growing number of scientists are convinced the future influences the past

#200

Post by stkdump »

If time were symmetric, wouldn't that mean instead of causality (future is influenced by the past) and retrocausality (past is influenced by the future), there is no preference and in effect no causality at all? A&B are necessarily connected, but none of them is the cause of the other.
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