if everything obeys the law of physics, is it theoretically possible to predict the future accurately if we know all of such laws?


Edit: by predict the future, I mean predict every little event and it’s consequences in future, the human history and everything.

In: Physics

It depends on what do you consider predicting the future, while you can predict physical events that do not require humans, for example due to our understanding of physics we have a pretty good sense of when and how will the earth/the universe die, but due to the unpredictability of humans, it’s nearly impossible to predict the “future” if it has humans involved.

So basically yes, you can predict the future when it comes to physical and cosmic events, but as long as humans get involved it becomes too complicated with too many variables

Yes, it is possible. The problem is how far into the future you want to see. We can track things and predict their movement, such as planets, galaxies, comets, etc…

The two big factors that make it difficult/impossible are the human factors and not having exact numbers/data.

Think of a person playing billiards. His shots are calculated beforehand to get the ball in the pocket. The difficulty is controlling force, angle, etc… If we were able to reliably calculate/execute that with a robot, you could make the shots very easy to predict.

On a large scale, sure we can. We know when our sun is going to die, or when the next sunrise it. We also know (roughly) when the next mousson/rain seasons will start.

We cannot predict small scale stuff like whether you take peanut-butter/jelly on your sandwich tomorrow or if you’ll take a bowl of cereal.


But the problem is you need to know the initial conditions of all the atoms/ sub-atomic particles in the universe which the Heisenberg uncertainty principle forbids.

Not exactly. Our understanding of physics isn’t complete, but current science has established that subatomic particles don’t always behave deterministically. That is to say there are probabilities that a particle will do X or Y, and there’s no way to know which will happen until it happens. It’s a fundamental property of matter as far as we can tell with no way around it.

For everyday stuff on the scale of humans, it doesn’t make a difference. A person is made of billions and billions of these particles, so all that dice rolling going on at the small scale evens out and makes it look like everything is super predictable. Yet we still couldn’t perfectly predict the future because there’s just no way to track all those little dice rolls that could add up over long periods of time.

This is of course only speaking theoretically. The other problem is that if we wanted to do so practically, we would need to compute every property of every single thing in the universe. To do that you would require a computer made of at least as much stuff as exists in the universe. The only way to simulate something is to either use something bigger than the thing you simulate or to make some sort of approximations and simplifications, which introduces some error.

If you’ve ever played catch, you’ve predicted the future. People always think predicting the future is some grand feat, but we do it all the time.

Obviously, like covid, there’s somethings that are surprising. But you can still put together emergency kits and plans, because even if we don’t know exactly when we do know that bad things happen.

No, and this is a foundational principle of Chaos Theory.

In a non-linear dynamic system (even a system as simple as a [double pendulum](https://en.wikipedia.org/wiki/Double_pendulum)), even a tiny difference in the initial conditions will have a huge impact in how the system evolves over time, even if the system is fully deterministic. The [three-body problem](https://en.wikipedia.org/wiki/Three-body_problem) has been known about for a while.

An error in measurement will grow exponentially over time until the prediction is no better than if you had just put in the measurements at random (within the allowable values for the measurements). And because the error grows exponentially, how much your prediction improves doesn’t grow nearly as fast as how accurately you can measure the conditions. As the error goes to zero, how long the prediction is good for does not go to infinity, but to a finite value. And that’s before you throw in quantum mechanics, where the Heisenberg Uncertainty Principle puts a limit on how accurately you can measure something.

So if by predicting the future, you mean “predicting every little event and its consequences”, then no that’s not possible even in theory. And things like weather forecasts now take that into account. Rather than making one prediction, they make lots and lots of them with tiny little variations in each one and see how each plays out. The actual forecast is then more statistical in nature.

However, that doesn’t mean that predictions are entirely useless because some types of outcomes are more likely and some outcomes are impossible. With the three-body problem for example, if there are two large bodies and one small one, the most likely outcome is that the small body is ejected from the system.

No. Maybe you could predict anything that could ever happen in space (with the assumption that there is no intelligent life out there), but here on Earth a lot of events are shaped by human psychology and there aren’t all-encompassing laws or rules for that.

Also quantum mechanics and stuff. As far as I know (and I don’t know much at all, I’ve only dabbled), the laws of quantum physics have a certain element of randomness that can’t give you a definite/predictable outcome all the time.

The reason you are getting conflicting answers is that we don’t know for sure.

What you are talking about is called determinism, and scientists aren’t sure if the universe is deterministic or not. The physics of quantum mechanics relates to determinism, however the laws at this level are not yet well understood.

If the universe turns out to be deterministic, that will have a significant impact on physics, philosophy and our understanding of ourselves.

This is a very interesting question. Initially we thought no, events like a coin flip were random and impossible to predict.

Then Newton came up with classical mechanics, which explained everything about how objects move. If you knew the initial state and all the forces acting on a system, you could calculate how it evolved over time. This explained everything we could see universe, with enough calculations you could predict anything. It was gradually evolved over the next 200 years until it seemed like we had everything figured.

Then of course quantum mechanics came along, and with it came inexplicabally random events. Electrons that could be in many places at once and were impossible to measure properly, systems that seemed to be in a superposition of multiple states. Einstein hated the idea, arguing that “God does not play dice”. But quantum mechanics is still the best explanation we have.

So right now? We don’t really know. There are several possible interpratations of quantum mechanics, some of them suggest the universe is truly random, others suggest it’s deterministic.

Not everything does obey the laws of physics. Well, in the physical and biological senses, they all do. But that’s not the point.

You’re asking about predicting human history. That’s not subject to the laws of physics; it’s subject to human behavior.

And human behavior is definitely not subject to the laws of physics. What a person can physically do (eg.: running, but not flying) and biologically do (eg.: consuming food, but not photosynthesis) are.

But how a person will behave is not. There is nothing in the laws of physics that could lead to the conclusion of you asking this question in the first place, nor is there anything there about me answering it.

I’d recommend the TV show DEVS. It’s a one season mini-series. The central theme is heavily related to this.

Now if you take this question one step further and wish to keep yourself awake at night – does this mean we have free will?

Because either the universe is deterministic and we have no choice at all, or the universe is random and our choices comes down to pure randomness.

If this bothers you then West World has a good quote: “If you can’t tell, then it does not matter.”

Something I haven’t seen directly mentioned is radioactive decay.

Based on the current understanding of physics this is truly random. With a given sample of a radioactive isotope we know that half will decay within a given time period, but we do not know which half, and a good portion of quantum theory suggests that there’s no way to know which half.

Prior to decay two atomic nuclei are, at the limit of our understanding of physics, identical. There’s nothing to indicate that one has a shorter timer until decay than the other.

So you have all these atoms all through the universe that can spontaneously, and unpredictably, change into another (predictable) element, while simultaneously ejecting either aN alpha particle (a new helium nucleus) or a beta particle (an electron) along with some intensity of an electromagnetic wave. If it’s part of a molecule the chemistry of the molecule will radically change, and any atoms hit by the high energy helium nucleus or electron can also be changed too.

If those atoms were doing something important, for example were the DNA of a cell or they could be the tipping point of a cancer developing, or possibly be the factor in a DNA change that leads to a mutation in the species offspring going forward.

It’s not enough to know just the laws of physics, you need to know the exact position and movement of every individual physical piece of the system. This is actually impossible, due to the uncertainty principle attributed to Werner Heisenberg. The more you know about an object’s position, the less *you are able to* know about its motion, and vice versa.

Think of it this way: you can take a photograph of a ball in mid-air, and you’ll know exactly where it is in he picture; however, you know absolutely nothing about whether it’s moving, or in what direction. If the ball is moving fast (or you have an awful camera), the ball might look blurry or stretched out in one direction: this gives you more information about how it’s moving, but its exact position becomes a little less clear.

tl;dr no, because we can never have enough information to make perfectly accurate predictions.


In quantum physics there is a concept known as the Uncertainty Principle. Literally it says that you cannot know the precise speed and position of a particle at the same time. This happens because to know something, you have to measure it, and to measure it, you have to interact with it. Even if that interaction is as small as a single ray of light, it will still affect the particle, and you can’t know for sure what it does afterwards.

In the full sized world, you can think of it this way: Knowing the future changes the future. If you predict something, then now your own knowledge has changed, and that will affect your actions and choices.

So knowing the future requires not only knowing the future, but also knowing how knowing the future will change the future, and knowing how knowing the future will change the future will change the future, and…. so on.

Predictions could theoretically be very very precise (99.9% or more) but 100% perfect predictions are not possible. The very act of making the prediction changes what will happen.

In all likelihood the universe is deterministic (we don’t know for sure yet) in that all interactions follow predictable laws of physics, however it’s physically impossible to actually make those predictions so from our perspective we have to treat the the universe as if it is not deterministic.