# Can humans be scientificly expressed?

1. Jan 31, 2005

### eNathan

Can humans be scientifically expressed?

If you were given every peice of information about a person at any given point in spacetime, can you calculate what that person will do next? I know that we may never have the technology to do so, but do you at least think it is possible? If you know how much energy is every, the position of every atom, its velocity, and so on....

Either answer presents a paradox. If the answer is yes, you would have to agree that humans are an advance for of AI, if you answer no, that means you belive in something that we have not yet seen, much less prove.

I was going to ask this in the philosophy section, but I was afraid of getting a bunch of un-scientific answers, I want an answer from a strictly scientific perspective.

Last edited: Jan 31, 2005
2. Jan 31, 2005

### Gonzolo

This is the classical question of causality, determinism, and Einstein's "God does not play dice", vs Quantum mechanics, and perhaps chaos theory. There is no generally accepted answer. Roughly, every scientific person thought that "yes" until QM came along.

3. Jan 31, 2005

### Enos

I still think yes. Call me classical i guess.

4. Jan 31, 2005

### saltydog

No. When you say "spacetime", I assume you mean the whole Universe which I suspect has endless regression of cause and effect (or we encounter some singularity which changes the rules). If so, then we necessarily miss some connections. The statement "every piece of information" then becomes ill-poised (no offense). The missed connections show up in errors in the prediction. Einstein was wrong about the dice in my opinion.

Salty

5. Feb 1, 2005

### StatusX

Because of QM there is inherent randomness and uncertainty, so technically the answer is no. However, you could, in theory, scan every atom of a person and their environment (lock them in a room to make it easier if you want), then run a simulation on a computer. This simulation would have to have a random number generator to simulate the randomness of QM. Of course, the particular random path the real person and the simulation take would differ (although I don't know when these microscopic differences would manifest themselves into observable differences in behavior; maybe in seconds, maybe not in the person's lifetime), but there are two important points: a) Both would act human (and thus intelligent), and b) neither "person" would have control over which of the many possible paths they take; it is completely random.

Also, neither of the answers leads to paradoxes, just difficulties, and if you had knowledge of all of spacetime, the problem would be pretty trivial.

Last edited: Feb 1, 2005
6. Feb 1, 2005

### Crosson

"Because of QM there is inherent randomness and uncertainty, so technically the answer is no."

Quantum Mechanics does not imply inherent randomness, and in fact it does not even describe subatomic events. As Niels Bohr once said "there is no quantum world".

Quantum mechanics only makes predictions about observable consequences of subatomic events. The fact that observations are uncertain, even in principle, does not neccessarily imply a randomness, it may just reflect the fundamental nature of observations.

In the end, QM itself cannot determine whether or not the uncertainty in subatomic events is epistemological (having to do with the observers knowledge) or objectively real (fuzzy universe).

So QM says "it is impossible in principle to know the momentum and position of every (or any) particle in the human body". But the logical premise in the question is "if you did know the position and momentum..." and it is still possible to answer this question even though it refers to a non-factual hypothetical statement.

To summarize, QM does not imply randomness and I see know reason why it is incompatible with Causal Determinism. QM does however place limits on our ability to verify Causal Determinism, but this does not affect its truth value.

7. Feb 1, 2005

### Enos

god plays dice. But they are loaded and the outcome is predetermined. :P

8. Feb 2, 2005

### StatusX

Have you heard of Bell's theorem? It allows for a way to experimentaly distinguish these two choices, and so far, "fuzzy universe" seems to be the winner.

Of course, if local realism is wrong, as the experiments have suggested, particles don't have definite positions and momentums. In fact, they don't have anything until you measure them. As you said, the limit is on measurement, and since measurement is what gives particles their observables, the limit is on the actual observables as well. So in fact, it is logically, not just practically, impossible to know the positions and momentums of all particles.

Last edited: Feb 2, 2005
9. Feb 3, 2005

### loseyourname

Staff Emeritus
You just said they don't have determinate positions and momentums. If that if the case, you can know everything about the universe without the positions and momentums of every particle. Not possessing a piece of information that doesn't exist doesn't make your knowledge incomplete.

10. Feb 3, 2005

### Crosson

You guys are not philosophers, are you?

Just because it is impossible to know something does not imply it doesn't exist. This is the logical fallacy that has been embraced by the majority of mainstream physicists, which is why some have said that this era will be looked upon as a dark age of physics.

Going from the statement "it is impossible in principle to know the position and momentum of an electron with arbitrary precision" to the statement "electrons to not have an arbitrarily precise position and momentum" is an unfounded logical mistep.

Bohr, Shrodinger et al. knew that QM was a very powerful tool for predicting the outcome of experiments. They also knew that it had been patched together by trial and error, from a series of ad hoc assumptions. (which is fine, it works). Bohr once said "there is no quantum world", meaning that quantization, wavefunctions, bilocation, and probabilities are all convenient ways of eplaining observation, but do not neccessarily relate to whats actually going on down there.

Fast foward to the second half of the century, where it is common place to talk about a fantastic quantum world full of teleportations and randomness, because some people think it is interesting and exciting. In an actual QM class a kid asked "when an electron changes energy levels, does it move through the space in between?" and the professor, who appeared to be delighted, said "that's the spooky thing, according to QM it doesn't, and there is no arguing with an experiment". Yuck! QM does not make any claims about what goes on in that space, it only tells us that we will observe the electron in one of those energy states, and not any between.

StatusX, I am not totally disregarding what you said because it may have some truth to it. But untill you convince me that you actually understand Bell's Theorem, and can make your argument using Bell's theorem itself (and not something that someone has said about Bell's theorem), I will not be convinced.

To summarize, QM makes epistemic claims, about what we can know and observe, not ontological claims about what actually is. (except for the ironically ontological claim about what knowledge can be in a quantum universe). It is a big mistake to confuse these two because they are not equivalent.

11. Feb 4, 2005

### saltydog

I don't need Quantum Mechanics to explain this: Just look at man's never-ending attempt to find the smallest small. Give me a break. What makes Brian Greene and his gang think Strings are the end? I'm mean, I've witness two singularities in my short life time: protons to quarks, quarks to strings. My goodness, Ed Hubble, has it even been a 100 years yet? I don't think there is an end to cause and effect, only singularities which change the rules. Because of this we miss some of the connections thereby causing errors in our predictions.

Works for me.
Salty

12. Feb 4, 2005

### StatusX

First of all, position and momentum are terms defined by classical physics. There is no reason to assume these need to have definite values at all scales. That's like asking what color an electron is or the coefficient of friction of a proton. It may be that position and/or momentum really are fundamental, but there is no a priori reason this must be true.

The question of whether particles or their attributes exist independent of observation is more subtle. Bell's theorem says that if a particle really did have definite attributes (and if locality is true), it would yield different results in certain experiments than if it didn't. For example, two photons emitted by a single atom must have opposite polarizations to conserve spin. There are two possibilities: 1) these polarizations are determined from the instant they are sent out, and the fact that we can't get what they are until we meaure the photons just reflects a lack of knowledge. 2) the polarization isn't determined until we measure one of the particles, and at that instant the other particle assumes the opposite state, regardless of seperation in space. Now it can be shown that these two interpretations lead to different probabilities for certain measurements, and the experiments have so far shown the latter to be the way it is.

But this doesn't necessarily imply that things only exist when we look at them, because "measurement" hasn't been defined. It is possible that a measurement simply occurs when the state of a macroscopic system is correlated to the state of a microscopic system, and the huge ensemble of particles in the system in a superposition of states is unstable and the wavefunction collapses.