Unsolved problems in physics

http://en.wikipedia.org/wiki/Unsolved_problems_in_physics

by rms • 17 years ago

21 27 17 years ago

en.wikipedia.org

cool-RR10• 17 years ago

Physicists are ridiculous. Here's an unsolved problem for you:

Given the positions, velocities, masses and charges of a set of macroscopic bodies moving in vacuum, (in speeds which may be relativistic,) calculate the position of each of these bodies after a specified amount of time `t` has passed. (Neglect gravity.) (All quantities are given numerically, and the answers should be numeric too, allowing for a specified margin of error.)

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Until physicists can solve a problem like this, they can take their time with quantum gravity and string theory.

tome• 17 years ago

There's a big difference between having a verifiable theory for something which is computationally hard, and having no theory at all!

cool-RR10• 17 years ago

I'm sorry, I didn't understand what you are saying.

Are you saying that the problem I gave was computationally hard? I only want the algorithm, regardless of how computationally hard it is.

jlefo7p6• 17 years ago

I think you were referring to the n-body problem (http://en.wikipedia.org/wiki/N-body_problem). If so, I suggest not neglecting gravity.

Without gravity (and either assuming these guys don't run into each other or can somehow pass through each other), the position of each body is independent, and can be found through the following equation:

Position = Initial + (Velocity * Time)

Blah blah vector components blah blah, but you get my point.

ars2• 17 years ago

He included "charge" which (mathematically) is identical to gravity.

Plus he said relativistic, so the very concept of "position" (and time) is not so simple.

DarkShikari• 17 years ago

Mathematicians are ridiculous. Here's an unsolved problem for you:

Take a positive number n. If n is odd, triple it and add 1. If n is even, halve it. Repeat the process ad infinitum but stop if n reaches 1. For all numbers n, will this series converge to 1?

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Until mathematicians can solve a problem like this, they can take their time with the Riemann Hypothesis and Axiom of Choice.

;)

( http://en.wikipedia.org/wiki/Collatz_Conjecture )

cool-RR10• 17 years ago

Nice parody.

I think it's not a valid comparison though. Proving the Collatz Conjecture is not essential for understanding the Riemann Hypothesis, or any other such subject. It will probably not advance the proof of RH at all.

On the other hand, knowledge of the problem I raised, motion of charged macroscopic objects, is crucial to understanding Classical Electromagnetism, which is crucial to understand QM, which is crucial to understand most of modern physics.

schtog2• 17 years ago

I think we should close all hospitals. Those stupid doctors can't cure all diseases therefore medicine is complete useless.

cool-RR10• 17 years ago

I don't think your analogy is valid:

Knowing how to cure all diseases would be a very high goal that stands above what doctors accomplished up to the present time.

The challenge that I gave is below what physicists "know" today.

When a physicist studies Qunatum Mechanics, he knows that on the macroscopic scale, QM will behave like classical electromagnetism. The problem that I raise, is that physicists don't know classical electromagnetism well enough in the first place. They can't calculate motion of macroscopic objects. I don't think it's wise to try to study QM before they solved that challenge, the same way it won't be wise to start learning Special Relativity before you studied Newtonian Mechanics.

cool-RR10• 17 years ago

I apologize for saying physicists are ridiculous.

I hope that people who reply to post will state what they think is the status of the problem I raised. Do you think it's solved (give a solution)? Unsolved? Unimportant? Explain.

pfedor7• 17 years ago

So for starters, if by "macroscopic" you mean a object that has a finite size (as opposed to point objects), then the problem is underspecified, because you didn't give a model of the finite size objects' behavior under the action of external forces (the model typically used in classical mechanics is that of a rigid body, which means we assume a bunch of points which act on one another with forces necessary to keep the distances between points constant; but it cannot be used for relativistic systems.)

If we're talking about points, then the problem cannot be solved in classical electrodynamics because the classical electrodynamics doesn't address the issue of a charge interacting with its own field (for example, an accelerating charged particle emits radiation which slows it down, so called Bremsstrahlung; this phenomenon is not fully tractable withing the framework of classical electrodynamics; it is solved in quantum electrodynamics, to the extent that anything is.)

BobNeumann• 17 years ago

"Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics?[7]"

I die laughing at this one. "I know that my theory of the origin of the universe doesn't align with the laws of physics. SO THE LAWS OF PHYSICS MUST HAVE CHANGED SOMEWHERE ALONG THE WAY!"

ROFLLMAO

Maro• 17 years ago

What are you talking about?

Unsolved problems in physics

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