Science's Big Query: What Can We Know, and What Can't We?

The Wall Street Journal ^ | Friday, May 30, 2003 | SHARON BEGLEY

[tictoc]

No matter how infinitesimal the moment of being in a position, for that moment there is no movement, ergo, no momentum.

Interesting thought... Some scientists believe that time is discontinuous at the shortest scale (I believe it's called "Planck time"). So like a gigantic clockwork, everything in the universe moves a step, stops, moves a step, stops...

[Mind-numbed Robot]

Yes, but that again is an entirely different proposition and relates to relativity when we were discussing objective observations from the same perspective. You are correct if you divorce my comment from its frame of reference and examine it literally and without context.

[Mind-numbed Robot]

Not having a technical background I had not heard of that theory. It is an interesting thought, I agree, yet when considered within this discussion it seems entirely reasonable.

[tictoc]

Here's a link for you: http://www.nature.com/nsu/020304/020304-5.html

[ConservativeLawyer]

Bump for later reading.

[MOX]

Fitting moniker.
Ever heard the expression "It is better to remain silent and be thought and idiot than to speak and remove all doubt"?

[Alamo-Girl]

Great poem, Physicist! Kudos!

For the record, I don't think such a thing is possible, but for a long time after my dream I could not shake the notion of "fossil sound" out of my head!

For the record, I do think such a thing is possible because I see no reason sounds could not be captured into the resonance super-strings, i.e. string theory of particles as resonance.

[Mind-numbed Robot]

Thanks for the link and the article fits right into this discussion. I was not previously aware of the derivation of the word quantum as used here:

They are named after the German physicist Max Planck who initiated quantum theory, which posited that the energies of atoms and molecules are quantized, or discretely divided.

[Mind-numbed Robot]

Fitting moniker. Ever heard the expression "It is better to remain silent and be thought and idiot than to speak and remove all doubt"?

Where did that come from? Care to give me a hint?

By the way the original expression said "fool", not idiot.

[longshadow]

Yes, but when you introduce momentum, or movement, you can't have just one place. You need a sequence of places and therefore no ONE place. As a result, it seems to me, the concept of momentum and position simultaneously is mutually exclusive.

Calculus addresses the very issue you are raising. Thanks to Leibnitz and Newton, we are able to meaningfully talk about things like instantaneous velocity, momentum, and position.

Also, your earlier comment about a non-moving object not having momentum is technically incorrect. It DOES have momentum; it just happens to be zero. Heisenberg is saying that we cannot similtaneously know BOTH the position and momentum of quantum particles to an arbitrary degree of accuracy, even when the object is standing still. It is precisely this constraint that tells us that the electron in a Hydrogen atom cannot continue to shed energy after it is in it's ground state, and spiral into the nucleus. If it could, we'd know both the position of the electron (in the nucleus) and it's momentum (zero) at the same time. In effect, Heisenberg's Principle defines the lowest energy state of the electron in an atom; to go any lower would violate the principle.

[!1776!]

Interesting thought... Some scientists believe that time is discontinuous at the shortest scale (I believe it's called "Planck time"). So like a gigantic clockwork, everything in the universe moves a step, stops, moves a step, stops...

There does seem to be a lot of "discrete energy packets" in modern physics, maybe someone will apply similar principles to time and make a step forward...

You can never see the leaps and bounds coming in science, it justs happens, usually from a lot of hard work, coupled with the investigation of thousands of dead ends, and complimented with a unique way of looking at the question at hand.

Can't know position and momentum at the same time? Maybe the idea of looking at them as stand alone quantities is a hard to shake concept that while fitting for everyday use, is just to simplistic for detailed reality.

[tet68]

Without another world to show us different laws of nature, "I think we can never know for sure if the universe had to be the way it is, or if other laws of physics would allow other kinds of universes," says Prof. Hut.

How do you ever know?
How do you ever really know?
Sigh.


This mantra brought to you by the Church of the Future. tm.

[Mind-numbed Robot]

Thanks for the explanation. I can see that my attempts at real world logic and quantum world observations and descriptions are not going to be compatible.

It DOES have momentum; it just happens to be zero.

Wouldn't that be potential momentum? I know, I know, definitions. Since you have been so kind perhaps you will explain to be the difference between momentum and inertia. In the real world I thought they were opposites but I have seen inertia used in ways that I would have used momentum.

[VOA]

Science's Big Query: What Can We Know, and What Can't We?

Wasn't this ground covered by philosopher David Hume some centuries ago...

[error99]

"...What if stalactites could talk? If these icicle-shaped mineral deposits somehow preserved the sound waves that impinged on them as they grew, drop by drop, from the ceilings of caves..."
- - -
Yes, but all we would hear would be that incessant:
drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip...

[boris]

"Why do scientists earn a PhD, Doctor of Philosophy? One would think there is some philosophy involved along the way."

At M.I.T. they give an "ScD". I got an "SM" which I joke stands for Sado Masochism. And yes, the undergrads get SBs.

--Boris

[boris]

"Perhaps my ignorance and mental limitations blind me to the obvious but the answer to this problem seems to be in the semantics. For a particle to have a position it must be fixed in space, not moving. If it is fixed it has no momentum. Therefore, momentum and position are mutually exclusive."

You can apply it to energy and position as well. It is fundamental, and not semantical at all.

--Boris

[boris]

A fundamental question left unposed is: "what is time"?

Some wag said "time is what a clock measures," as if this were an answer.

The more I read about time the more confused I become. Rudy Rucker (the mathematician and SF writer) once asked Kurt Godel: "What causes the illusion of the passage of time?" Godel answered obliquely but did not complain the question was nonsense.

Recently I read Julian Barbour's The End of Time (twice), becoming more confused the second time.

I think there is a deep mystery here; something we are simply not constructed to understand (being creatures embedded in time).

Does a fish know it's wet?

--Boris

[longshadow]

Since you have been so kind perhaps you will explain to be the difference between momentum and inertia. In the real world I thought they were opposites but I have seen inertia used in ways that I would have used momentum.

Inertia: 1 a : a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force.

The property of a parked railroad car that "resists" moving when you push on it is an example of what we mean by "inertia." The inertia of the railroad car makes it harder for you to change it from sitting still to moving than it is for you to accelerate a ping-pong ball.

Inertia is a property or "characteristic" we associate with matter (things that have "mass.")

Momentum is a physical quantity associated with matter. Specifically:

p:=mv
where "p" denotes momentum (in this case, linear momentum, meaning that it applies to things that aren't in rotational motion; there is a form of momentum associated with objects moving in rotation, called "angular momentum"), "m" denotes the mass of the object, and "v" denotes the objects velocity as measured in some frame of reference. Velocity is a "vector" quantity (it describes the object's direction AND magnitude of motion) while mass is simply denoted by a magnitude, so it is what is known as a "scalar" quantity. The product of a scalar quantity and a vector is another vector quantity; thus, momentum "p" is a vector quantity (it has both direction and magnitude) and both momentum and velocity are depicted in bold type in many texts to signify their status as vector quantities. So, in conclusion, the "momentium of an object is simply the product of its velocity and mass.

The confusion of momentum and inertia comes from the fact that both are intimately related to the mass of the object. But while inertia is a general property of matter, momentum is what we can measure or calculate for specific objects.

(there is another concept in physics called "moment of inertia", but that's a lesson for another day....)

Hope that helps..... there'll be a quiz next period!

[longshadow]

A fundamental question left unposed is: "what is time"?

"Time is the because with which some dolls are stuffed." - e.e. cummings