Why is light travelling in "straight" line? (see restrictions)

**fhisicsstudnt** · Nov4-09, 02:51 PM

Originally Posted by haushofer

Can you give an example of a theory in which concepts are explained in terms of "what they are" instead of "how it behaves"?

Concepts are inherently a description. Objects "are what they are". A theory of "what it is" has to present an object (particle, fluid, string, etc.) first before it can describe the behaviors.

In older times, everything was explained in terms of discrete corpuscles. Atoms and light were all particles (what they are). But it couldn't explain diffraction, then the aether wave hypothesis couldn't explain the MM null result or quantization. I don't know of any more qualitatively different "what it is" hypotheses.

**haushofer** · Nov5-09, 03:48 AM

Originally Posted by fhisicsstudnt

Concepts are inherently a description. Objects "are what they are". A theory of "what it is" has to present an object (particle, fluid, string, etc.) first before it can describe the behaviors.

In older times, everything was explained in terms of discrete corpuscles. Atoms and light were all particles (what they are). But it couldn't explain diffraction, then the aether wave hypothesis couldn't explain the MM null result or quantization. I don't know of any more qualitatively different "what it is" hypotheses.

Well, I don't really see the big difference between the description of light in QED and the description of other physical concepts in other physical theories :)

**fhisicsstudnt** · Nov5-09, 10:59 AM

Originally Posted by haushofer

Well, I don't really see the big difference between the description of light in QED and the description of other physical concepts in other physical theories :)

You don't see the difference between that which you can visualize and make a movie of to explain a phenomenon, vs. a set of equations that gives you the result of an experiment?

**DaleSpam** · Nov5-09, 05:10 PM

Originally Posted by fhisicsstudnt

A description/characterization is not unique, it doesn't guarantee understanding. I can describe the ball's motion as 9.8 without understanding. I can describe all the motions of the planets without any understanding. In fact, I can do so with a completely wrong understanding.

So yes, a description can be a very useful thing. It can also be a complete dead end. The question, then, is whether Nature is "understandable" to humans or are we relegated to simply identifying and correlating patterns in the data.

This goes back to my previous question: if you can predict every single aspect of something's behavior and characterize its every property and all interactions and still not "understand" it then of what possible value would be "understanding" it?

However, it appears to be a purely semantic argument. From your previous responses it seems like you and I both agree on the fact that QED accurately predicts and describes all observed EM behavior. We only disagree if that qualifies as "understanding" what light "is" or not. Personally I find semantic arguments rather boring so I am not inclined to pursue the "understanding" disagreement further.

Originally Posted by fhisicsstudnt

The original poster didn't ask about data or for a description. S/He asked "why" light travels straight.

Good point. "Why" questions are often rather non-scientific. A more scientific line of questioning would have been:
Q: What underlying principle results in light traveling in a straight line?
A: Conservation of momentum.
Q: How is momentum conserved in light?
A: Due to the space-translation symmetry of the electromagnetic Lagrangian.
Q: What makes the electromagnetic Lagrangian symmetric?
A: Symmetries are neat, they help you "understand"

! Stop asking so many questions.

Originally Posted by fhisicsstudnt

Objectively we can ask why X moves Y. We have to define X and Y to answer the question. If X is an equation or a set of data the question is meaningless.

I disagree here again. I think the equations of a theory are much more important than the interpretations.

Originally Posted by fhisicsstudnt

You don't see the difference between that which you can visualize and make a movie of to explain a phenomenon, vs. a set of equations that gives you the result of an experiment?

I don't see the difference. I can easily visualize an equation or make a movie of it.

**fhisicsstudnt** · Nov7-09, 08:48 AM

Originally Posted by DaleSpam

This goes back to my previous question: if you can predict every single aspect of something's behavior and characterize its every property and all interactions and still not "understand" it then of what possible value would be "understanding" it?

But no mathematical formalism does. It may match to the 10th, 14th, 20th, etc. decimal place. Where one draws the line is subjective. 14 seems incredible right now, but the Borg are laughing at us, their instruments measure to 50 decimals and they can tell we're WAY off from the 15th decimal on. We're not even close to right! Another civilization rolls their eyes, they've characterized matter all the way down to the 1000th decimal place. The humans and Borg are both way, way off. Meanwhile God (Nature itself) "measures" an "infinite number" of decimal places.

We start out with a mathematical formalism that is somehow qualitatively/conceptually flawed, but

Originally Posted by DaleSpam

I can easily visualize an equation or make a movie of it.

But the equation is not the thing acting. By visualization I mean visualizing the invisible actors in the play and how they behave to produce the observed phenomenon.

**DrGreg** · Nov7-09, 09:27 AM

Originally Posted by fhisicsstudnt

But no mathematical formalism does. It may match to the 10th, 14th, 20th, etc. decimal place. Where one draws the line is subjective. 14 seems incredible right now, but the Borg are laughing at us, their instruments measure to 50 decimals and they can tell we're WAY off from the 15th decimal on. We're not even close to right! Another civilization rolls their eyes, they've characterized matter all the way down to the 1000th decimal place. The humans and Borg are both way, way off. Meanwhile God (Nature itself) "measures" an "infinite number" of decimal places.

I'm puzzled how you think an equation might be accurate to only 10 decimal places but a "visualisation" might be accurate to 20 decimal places.

It's quite possible that some of today's theories might one day be replaced by even better theories. But the new theories will be described through equations.

**fhisicsstudnt** · Nov7-09, 09:54 AM

Originally Posted by DrGreg

I'm puzzled how you think an equation might be accurate to only 10 decimal places but a "visualisation" might be accurate to 20 decimal places.

It's quite possible that some of today's theories might one day be replaced by even better theories. But the new theories will be described through equations.

A visualization does not have decimal places. It's qualitative, not quantitative. An example may help communicate what's in my mind.

I measured the velocity of A to be 5 and B to be 4 ; quantitative
A moved faster than B, A hit the wall before B; qualitative

The 2nd statement doesn't care if we know velocity to 1 decimal point or a million. It is either the truth or a lie, depending on if A actually hit the wall before B. We can visualize one object arriving at a destination (wall) before another one. We can scale our visualization to whatever scale necessary to appreciate the difference in arrivals, i.e. I can decide that each frame of my movie is a msec, mcs, ns, fs, attosec, etc. The magnitude scale is irrelevant. My visualization doesn't care how big or tiny the quantitative difference is between A's velocity and B's, it only cares about qualitative stuff, A got there before B.

Quantities are inherently different in that they cannot be "Right" because we can't measure infinite decimal places. Nature doesn't know about decimal places or accuracy, it has an "infinite number "of decimals. We can't know if A's velocity is 5.0, 5.00, 5.001... etc. The exact quantity is irrelevant to the qualitative aspect, vA>vB. A velocity of 5.001 isn't really "Right" or "Wrong". It's "always right" in the sense that it is what you measured by definition, but it's always wrong in the sense that you can't state that the vA=5.00100000000000000000000000000000000.... (etc.)

**DaleSpam** · Nov7-09, 01:35 PM

Originally Posted by fhisicsstudnt

But no mathematical formalism does.

Then show me some credible reference about any specific aspect of light's behavior that QED does not accurately predict. Otherwise you are simply assuming something for which you have no evidence, just some weird anti-math prejudice.

Originally Posted by fhisicsstudnt

It may match to the 10th, 14th, 20th, etc. decimal place. Where one draws the line is subjective. 14 seems incredible right now, but the Borg are laughing at us, their instruments measure to 50 decimals and they can tell we're WAY off from the 15th decimal on. We're not even close to right! Another civilization rolls their eyes, they've characterized matter all the way down to the 1000th decimal place. The humans and Borg are both way, way off. Meanwhile God (Nature itself) "measures" an "infinite number" of decimal places.

The number of digits of precision for either our measuring devices or our computational methods is irrelevant here. The equations themselves have infinite precision.

Originally Posted by fhisicsstudnt

By visualization I mean visualizing the invisible actors in the play and how they behave to produce the observed phenomenon.

Very amusing, "visualizing the invisible actors"

Originally Posted by fhisicsstudnt

A moved faster than B, A hit the wall before B; qualitative

Both of these statements are also quantitative. If A moved faster than B then you must have some method of measuring the difference in speed. If the difference in speed is large enough then you can just use your eyes or some other coarse measurement apparatus, but for progressively smaller differences in speed you need progressively more precise measurements. Your "qualitative" statements don't seem any different to me than your "quantitative" ones, except that you used less precision in the qualitative ones (certainly not infinite precision).

I really don't understand your fixation on precision nor your anti-math bias.