Jump to content


Photo

A Request to the Physicists Among Us

  • Please log in to reply
98 replies to this topic

#26 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 11:02 AM

Let us now say the desk is stopped. Let's imagine something like it running into an asteroid. At the moment it stops, the desk loses the energy that had been added to it by my application of force. Correct?

Otto

#27 Ravenous

Ravenous

    Viking 1

  • -----
  • Posts: 638
  • Joined: 14 Nov 2009
  • Loc: UK

Posted 27 March 2013 - 12:09 PM

Some (most) of the energy is transferred to the asteroid. You pushed the desk originally, you see it go towards the asteroid and land/crash. If you have infinitely good measuring abilities, you will observe the asteroid (with the desk on it) is moving at a slightly different speed... the desk has shared its energy with the asteroid and changed its course.

When you stand on the earth and jump, the Earth bounces downwards too. (In theory - because I doubt it's ever been measured.)

#28 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 12:13 PM

Thank you Ravenous, EJN, Ira, and Jarad,

The desk gained energy when I shoved it. It lost that extra energy when it collided with the asteroid.

On the way (after the shove and before the collision) what was that energy? Was it a something? What was the nature of that something?

#29 llanitedave

llanitedave

    Humble Megalomaniac

  • *****
  • Posts: 22660
  • Joined: 25 Sep 2005
  • Loc: Amargosa Valley, NV, USA

Posted 27 March 2013 - 12:44 PM

Thank you Ravenous, EJN, Ira, and Jarad,

The desk gained energy when I shoved it. It lost that extra energy when it collided with the asteroid.

On the way (after the shove and before the collision) what was that energy? Was it a something? What was the nature of that something?


That's really a relative concept. The energy it "has" is relative to whatever energy the comparative object has. The energy it has relative to your body after pushing it is equal to the force at which you pushed it. The energy it has relative to the walls of whatever external object is in the vicinity is only half of what your push imparted, because the other half is you moving away from the desk.

The energy it has relative to the target asteroid is a factor of the vector of the two objects' directions. If they are moving exactly parallel to one another without intersecting, there is no kinetic energy to impart. If they are moving directly towards one another, then whatever energy you imparted to the desk (half the amount contained in your push) will be added to its impact with the asteroid.

#30 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 01:35 PM

Dave, thank you as always for taking on my basic questions!


There is this desk sitting motionless in the vacuum of space. It, the desk, is made up of whatever it is it is made.

Now the desk is shoved and it is moving through space. It has not yet impacted against anything. The desk is still the same desk but it is moving. Is this moving desk made up of exactly the same components of which it was constituted while it was sitting still. Or is it made up of the same components plus a "something"?

Is the force which caused it to move, somehow now a something within the object itself?

The desk is, at this moment different from the previous desk. The previous desk was a-motionless-desk. It is now a-desk-in-motion. There is nothing now in contact with it causing it to be in motion. Somehow, the originating force has been transferred into the desk, causing what was a-motionless-desk to be a-desk-in-motion. Is that something which is causing it to now (not when it was first pushed, but now) to be in motion, a constitutive part of the desk making it a desk+something? What is the something?

Otto

#31 Jarad

Jarad

    Fly Me to the Moon

  • *****
  • Posts: 6389
  • Joined: 28 Apr 2003
  • Loc: Atlanta, GA

Posted 27 March 2013 - 02:02 PM

It depends on your frame of reference.

The desk is made of matter, which has a fixed amount of rest mass (M0). The rest mass is intrinsic to it regardless of reference frame. To an observer sitting at the desk (at rest relative to it), its total mass is the same as its rest mass, and its kinetic energy is zero.

To an observer in a different frame of reference that is moving relative to the desk, it has kinetic energy. It also has a different total mass (M = M0 + E/C^2, where E is the kinetic energy). The clock sitting on the desk is also running slower to the observer moving relative to the desk than to the observer sitting at the desk.

So the energy is not intrinsic to the desk itself - it is a relative value that depends on what reference frame it is measured from. As far as the desk is concerned, it didn't change at all when you shoved it - you started moving away from it.

That's part of the core concept of relativity.

Jarad

#32 llanitedave

llanitedave

    Humble Megalomaniac

  • *****
  • Posts: 22660
  • Joined: 25 Sep 2005
  • Loc: Amargosa Valley, NV, USA

Posted 27 March 2013 - 02:06 PM

Right, the idea of either you or the desk being motionless is very much limited to you and the desk. It has no real meaning to the rest of the universe.

#33 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 02:18 PM

Long ago, when I was reading things like the Principia and Galileo's Two New World Sciences, I vaguely recall reading phrases such as "impressed force". The idea I took from this was their primitive way of understanding that the force which causes something to move does create a change in the substance of the thing being moved; much like a ring imprinting an image of a seal on the wax sealing a letter.

Using their old fashioned language, the difference between the motionless desk and the desk in motion is that the second, the desk in motion is the same as the motionless desk...but with an imprint; an actual change in the desk itself.

............

Second attempt:

Just before you wrote I, too, Jarad, was thinking of that formula from relativity (M = M0 + E/C^2). And yes, I understand that the difference of mass is dependent on the frame of reference.

But the fact is that the motion causes a change in the desk; its mass increases.

Now, recently, I have heard of a thing called the Higgs Boson which accounts for the mass of an object. If the mass of the desk has changed, there is then, so I undersstand, some difference in regard to the constitution of the desk-in-motion compared to the motionless-desk in terms of the Higgs Bosons constitutive to the two desks.

Am I correct?

#34 Jarad

Jarad

    Fly Me to the Moon

  • *****
  • Posts: 6389
  • Joined: 28 Apr 2003
  • Loc: Atlanta, GA

Posted 27 March 2013 - 02:45 PM

But the fact is that the motion causes a change in the desk; its mass increases.



But this isn't a change in the desk itself.

Let me give you a slightly different scenario - you are in a spaceship coasting along, and you gently release the desk outside the airlock. It is floating along next to you, no relative kinetic energy.

Now you fire up your engines to return to earth. You are now moving relative to the desk, and from your point of view it now has kinetic energy and its (non-rest) mass has changed.

Did the desk change? It's still floating along in the same orbit as it was before you used your engines.

Jarad

#35 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 02:49 PM

That's helpful.

I'm thinking.

#36 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 02:55 PM

Jarad,

Is there such a thing as rest-mass?

Otto

#37 Jarad

Jarad

    Fly Me to the Moon

  • *****
  • Posts: 6389
  • Joined: 28 Apr 2003
  • Loc: Atlanta, GA

Posted 27 March 2013 - 03:00 PM

Yes, rest mass is what we normally think of as just mass (since we don't usually encounter objects with enough velocity to measurably change their mass).

Rest mass does not depend on frame of reference.

Jarad

#38 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8237
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 27 March 2013 - 03:03 PM

I think you have to be careful here in two ways. One is that the mass of the object 'contains' energy (a sort of by definition of it being composed of matter), and there is the quantum and thermodynamic aspect of that. Then there is the treatment of mass as an object and here if you are saying 'at rest' you need to have some sort of reference frame for the aggregate object and the spacetime treatment. Rather than a desk there is a good example using a spring and that the spring one wound up should somehow increase in weight as there is now stored energy. So the spring should weigh more when wound than when unwound. This change in weight is predicted to be exceptionally small, but then measuring that spring on surface of earth we now have to account for all the forces in the spacetime field the spring resides in in both states. It may be at rest with respect to the test jig and lab, but not with respect to sun and moon. But the spring is an object that is an aggregate of mass. Things change fundamentally when we consider the atoms in the spring and their individual energy.



So it's a question of scale in ways energy at the extremely small and energy at the extremely large. There are and have been a lot of attempts to reconcile the two, at least in the last hundred or so years that's where all the fun is?

Maybe this link might help.

#39 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 03:14 PM

Jim/Jarad,

Thank you much.

Jim, I went to that website link. In it was written..."Now when people are describing the "mass" of different objects, including particles, it's much more convenient to talk about the rest mass, also called the "invariant mass", the mass a particle has in a frame in which its momentum is zero."


Does any given object exist in a multiplicity of different frames of reference at any given time; within some it has no momentum, but relative to the many others it does?

#40 Jarad

Jarad

    Fly Me to the Moon

  • *****
  • Posts: 6389
  • Joined: 28 Apr 2003
  • Loc: Atlanta, GA

Posted 27 March 2013 - 03:55 PM

I think it would be more accurate to say that the particle exists, and can be measured from any frame of reference. There is only 1 frame of reference in which it is at rest.

It's not that it exists in many different frames, it's that there are many different frames it could be measured from. There is only 1 object.

As a simpler analogy let's take measuring the distance to an object. There is only 1 location where the distance to it is zero (the location where the object itself is). There are an infinite number of other locations you could measure the distance to it from, and get a different answer for the distance. That doesn't mean the object exists at many different distances. The object is unique, but the distance to it can only be defined relative to something else.

Rest mass is a property of the object. Velocity, kinetic energy and therefore total mass can only be defined relative to something else, it's not an intrinsic property of the object.

Jarad

#41 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 27 March 2013 - 04:04 PM

I have to leave now to get to a family event. I have very much appreciated the primer in elementary physics through which each of you have taken the time to walk me.

I will be digesting these matters while I drive and will, undoubtedly, have other questions later.

Thank you.

Otto

#42 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 29 March 2013 - 11:58 AM

Lawrence Jacobsen continued:

He seems to have been influenced by Jacob Bronowski's Ascent-of-Man documentary.

Anyway, he cites a quote of the physicist, Max Born. I believe Schrodinger quoted Born making the statement which follows.

I would appreciate hearing from you physicists, professional and amateur, what you believe Born was saying, what he meant to communicate when he (Born) wrote,

"I am convinced that theoretical physics is actually philosophy."

Thank you.

Otto

#43 Joad

Joad

    Wordsmith

  • *****
  • Posts: 18176
  • Joined: 22 Mar 2005

Posted 29 March 2013 - 01:18 PM

I wouldn't take off-the-cuff statements by physicists (especially from the "golden age" of physics) too seriously. They were on to something really new (Quantum Mechanics especially) and realized that our thinking about reality would have to be realigned. Heisenberg went so far as to opine that reality had evaporated in the wake of QM (postmodernists have really jumped on this), but in another statement opined that QM could be related to what Aristotle had to say about the nature of dunamis, or potentiality (I jumped on that).

But in the end, while physicists have said all sorts of things that could be called philosophical, their actual practice is quite different from the practice of philosophy.

#44 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 29 March 2013 - 01:25 PM

Hi Joad,

My memory is a bit fuzzy...do I recall you writing here in response to my request, somewhat in depth, on the issue of potentiality as an aspect of reality , specifically; and hylomorphism in particular?

Your take on an intellectual generalist [Jacobsen], quoting Bronowski, perhaps quoting Schrodinger, quoting Born is pretty much what mine is.

Would you say that physicists today understand the basic principles of quantum physics to be as objectively true and understandable as physics' understanding of basic concepts of force and energy, say of a century ago?

#45 Joad

Joad

    Wordsmith

  • *****
  • Posts: 18176
  • Joined: 22 Mar 2005

Posted 29 March 2013 - 04:00 PM

Newtonian physics, which was of immense interest to philosophers, does not challenge our fundamental human perception/conception/construction of reality. So in that sense one might say that philosophers of the pre-Quantum, pre-Relativity era felt pretty confident about the whole thing.

But while QM and Relativity have also been of immense interest to many current philosophers of science, both QM and Relativity are so alien to our fundamental human perception/conception/construction of reality that their philosophical explorations rest on a far less firm ground. The main problem is that neither QM nor Relativity make much sense in the context of natural language conceptuality (which is the language of a philosopher); they only make sense in the language of mathematics. Most philosophers (if not all) do not really have the mathematical training to fully grasp QM and Relativity (I know that I don't), and even physicists who do have that training can run off the rails when speculating in natural languages on what mathematics reveal. The "strong" anthropogenic argument that our observation of a photon not only causes it to collapse into a wave packet but also causes its emission in the first place is an example, IMHO, of physicists running off the rails.

#46 EJN

EJN

    Vanguard

  • *****
  • Posts: 2256
  • Joined: 01 Nov 2005
  • Loc: 53 miles west of Venus

Posted 29 March 2013 - 05:52 PM

This is from the introduction to a course on quantum mechanics:

General relativity can be a difficult subject to master, but its mathematical
and conceptual structure involves a fairly straight-forward extension of structures
that characterize 19th century physics. The fundamental physical laws
(Einstein's equations for general relativity) are expressed as partial differential
equations, a familiar if difficult mathematical subject. The state of the system
is determined by the set of fields satisfying these equations, and observable
quantities are functionals of these fields. The mathematics is just that of the
usual calculus: differential equations and their real-valued solutions.

In quantum mechanics, the state of a system is best thought of as a different
sort of mathematical object: a vector in a complex vector space, the so-called
state space. One can sometimes interpret this vector as a function, the wavefunction,
although this comes with the non-classical feature that wave-functions are complex-valued.
What's truly completely different is the treatment of observable
quantities, which correspond to self-adjoint linear operators on the state
space. This has no parallel in classical physics, and violates our intuitions about
how physics should work.


In 1997, I attended a lecture at Fermilab by Nobel prize winner Murray
Gell-Mann, who developed the theory of quarks. He said something very memorable,
paraphrasing from memory:

"Some people find quantum mechanics weird or strange. Quantum mechanics is a
theory which makes very precise predictions which have been verified by experiment.
There's nothing weird about that. It's just quantum mechanics, being quantum
mechanics. That's all it does!"

On a PBS program, another physicist (whose name I don't remember) said (again,
paraphrasing from memory):

"Quantum mechanics is a theory whose predictions have been verified by experiment
to a precision almost unparalleled in physics. As for what it means, I leave that
to the philosophers. But personally, I think they have no idea what they are
talking about."




#47 Otto Piechowski

Otto Piechowski

    Apollo

  • -----
  • Posts: 1465
  • Joined: 20 Sep 2005
  • Loc: Lexington, KY

Posted 29 March 2013 - 08:48 PM

Joad and EJN...you two did a spectacular job of clarifying the issues regarding the objectivity and understandability of classical physics and QM/relativity physics.

Now, I would like to do a regular philosophical thing, of putting, side by side, two spectacular quotes by two physicsts (one, Max Born, and the other from the PBS program cited), and inviting whatever comments anyone wishes to make about the dialectic of these two statements.

Born: "I am convinced that theoretical physics is actually philosophy."

PBS: ""As for what it [quantum mechanics] means, I leave that to the philosophers. But personally, I think they have no idea what they are
talking about."

#48 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8237
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 29 March 2013 - 11:47 PM

PBS: ""As for what it [quantum mechanics] means, I leave that to the philosophers. But personally, I think they have no idea what they are
talking about."



I guess that shows PBS is seeking the same audience as the 'Jerry Springer' folks? (not the first time or subject IMO)

Some of the best set theoreticians and in ways mathmaticians /numerical analysis folks I have met have degrees in philosophy at the BS or PhD level. Study of logic can be a powerful thing. So consider that a moron can comment on anything (and for some reason the mass media seems to need that for it's 'controversy' angle...), but to argue with the moron folks might not be able to tell which is which? (just tagging onto an old saying there).. So my suggestion is to take that as PBS 'theatrics'.

#49 herrointment

herrointment

    Aurora

  • *****
  • Posts: 4922
  • Joined: 12 Mar 2011
  • Loc: East of Poskin

Posted 30 March 2013 - 05:23 PM

As an aside...I'm reading this thread and following along as well as can be expected. This thought crossed my mind....

At my job, during lunch, for 20 some odd years, the only thing my co-workers talk about are guns with a wife story tossed in here and there.

My brain needs exercise.

#50 Napersky

Napersky

    Vanguard

  • *****
  • Posts: 2038
  • Joined: 27 Jan 2010
  • Loc: Chicagoland

Posted 30 March 2013 - 08:28 PM

..and even physicists who do have that training can run off the rails when speculating in natural languages on what mathematics reveal. The "strong" anthropogenic argument that our observation of a photon not only causes it to collapse into a wave packet but also causes its emission in the first place is an example, IMHO, of physicists running off the rails.


I am and always have been suspicious of Special Relativity and statements made by Physicists about the nature of Quantum Mechanics as I was trained in Philosophy as a major at the undergraduate level. I agree with Joad that the above statement appears illogical.

After all Physicists are not Philosophers or Logicians. They seem to think that A and Not A can exist in the same time and space without special qualifications. (hyperbole)

"

"But in the end, while physicists have said all sorts of things that could be called philosophical, their actual practice is quite different from the practice of philosophy."

I hope the problems I have with some physicists statements are not real problems of the physics at all but just bad statements of philosophy uttered by these men to popularize and explain their theories to the lay public. :foreheadslap:

Mark






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics