Re: [Phys-L] treating force as a vector ... consistently

[Ken Caviness <caviness@southern.edu>]

Bob,

What definition of "simultaneous" are you using here?   I don't know of any definition that treats two events that are connected by a light ray (null geodesic) as simultaneous.  In fact, if one observer sees two events, A and B, as simultaneous, some will see A precede B and others will see A follow B, but no signal emitted at event A can be received at event B (or vice versa), all observers agree that the interval between the events is space-like, not time-like or light-like.  

Spacetime interval stuff, right?  If the interval between two events is space-like for one observer, it is space-like for all observers, and in one special reference frame the events are simultaneous: delta_t = 0.  If the interval between two events is time-like for one observer, it is time-like for all observers, and in one reference frame the events occurred at the same point in space.  And if any observer sees event A as the emission of a light-speed signal whose reception is event B, then all observers will measure the spacetime interval as light-like, the events cannot be simultaneous for anyone.

I'm a bit rusty, the event of my studying this material precedes, according to all observers, the present moment, and for some of us that time-like interval is measured in decades....

All the best, relatively speaking,

Ken

Kenneth E. Caviness, Ph.D.
Professor of Physics, Southern Adventist University

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@www.phys-l.org] On Behalf Of LaMontagne, Bob
Sent: Tuesday, 30 August, 2016 23:29
To: Phys-L@Phys-L.org; Moses Fayngold
Subject: Re: [Phys-L] treating force as a vector ... consistently

If the information travels at the speed of light, then aren't the "action" and "reaction" simultaneous in Space-Time?

Bob at PC
________________________________________
From: Phys-l <phys-l-bounces@www.phys-l.org> on behalf of Moses Fayngold <moshfarlan@yahoo.com>
Sent: Tuesday, August 30, 2016 10:48 AM
To: Moses Fayngold; Phys-L@Phys-L.org
Subject: Re: [Phys-L] treating force as a vector ... consistently

 <snip>
  I do not see the value of this axiom. As I said in one of my previous messages, "action-reaction" concept is most simple and fruitful only in classical and static situation, in which case the notion of their starting and ending together is meaningless. In more realistic situations involving dynamics this notion does not work or is, at best, not straightforward. Consider, for instance, an electron-positron pair production from collision of 2 neutral particles in the field of a distant proton. Each member of the newly-born pair immediately feels the field of the proton and experiences the corresponding action, but the proton will start feeling their field (and respective reaction) much later. So the axiom does not work for this system. It may work if we include the particles' interaction with each other's field as an intermediate agent, and the changes of the respective field momentum. But that would be no less complicated than the rocket-fuel-outgoing jet stream interactions in Scot  t's own example.
> > That last axiom means that the weight of a book can not be a force 
> > pair
> to the table's normal force. The book was interacting with the Earth 
> long before it was placed on the table.

<snip>
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