[Bill S]

A point is not a "something". It is by definition infinitesimal, and therefore smaller than any "thing".

Infinitesimal is by definition: “an indefinitely small quantity; a value approaching zero.” My thinking is that if it is a quantity, and not zero, it must be something, but I am neither a mathematician or a physicist.

Experience teaches that trying to forge any kind of link between this sort of mathematical concept and the “real world” leads nowhere.  Possibly a “put-down” type answer like:

A point on a line has no length. A point on a timeline has no duration. What's the problem?

Where does it go from there?  Perhaps try saying what the “problem” is.  It’s always good to answer a question.

I have no problem with either of those, in principle.  However, in practice, can you show me a point that has no length, but is still there?

Similarly, a point on a timeline that is defined as having no duration may be theoretically valuable, but both the timeline, and the point are mathematical tools.  What would be a physical example?

No reply.  This is not an isolated example; which makes me wonder if I am asking a pointless question?

[Bill S]

Small enough to be mathematically treated as one for the task at hand.

I love math, I just don't want it to be confused with physics.

You can’t lie with math.  But it greatly aids obfuscation. 

[Halc]

Similarly, a point on a timeline that is defined as having no duration may be theoretically valuable, but both the timeline, and the point are mathematical tools.  What would be a physical example?

No reply.  This is not an isolated example; which makes me wonder if I am asking a pointless question?

7:15 AM, GMT is a physical point in time.  It isn't an event, since the location of where it is 7:15 is not specified and hardly unambiguous.

A physical event is something like 2 billiard balls hitting, which yes, is a process, but one can narrow it to a point by specifying say the point of maximum force between the two objects.

Both these things can be treated as mathematical points in a discussion of physics.

[guest4091]

Halc #46;


My mistake for not catching the word "accelerating", gotta read slower!

One can argue that time exists if it is something that can be measured.

It's motion that is measured and labeled as 'time'. From early history: astronomical bodies in motion, to today's quantity of light waves.
[/quote]

Perhaps you can suggest nonexistent things that nevertheless are measured. [/quote]

Time.

Einstein allowed the definition of the time of event E to be relative to any frame of choice.

Yes he did, but the clock was 'local' from the point of observation, which becomes the basis for coordinate transformations..
A. Einstein, 1905 paper, par.1:
"It might appear possible to overcome all the difficulties attending the definition of ``time'' by substituting ``the position of the small hand of my watch'' for ``time.'' And in fact such a definition is satisfactory when we are concerned with defining a time exclusively for the place where the watch is located; but it is no longer satisfactory when we have to connect in time series of events occurring at different places, or--what comes to the same thing--to evaluate the times of events occurring at places remote from the watch."

Of course it is perfectly legit to say that all observations are caused by past events, and causes are necessarily somewhere within the past light cone of observation event b.

That's essentially what I meant. All your observations are 'now'. The fossil is also in its current/now state. Observing an image of a nova, the star is in an historical state. The difference is between a and b.
Thanks for the conversation.

[guest4091]

Bill S #49;

 My sticking point was that Phyti seemed to find a few milliseconds without time.

Medical research in the past three decades has revealed the brain has multiple processes periodic and not, that serve as clocks, for most of the biological functions. There is an overall lag between sensory input and the consciousness of events. There is a mind-time connection. Comatose patients, amnesia, brain damage, etc, all interfere with ability to correctly sense intervals of time, short or long.

[alancalverd]

Experience teaches that trying to forge any kind of link between this sort of mathematical concept and the “real world” leads nowhere. 

Far from it. A rigorous treatment of infintesimals leads to differential calculus, whence we get the whole world of classical physics, mesoscopic engineering and just about everything that distinguishes enlightened men from priests, politicians, philosophers and all the other human dross we scientists scrape off our shoes.

[set fair]

Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.

[Bill S]

7:15 AM, GMT is a physical point in time.  It isn't an event, since the location of where it is 7:15 is not specified and hardly unambiguous.

Thank you, you make one of my points more eloquently than I.  7:15 AM, GMT is a concept that, as far as I am aware, exists only in the minds of rational beings (apparently not universally); it is an invented “point” on an imaginary line that, conveniently, charts progress of/through time.  Time, itself, as we have been discussing, is somewhat ethereal.  It’s a relatively simple matter to propose a point of zero dimensions in such a scenario. 

A physical event is something like 2 billiard balls hitting, which yes, is a process, but one can narrow it to a point by specifying say the point of maximum force between the two objects.

This is probably the nearest anyone has come to identifying a physical point of zero dimensions.  Unfortunately, the point of maximum force between the two objects has no independent existence, so could hardly qualify as a physical object.

[alancalverd]

Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.

Oh come now! A cow is a bovine quadruped that moos and poos, with milk in the middle. Time is what separates sequential events. These are definitions. Only a philosopher would pretend not to know what a cow "is". Farmers and scientists have more important things to think about, because we work with animals and time.

[Bill S]

A rigorous treatment of infintesimals leads to differential calculus, whence we get the whole world of classical physics, mesoscopic engineering and just about everything that distinguishes enlightened men from priests, politicians, philosophers and all the other human dross we scrape off our shoes.

The original question remains unanswered.  Perhaps the cognoscenti believe they can blind with science/maths this “human dross” before superciliously scraping them from their shoes. 

Your post seems to say more about your personal prejudices than about the subject of the thread, but the former is something from which I would prefer to remain detached. 

[Bill S]

At some point, I think, I hijacked this thread. I don’t feel guilty about it because it has been a fruitful discussion, at least until recently.  I’ve gained a lot from it, and would like to thank those who have coped patiently with my persistence.  Unfortunately, the thread is showing signs of the sort of degeneration that one does not expect of TNS, so I am opting out. 

I’m pulling together some thoughts, which will undoubtedly raise even more questions/objections. 
I’ll probably post these in a new thread, rather than stay with this one.

[Halc]

7:15 AM, GMT is a concept that, as far as I am aware, exists only in the minds of rational beings (apparently not universally); it is an invented “point” on an imaginary line that, conveniently, charts progress of/through time.

I'd hesitate to call it a line.  7:15 happens at every point in space.  Different frames make it happen at different events, but there's damn few points in space where 7:15 doesn't happen at all.

The line could be your worldline, with a watch strapped to you defining 7:15.  That worldline is not at all imaginary because it is completely occupied by you, as is nowhere else.  That line (in particular the orientation of it at 7:15) defines 7:15 everywhere else at that event.

A physical event is something like 2 billiard balls hitting, which yes, is a process, but one can narrow it to a point by specifying say the point of maximum force between the two objects.

This is probably the nearest anyone has come to identifying a physical point of zero dimensions.  Unfortunately, the point of maximum force between the two objects has no independent existence, so could hardly qualify as a physical object.

Well I never suggested a point was physical object.  Heck, even physical objects are not physical objects when you get right down and dirty.  The event I described with the billiard balls has a nice defined location and time, so it seems to suffice.  But I agree, it isn't an object at all.

[PmbPhy]

For those who know algebra see the derivation at http://www.newenglandphysics.org/physics_world/gr/grav_red_shift.htm

It may help some to understand the phenomena. Colin got it perfectly in the second post. The math adds better precision to hos response. I.e. adds precision to the description.

[set fair]

Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.

Oh come now! A cow is a bovine quadruped that moos and poos, with milk in the middle. Time is what separates sequential events. These are definitions. Only a philosopher would pretend not to know what a cow "is". Farmers and scientists have more important things to think about, because we work with animals and time.

Fair enough they're definitions but I think definitions of elapsed time. What actual time is, we don't know. We don't understand the time line of particles involved in spooky action at a distance. We don't know if time is quantised.

[alancalverd]

At the risk of being dragged into philosophy, the notion of "elapsed" presumes a direction. We are fairly relaxed about the scalar distance between A and B and the vector distance from A to B, because the context makes it obvious and for the most part |A→B| = |A←B|, but it isn't always so.

If we accept Eddington's "entropy is time's arrow" then we have an independent definition of the directon of sequential events (positive if the entropy of the universe has increased between A and B) and hence a concept of elapsed time. But history, archaeology, carbon dating and the whole of forensic science, is about reconstructing events in reversed time, not merely establishing a sequence but also calculating the scalar modulus of temporal separation.

[alancalverd]

Not sure why entropy is frame-dependent. It is a scalar quantity whose increase denotes a conventional increase in time. A specific example would be radioactive decay.

If c is constant, we can always determine the sequence of events A and B.

[yor_on]

Well, we have Lorentz transformations giving us a 'eye of a God'.
What that means though is that although we have a logic defining SpaceTime we don't have answer to why it does it.

Unless logic is what makes a SpaceTime?

[guest47899]

the ironic time dichotomy.  time is a measure of motion.  in the case of absolute zero, freeze/stop the motion of a particle and you stop time/aging from progessing for that particle.  motion as expressed in velocity has the same result. accelerate that same particle to the SOL and you have effectively stopped time from progressing/aging for that same particle. 

cryogenics in time/space travel.

so, if you were able to freeze a particle to absolute zero where motion ceased completely in it, and then accelerate it to the speed of light; would the lack of motion/energy within it negate the SR requirement that when accelerating to the speed of light, mass/energy increases proportionally?

Consider that same particle traveling at the speed of light, would that same motionless hadron particle then be considered a bosonic field/force?

[jeffreyH]

Entropy is NOT frame dependent. The entropy will always increase by the same amount for the same process IN ANY FRAME. The time required to accumulate the entropy may vary but the entropy itself won't. As Alan said it is a scalar quantity.

[guest47899]

the ironic time dichotomy.  time is a measure of motion.  in the case of absolute zero, freeze/stop the motion of a particle and you stop time/aging from progessing for that particle.  motion as expressed in velocity has the same result. accelerate that same particle to the SOL and you have effectively stopped time from progressing/aging for that same particle. 

cryogenics in time/space travel.

so, if you were able to freeze a particle to absolute zero where motion ceased completely in it, and then accelerate it to the speed of light; would the lack of motion/energy within it negate the SR requirement that when accelerating to the speed of light, mass/energy increases proportionally?

Consider that same particle traveling at the speed of light, would that same motionless hadron particle then be considered a bosonic field/force?

so as not to cause confuse,  in the above please, substitute velocity of light for speed of light. doing so make the above a vector quantity rather than a scalar quantity.

without motion at absolute zero there no equalization of thermal energy, thereby rendering entropy a moot point.