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Size of an event in Spacetime


tar
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CollinJ simple unification theory has an analogy to my problem with spacetime events and possibly has similar resolutions, but I did not want to associate myself with collinj as that would be a handicap for CollinJ.   However we both have the same thought in terms of seeing something that goes against established theoretical math, and this morning I think I noticed the reason.

In relativity a spacetime event is defined or represented as a point in a manifold and transforms are made between two observers of the point in two different inertial frames.

The problem I have with this is an event is neither a point in space because it has a size, nor an instant in time, because it has a duration.  By definition an event requires both a change in a situation over time and a volume of space in which to occur.  So it would be an errored assumption to relegate an event to a dimensionless point.

Perhaps resolving the size and duration of the "point" would square or "cube" the equation to match reality.

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Don't you need a theory of quantum gravity to square the physical event with the mathematical model?

 

Events are very ,very small (like little Putina dolls)  and ,as far as I know have not been observed directly.

 

Edited by geordief
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13 minutes ago, tar said:

In relativity a spacetime event is defined or represented as a point in a manifold and transforms are made between two observers of the point in two different inertial frames.

Yes this is true.

An 'event' refers to a point with unique or particular coodinates in a given frame of reference.

15 minutes ago, tar said:

The problem I have with this is an event is neither a point in space because it has a size, nor an instant in time, because it has a duration.  By definition an event requires both a change in a situation over time and a volume of space in which to occur

This view has merit, not only in this situation but in many others besides.

16 minutes ago, tar said:

So it would be an errored assumption to relegate an event to a dimensionless point.

There are established mathematical techniques for handling the situation.

Either

We can show that the system of interest is 'small enough' to ignore its sizing in the coordiante system.
Sadly this is too often taken for granted or not done explicitly.

An example would be taking the Earth as a point particle in the solar system for the purpose of calculating obits etc.

or

We can use the mathematical limiting process to consider a 'control volume' in the coordinate system and tak the (mathematical) limit of the maths as we shrink the control volume to a zero sized point.

An example of this would be ordinary density which is a point function that is defined as such a limit.

 

 

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22 minutes ago, tar said:

Perhaps resolving the size and duration of the "point" would square or "cube" the equation to match reality.

Your not the size of an elephant, that's reality... 

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Who is CollinJ and why is this relevant?

 

2 hours ago, tar said:

The problem I have with this is an event is neither a point in space because it has a size, nor an instant in time, because it has a duration.  By definition an event requires both a change in a situation over time and a volume of space in which to occur.  So it would be an errored assumption to relegate an event to a dimensionless point.

Under what circumstances will this matter? If I am driving my car and say that I will arrive at some time T, does it matter that the front of my car arrives a fraction of a second earlier? No measurement has infinite precision.

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23 hours ago, swansont said:

Who is CollinJ and why is this relevant?

 

Under what circumstances will this matter? Ijf I am driving my car and say that I will arrive at some time T, does it matter that the front of my car arrives a fraction of a second earlier? No measurement has infinite precision.

CollinJ was another poster in this forum that suggested he found a way to unify the big and the small.

I did not want to hijack his thread nor associate myself with him as I thought such would prejudice those who are prejudiced against my thinking on this against his thinking on this.

Where I see it matters in what we experience about the world and its behaviors, is that we "see" using photons.  These little creatures are neither wave nor particle but have attributes of both.  A particle is hard to pin down, as one cannot determine both the location and the momentum of a particle.  You either know where it is or you know where it is going and where its been and how quickly it seems to be making the location change.  Or the photon can be thought of as a wave which has an amplitude and a frequency.   In both cases time and distance are required in order to describe the photon.    Since we "see" using photons, the size and duration of the experiment is important to consider, because there is a light travel time to consider from one end of the experiment to the other.

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44 minutes ago, tar said:

CollinJ was another poster in this forum that suggested he found a way to unify the big and the small.

I find no matches to a member with than username. The only hits on that are in this thread.

 

Quote

Where I see it matters in what we experience about the world and its behaviors, is that we "see" using photons.  These little creatures are neither wave nor particle but have attributes of both.  A particle is hard to pin down, as one cannot determine both the location and the momentum of a particle.  You either know where it is or you know where it is going and where its been and how quickly it seems to be making the location change.  Or the photon can be thought of as a wave which has an amplitude and a frequency.   In both cases time and distance are required in order to describe the photon.    Since we "see" using photons, the size and duration of the experiment is important to consider, because there is a light travel time to consider from one end of the experiment to the other.

I will ask again: Under what circumstances will this matter?

Alternately, give a pointer to an experiment where this would matter where it was not taken into account. I am familiar with experiments which use coincidence detection, so I know of experiments where this is explicitly taken into consideration, because circumstances dictate that.

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Perhaps I am worrying over nothing, if this is already taken into account, but to have a T=0 you have to know if that is according to the event location, the experimenter's location, or the coincident detector's location.  in the experiment it would be required to know the distances between all three and how their clocks were synced. 

for instance if a green leaf is falling the position of the leaf is different for someone a meter away and someone 2 meters away

a milli second after the first guy sees it fall the guy standing a meter behind him sees it fall.   When the second guy sees the first wave edge the first guy is seeing the hundred millionth wave edge, if the wavelength of green light is 500nm.

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1 hour ago, tar said:

Perhaps I am worrying over nothing, if this is already taken into account, but to have a T=0 you have to know if that is according to the event location, the experimenter's location, or the coincident detector's location.  in the experiment it would be required to know the distances between all three and how their clocks were synced. 

for instance if a green leaf is falling the position of the leaf is different for someone a meter away and someone 2 meters away

a milli second after the first guy sees it fall the guy standing a meter behind him sees it fall.   When the second guy sees the first wave edge the first guy is seeing the hundred millionth wave edge, if the wavelength of green light is 500nm.

If it’s meters the time will not be milliseconds. c = 3 x 10^8 m/s. meters means nanoseconds. 

This issue is as I had mentioned. When I did my postdoc at TRIUMF, the cables were labeled in nanoseconds, so you could account for the signal delay time from different detectors. It’s not that you are worrying over nothing, it’s that you’re not pointing out something that others have missed, and you are framing it as such.

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Understood

did you e er work with fiber optic cable or was it copper

I still don't think the logic is always sound.

That is, one person might be making assumptions the other is not and vice a versa.

What happens in the environment of the Earth, pretty much happens within the time it takes a light signal to get from one place to another.  That is, we more or less can consider ourselves in the same moment.  It takes time for a signal from our eye to get to our brain and such, so nothing is immediate.  There is a fudge factor we commonly apply to consider something happening "at the same time", but for the sake of this discussion in terms of the size of an event, I think it worth while to consider the real difference between one side of an event and another.  For instance, when someone says the event is happening now are they talking the leaf starting to fall, or the light striking the ccd recording the event?

Cosmic events are even harder to agree upon the event size, because in a real sense, if you are just now seeing a super nova, it has both already happened, maybe 10 of thousands or millions of years ago, AND is actually still occurring because a photon from it, just hit your instrument. 

 

to relegate a super nova to a dimensionless point in a spacetime manifold would be sort of meaningless

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8 hours ago, tar said:

Understood

did you e er work with fiber optic cable or was it copper

I still don't think the logic is always sound.

I've worked with copper, fiber and free-space transmission. The concept is the same.

 

8 hours ago, tar said:

That is, one person might be making assumptions the other is not and vice a versa.

What happens in the environment of the Earth, pretty much happens within the time it takes a light signal to get from one place to another.  That is, we more or less can consider ourselves in the same moment.  It takes time for a signal from our eye to get to our brain and such, so nothing is immediate.  There is a fudge factor we commonly apply to consider something happening "at the same time", but for the sake of this discussion in terms of the size of an event, I think it worth while to consider the real difference between one side of an event and another.  For instance, when someone says the event is happening now are they talking the leaf starting to fall, or the light striking the ccd recording the event?

And once again I will ask if you have example of this not happening when it matters. Because I don't have any — people working on experiments that require precise measurements do these things, otherwise their experiments don't work. 

You're pointing out the obvious

 

 

8 hours ago, tar said:

Cosmic events are even harder to agree upon the event size, because in a real sense, if you are just now seeing a super nova, it has both already happened, maybe 10 of thousands or millions of years ago, AND is actually still occurring because a photon from it, just hit your instrument. 

Unlikely that a supernova event 10000 LY away is still occurring if we're just getting the photons now. We know how long supernovae last, and it's much less than 10,000 years.

 

8 hours ago, tar said:

to relegate a super nova to a dimensionless point in a spacetime manifold would be sort of meaningless

Let's say it was 10,000 LY away, and the star was 30 light-seconds across (which is about 9 million km; the sun is about 1.4 million km across) A year is a little over 3 x 10^7 sec, so the distance ratio is 30s *c/10^4 * 3x10^7 *c

Ignoring the size gives an error of a part in 10^10, so in some cases this is meaningless — if your experiment has less precision than this.

The bottom line is that the speed of light is a known phenomenon and physicists aren't stupid, and your premise is basically that they/we are (and we see similar "point out obvious things" phenomena in discussions on evolution, too).

On top of that, we have peer review, so even if one particular experimenter somehow ignored the effect, others would notice when it came time to publish results, either through peer review or in responses to the publication, which would be quickly retracted from any reputable journal. So unless you have actual examples of people screwing up by not accounting for light travel, this is pointless, and just an exercise in you demonstrating that you have no familiarity with how these experiments are conducted.

 

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On 11/9/2021 at 5:39 PM, tar said:

a milli second after the first guy sees it fall the guy standing a meter behind him sees it fall.   When the second guy sees the first wave edge the first guy is seeing the hundred millionth wave edge, if the wavelength of green light is 500nm.

I would just like to point out that there is only one 'wavefront'  -  a better term than  wave edge.

This demarcates the boundary between the zone of space occupied by the wave and the zone where the wave has not yet reached.

 

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On 11/10/2021 at 7:22 AM, swansont said:

I've worked with copper, fiber and free-space transmission. The concept is the same.

 

And once again I will ask if you have example of this not happening when it matters. Because I don't have any — people working on experiments that require precise measurements do these things, otherwise their experiments don't work. 

You're pointing out the obvious

 

 

Unlikely that a supernova event 10000 LY away is still occurring if we're just getting the photons now. We know how long supernovae last, and it's much less than 10,000 years.

 

Let's say it was 10,000 LY away, and the star was 30 light-seconds across (which is about 9 million km; the sun is about 1.4 million km across) A year is a little over 3 x 10^7 sec, so the distance ratio is 30s *c/10^4 * 3x10^7 *c

Ignoring the size gives an error of a part in 10^10, so in some cases this is meaningless — if your experiment has less precision than this.

The bottom line is that the speed of light is a known phenomenon and physicists aren't stupid, and your premise is basically that they/we are (and we see similar "point out obvious things" phenomena in discussions on evolution, too).

On top of that, we have peer review, so even if one particular experimenter somehow ignored the effect, others would notice when it came time to publish results, either through peer review or in responses to the publication, which would be quickly retracted from any reputable journal. So unless you have actual examples of people screwing up by not accounting for light travel, this is pointless, and just an exercise in you demonstrating that you have no familiarity with how these experiments are conducted.

 

understood,  but I am not calling anybody stupid.  I agree the things happen the way people see them happen and report on them and figure them and such, but the assumptions vary.  For instance you say the super nova is no longer happening.  In one sense it is, because we are seeing it.  In another sense it is not because it happened in that location in space a long time ago and something else is happening now in that location in space.  But in order to understand this obvious fact about the universe you have to consider there are two nows and you told me that is not how it is...but that is how it is, so what is obvious? 

studiot I take your point about the term wavefront, but for this discussion the size of the wave matters too, in the sense that the size of a sine wave includes the measurement from peak to peak I think or valley to valley.  But where does a wave start? At the zero point.  When a photo is created by the drop of an electron from one energy level to another, this is a process or an event so to speak that in not instantaneous  would argue, but happens over a short period of time.  The wave edge starts as soon as the electron "starts" to fall and the whole fall creates a photon of said energy and frequency.

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1 hour ago, tar said:

understood,  but I am not calling anybody stupid.  I agree the things happen the way people see them happen and report on them and figure them and such, but the assumptions vary.  For instance you say the super nova is no longer happening.  In one sense it is, because we are seeing it.  In another sense it is not because it happened in that location in space a long time ago and something else is happening now in that location in space.  But in order to understand this obvious fact about the universe you have to consider there are two nows and you told me that is not how it is...but that is how it is, so what is obvious? 

Plenty of scientists understand this without considering the idea of “two nows” 

The shortcoming, it would appear, lies with your understanding of relativity. Perhaps you should consider addressing that, and not bringing up the speculations topic that’s been locked.

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Swansont,

That is your loss to lock that thread topic.   I cannot relay my understanding of relativity without using the two nows.  You use them all the time.  i am in no way saying the equations of relativity don't work.  I am saying I understand relativity and I can explain the math without requiring space to deform or time to dilate.

Regards, TAR

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31 minutes ago, tar said:

That is your loss to lock that thread topic.   I cannot relay my understanding of relativity without using the two nows.  You use them all the time.  i am in no way saying the equations of relativity don't work.  I am saying I understand relativity and I can explain the math without requiring space to deform or time to dilate.

I suppose we will just have muddle through the rest of our lives relying on mainstream physics. 

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Not going to work Bufofrog.  You wind up thinking the universe is weird, time dilates, distances shorten and there is dark energy and dark matter that we never needed before to explain mainstream physics.

but fine, go ahead and muddle

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1 minute ago, tar said:

Not going to work Bufofrog.  You wind up thinking the universe is weird, time dilates, distances shorten and there is dark energy and dark matter that we never needed before to explain mainstream physics.

I appreciate your concern, but like I said we will just put on a brave face and muddle through as best we can.

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bufofrog,

I don't understand why critical thinking is banned on this board.  

There is usually more than one way to explain a thing.  I do not accept foreshortening, because it deforms reality.  Pi for instance is not effected by velocity.

However if your spaceship traveling at close to c traverses a circle, the circle becomes an ellipse with no cause and effect noted, or any concern for whether the circle becomes an ellipse for everybody, or just for the moving observer.  If it happens just for the moving observer then the distant clock just appears to click differently, it does not actually tick differently.   If you apply common sense to any observation, hold time as clicking off equally everywhere at once and factor in the light travel time between the two ends of the experiment, and the position of the observers and the position of the experimenter, you can resolve differences in observed time without requiring the universe to do magic tricks.

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1 hour ago, tar said:

Swansont,

That is your loss to lock that thread topic.   I cannot relay my understanding of relativity without using the two nows.  You use them all the time.  i am in no way saying the equations of relativity don't work.  I am saying I understand relativity and I can explain the math without requiring space to deform or time to dilate.

Regards, TAR

 

!

Moderator Note

If you are able to explain the idea, you should have done so when you had the chance. But you did not, and continuing to raise this issue is against the rules.

You can insist that you understand relativity, but the evidence is that you do not.

 
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