Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: geordief on 15/03/2019 02:51:32
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I understand that an "event" is used to mean a point on a spacetime coordinate system or it can be one element of the set of aĺl events (which doesn't help).
But if we take an event as a physical oçcurence , what can we say about it?
If a particle is moving through the vacuum does an event only occur when it interacts with another object and are there no events between the start of its life and this interaction?
It can travel all the way across the universe without encountering any events?
Or do particles interact with themselves in any way and would that be an "event" ?
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If a particle is moving through the vacuum does an event only occur when it interacts with another object and are there no events between the start of its life and this interaction?
We define what an event is. Usually it is when something happens and we can define the point at which it happens as a spacetime coordinate. The happening can be anything, an object passing a point, changing speed, hitting something, emitting a photon, etc. You name it ;)
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I would use the word to indicate the boundary in spacetime where a change occurs between "before" and "after", as distinct from a spatial boundary between "here" and "there", a material boundary between "this" and "that", or a temporal boundary between "then" and "now".
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Alan, I’m trying to clarify the distinction between “spacetime where a change occurs between "before" and "after",” and “a temporal boundary between "then" and "now".”
In the case of Geordie’s particle travelling through the vacuum: at t1 it is at position 1; at t2 it is at position 2; between these is a temporal boundary, which you do not define as an event. (?)
What additional factor must be present to make this a “boundary in spacetime where a change occurs between "before" and "after",”?
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We define what an event is.
Would it be that all observers would agree on the occurrence of a spacetime event, but would not all agree on its timing, as that would depend on their individual reference frames?
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We define what an event is. Usually it is when something happens and we can define the point at which it happens as a spacetime coordinate. The happening can be anything, an object passing a point, changing speed, hitting something, emitting a photon, etc. You name it
So no restrictions? Can events fit inside one another like Russian dolls?
For example the fall of Rome could be an event that seems one dimensional from a distance and reveals "sub events" as one approaches.
Is that process relevant in physics?
Also is the location of a "fundamental" event viewed mathematically as the intersection of two or more surfaces of simultaneity ?
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Alan, I’m trying to clarify the distinction between “spacetime where a change occurs between "before" and "after",” and “a temporal boundary between "then" and "now".”
Midnight on 31 December 1999 was a temporal boundary between then and now, but to everyone's amazement, no planes fell out of the sky and Beelzebub did not claim his earthly inheritance, so it was a non-event. Even the London fireworks were disappointing, and the Dome was complete crap.
In the case of Geordie’s particle travelling through the vacuum: at t1 it is at position 1; at t2 it is at position 2; between these is a temporal boundary, which you do not define as an event. (?)
If you observed it at either point, that would have been an event because there would be a bit more information in the universe, so a distinction between before and after.
What additional factor must be present to make this a “boundary in spacetime where a change occurs between "before" and "after",”?
"after" must be distinguishable from "before": the new universe must not map exactly onto the old one.
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So no restrictions? Can events fit inside one another like Russian dolls?
Points don't fit inside each other, but a particle traces a path of points along its way, so those are all events even if no interaction takes place at most of them.
For example the fall of Rome could be an event that seems one dimensional from a distance and reveals "sub events" as one approaches.
This is using a different definition of 'event'. Rome did not fall at a point in spacetime. Rome is larger than a point, and the process took (a lot of) time.
Also is the location of a "fundamental" event viewed mathematically as the intersection of two or more surfaces of simultaneity ?
Two 3D hyper-surfaces of simultaneity will form a 2D plane of events which are simultaneous in both frames. All a third hyper-surface and that plane it reduced to a line. A 4th one reduces it to one event, meaning with four different inertial frames, no two events are simultaneous in all of them.
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Am I right to suppose that an event in quantum theory is a different to an event in Relativity?
Is an event in Quantum Theory perhaps the same as an observation?
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Am I right to suppose that an event in quantum theory is a different to an event in Relativity?
The 'point in spacetime' seems universal across physics, but QM may additionally leverage that word to indicate an occurrence of some state change like the decay of a nucleus, which for most practical purposes takes place at a spacetime point. I'm no expert on QM terminology.
Is an event in Quantum Theory perhaps the same as an observation?
It depends on the context I suppose. Usually 'observation' is an epistemological change, typically of a human learning the result of a measurement. A measurement is one system acquiring information about another system, hence changing the state (wave function) of the measured system. The exact wording is very interpretation dependent, and hence are metaphysical differences, not scientific ones.
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suppose. Usually 'observation' is an epistemological change, typically of a human learning the result of a measurement. A measurement is one system acquiring information about another system, hence changing the state (wave function) of the measured system. The exact wording is very interpretation dependent, and hence are metaphysical differences, not scientific ones.
I think I am more familiar with "observation" and " measurement" being synonymous ** -so that no actual acquisition of knowledge is implied simply ,perhaps a change of state in one system being directly connected to a change of state in another system.
But my understanding of Quantum Theories is flimsy.
**and "measurement" perhaps being synonymous with "interaction".
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Usually it is when something happens and we can define the point at which it happens as a spacetime coordinate.
A point is zero dimensional; so, if an event is something that happens at a point, the notion of an event is an idealisation, because the point at which it happens has no physical extent, but the actual event must have a finite extent. (?)
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The mathematical "events" could be approximately centred wrt the physical events (however they are described)
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A point is zero dimensional; so, if an event is something that happens at a point, the notion of an event is an idealisation, because the point at which it happens has no physical extent, but the actual event must have a finite extent. (?)
An event is a mathematical point which has no extent. Sure, this is an idealization. One can talk about the event of departure of a twin in the twins experiment, and for the purposes of the discussion, that event is treated as a point in spacetime.
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Simple particles like a photon or an electron don't interact with themselves to change state.
More complex particles like a neutron, or a plutonium nucleus or a hand grenade (with no pin) could spontaneously decay, and this could be considered an "event".
You could consider a photon passing through a glass window as an event, even if that particular photon did not interact with the glass in any dramatic way (more of a non-event).
And you could consider a photon (or a cat) passing through the event horizon of a supermassive black hole as an event (from the viewpoint of a distant observer), even though nothing special happens to the photon/cat (from it's viewpoint).
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But is the cat dead or alive?
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An event is a mathematical point which has no extent. Sure, this is an idealization. One can talk about the event of departure of a twin in the twins experiment, and for the purposes of the discussion, that event is treated as a point in spacetime.
An event may be well described as “a mathematical point which has no extent”, but as you say, “this is an idealization”. The idealisation has no physical extent, but the physical event it describes does. The “departure of a twin in the twins experiment” happens in time.
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I think you just echoed what I just said, yes.
What is it they say about imitation? :)
Actually it was: that event is treated as a point in spacetime.
I thought you were equating an event with a point.
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Actually it was: that event is treated as a point in spacetime.
I thought you were equating an event with a point.
Lots of things that are not points are treated as such. Earth is X many km from the sun. Never seen a page that listed it as a range (except when speaking of aphelion and perihelion, which are still point references).
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An event is a mathematical point which has no extent. Sure, this is an idealization.
For many purposes an approximation is fine. eg the Earth is an extended object, thousands of km across, which you could approximate as the center of the Earth; knowing this location within 1km is fine (unless you are a GPS satellite).
Similarly, for a cat entering a supermassive black hole, measuring the position of a cat within 100m may be enough. If you want more accuracy, you could measure from the center of mass of the cat, or the center of the pupil of its left eye.
But is the cat dead or alive?
For extended objects like a cat, there is not only an uncertainty in space, there is an uncertainty in time as well.
Quantum theory says that there will always be some uncertainty in space and/or time...
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But is the cat dead or alive?
To summarise quantum physics in one word, "yes".
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But is the cat dead or alive?
To summarise quantum physics in one word, "yes".
Now that answer I like.
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I understand that an "event" is used to mean a point on a spacetime coordinate system or it can be one element of the set of aĺl events (which doesn't help).
But if we take an event as a physical oçcurence , what can we say about it?...
It is something which has a spatial point location at an instant of time. Events are pretty much fictional in practice on a large scale because real objects are not point objects and have spatial extent. They apply more aptly in particle physics. This does not mean that events don't occur and can't be described on the large scale though. They're approximations in that case like a circle is not exactly what the top of a tuna can is. :)
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I understand that an "event" is used to mean a point on a spacetime coordinate system or it can be one element of the set of aĺl events (which doesn't help).
But if we take an event as a physical oçcurence , what can we say about it?...
It is something which has a spatial point location at an instant of time. Events are pretty much fictional in practice on a large scale because real objects are not point objects and have spatial extent. They apply more aptly in particle physics. This does not mean that events don't occur and can't be described on the large scale though. They're approximations in that case like a circle is not exactly what the top of a tuna can is. :)
An event is definitely something that happens in a region of space and time, and can encompass multiple interactions, as a result of an initial trigger event. The inflationary stage preceding the Big Bang was an event, that covered a period of time whereby particles came into existence, before resulting in a hot big bang and the slowing of the inflationary stage, which is now accelerating as g >0.
I am not so sure a tin of tuna can be described as an event :) although I suppose they happen to come into existence at a point in space and time, which could be a little chaotic as some have circular lids and others rectangular. The contents may result in different flavours on a galactic scale :)
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An event is definitely something that happens in a region of space and time,
That's not how the term event is defined. An event is a point in space at an instant in time, i.e. = (t, x, y, z) is an event.
The inflationary stage preceding the Big Bang was an event, ..
Wrong. Please read the definition of event at
https://en.wikipedia.org/wiki/Event_(relativity)
I am not so sure a tin of tuna can be described as an event ..
It can't. Its an analogy of how a geometrical object only approximates something in reality. That's why I said that the top of a tuna can is not a circle even though it looks like one or is measured to be one on a macroscopic scale.
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The inflationary stage preceding the Big Bang was an event, that covered a period of time whereby particles came into existence, before resulting in a hot big bang and the slowing of the inflationary stage, which is now accelerating as g >0.
I don't think any cosmologist would refer to the inflationary stage (which followed the big bang) an event. It is an epoch, which implies a significant period of time. It is no more an event than is the Holocene epoch which is currently ending. And while the inflation epoch was certainly of shorter duration than the Holocene, it represented a far greater percentage of the entirety of the history of time while it was going on.
I am not so sure a tin of tuna can be described as an event
It was being compared to something that is approximately round, just like the sinking of the Titanic is treated approximately as a point event.
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I don't think any cosmologist would refer to the inflationary stage (which followed the big bang) an event. It is an epoch, which implies a significant period of time. It is no more an event than is the Holocene epoch which is currently ending. And while the inflation epoch was certainly of shorter duration than the Holocene, it represented a far greater percentage of the entirety of the history of time while it was going on.
This is of thread, but I may start a thread to discuss this.
According to a couple of speculative theories I have read, the inflationary stage came first and caused virtual particles to become separated and become real particles. A little like Hawking radiation. Further more these particles decayed to become stable particles, giving off lots of heat creating the hot big bang. The concept of Aeons conformal cyclic cosmology by Roger Penrose tends to side step singularities and Big Bangs, but does require inflation as g>0.
Do you have a reference for your comment above. The term Big Bang is term which seems to have evolved since Hoyle coined the phrase and means a lot to different people. In particular I am interested in reference to the time duration of the inflationary stage ie what do you mean by Significant time
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An event is definitely something that happens in a region of space and time,
That's not how the term event is defined. An event is a point in space at an instant in time, i.e. = (t, x, y, z) is an event.
The inflationary stage preceding the Big Bang was an event, ..
Wrong. Please read the definition of event at
https://en.wikipedia.org/wiki/Event_(relativity)
Correct link https://en.wikipedia.org/wiki/Event_(relativity)
From your link "an event is the instantaneous physical situation or occurrence associated with a point in spacetime"
From the oxford English dictionary an event in physics is
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1.3Physics A single occurrence of a process, e.g. the ionization of one atom.
Example sentences
‘The aim of induction is to find series of events whose frequency of occurrence converges toward a limit.’
‘Consider our passage through time as riding the shockwave of the bang event.’
‘In the lower graph the current scale is amplified so that single channel events can be distinguished.’
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The Big Bang according to the oxford English dictionary was an event
https://en.oxforddictionaries.com/definition/event
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An event is definitely something that happens in a region of space and time,
That's not how the term event is defined. An event is a point in space at an instant in time, i.e. = (t, x, y, z) is an event.
The inflationary stage preceding the Big Bang was an event, ..
Wrong. Please read the definition of event at
https://en.wikipedia.org/wiki/Event_(relativity)
Correct link https://en.wikipedia.org/wiki/Event_(relativity)
From your link "an event is the instantaneous physical situation or occurrence associated with a point in spacetime"
From the oxford English dictionary an event in physics is
"
1.3Physics A single occurrence of a process, e.g. the ionization of one atom.
Example sentences
‘The aim of induction is to find series of events whose frequency of occurrence converges toward a limit.’
‘Consider our passage through time as riding the shockwave of the bang event.’
‘In the lower graph the current scale is amplified so that single channel events can be distinguished.’
"
The Big Bang according to the oxford English dictionary was an event
https://en.oxforddictionaries.com/definition/event
Strict definitions in physics should never be taken from a dictionary. I wrote the glossary to a GR text before so I know how event is defined in SR/GR. I know SR very well and GR nearly as well. Look in any SR or GR text and you'll see that I'm write. Being a physicist myself the precise definition is second nature to me. Wikipedia is a lot more dependable than a dictionary when it comes to science.
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Do you have a reference for your comment above. The term Big Bang is term which seems to have evolved since Hoyle coined the phrase and means a lot to different people. In particular I am interested in reference to the time duration of the inflationary stage ie what do you mean by Significant time
A knowledge of what an event and epoch is is proof enough. E.g., from Spacetime and Geometry by Sean Carroll page 4
Spacetime is a four-dimensional set, with elements labeled by three dimensional of space and one of time.
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A point in spacetime is called an event.
Notice the qualifier "point".
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I don't think any cosmologist would refer to the inflationary stage (which followed the big bang) an event.
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And while the inflation epoch was certainly of shorter duration than the Holocene, it represented a far greater percentage of the entirety of the history of time while it was going on.
This is of thread, but I may start a thread to discuss this.
Under that model, it is quite debatable as to which moment to assign the term 'big bang'.
According to a couple of speculative theories I have read, the inflationary stage came first and caused virtual particles to become separated and become real particles. A little like Hawking radiation. Further more these particles decayed to become stable particles, giving off lots of heat creating the hot big bang. The concept of Aeons conformal cyclic cosmology by Roger Penrose tends to side step singularities and Big Bangs, but does require inflation as g>0.
Do you have a reference for your comment above.
It seems to be fairly common understanding. A quick search picks this random page:
www.worldsciencefestival.com/2015/07/cosmological-inflation-primer/
For example, there are some puzzling features of our universe that can only be explained, some scientists argue, by the idea that our universe went through a short period (from somewhere in the vicinity of about 10−33 to 10−32 seconds after the Big Bang) of rapid expansion (by what scientists believe to be around a factor of 1026) after it emerged into existence. This idea is known as the theory of inflation, and is a widely accepted but still debated part of our universe’s beginnings.
My bold. Picture depicts this. Big bang is the singularity at left, the beginning of time as we know it. After inflation, space has expanded by 1026, which admittedly admits that the beginning wasn't a singularity or the size of the universe would be bounded.
It says it is debated, and there is eterial-inflation multiverse theory that says that inflation was outside the big bang, but bubbles of regular space-time condense out of that. I think that might be what you reference. Under that theory, inflation is still going on and did not terminate after this short time.
With eternal inflation, it becomes debatable which 'moment' or process to assign the term 'big bang'.
In particular I am interested in reference to the time duration of the inflationary stage ie what do you mean by Significant time
Well, if you put time zero at the left point and have finite inflation epoch terminating after 10-32 seconds, that short blip of time represents the entire history of the universe up to that point, as opposed to the Holocene which represents 2 millionths of Earth history. So that's a long time on a percentage basis.
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Strict definitions in physics should never be taken from a dictionary. I wrote the glossary to a GR text before so I know how event is defined in SR/GR. I know SR very well and GR nearly as well. Look in any SR or GR text and you'll see that I'm write(right :)). Being a physicist myself the precise definition is second nature to me. Wikipedia is a lot more dependable than a dictionary when it comes to science.
I do not doubt you. Being primarily English speaker and reading a lot of Pop Science as well as some good science, Am I wrong in thinking a Big Bang "event" happened 13.8 billion years ago.
I need to check this ! But I think it was Sean Carrol that published some interesting stuff recently, on Emergent Space time. Which does not have a hot big bang before the inflationary period. Further more a number of "speculatative" papers onm arxiv exist that indicate it was the inflationary stage of the universe that likely caused the Hot Big Bang.
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It seems to be fairly common understanding. A quick search picks this random page:
www.worldsciencefestival.com/2015/07/cosmological-inflation-primer/
For example, there are some puzzling features of our universe that can only be explained, some scientists argue, by the idea that our universe went through a short period (from somewhere in the vicinity of about 10−33 to 10−32 seconds after the Big Bang) of rapid expansion (by what scientists believe to be around a factor of 1026) after it emerged into existence. This idea is known as the theory of inflation, and is a widely accepted but still debated part of our universe’s beginnings.
My bold. Picture depicts this. Big bang is the singularity at left, the beginning of time as we know it. After inflation, space has expanded by 1026, which admittedly admits that the beginning wasn't a singularity or the size of the universe would be bounded.
It says it is debated, and there is eterial-inflation multiverse theory that says that inflation was outside the big bang, but bubbles of regular space-time condense out of that. I think that might be what you reference. Under that theory, inflation is still going on and did not terminate after this short time.
With eternal inflation, it becomes debatable which 'moment' or process to assign the term 'big bang'.
I am not sure how many infaltionary theories there are. I know there are more than a few, starting out with Guth then onto Lindes later ideas. Penroses ideas are another take on inflation, whereby he introduces Aeons. Having the universe go through multiple inflationary stages, and Big Bangs, does away with a singularity and a beginning or end of time.
Not being an expert, the number of different competing theories out there is mind boggling, I like Penroses theory because, it does away with singularities and a beginning to time, which does not ride well with me.
There also a number of competing theories as to what caused matter to come into existence. All the ones I have seen show it coming into existence in the inflationary stage, via the dynamic casimir effect, (recently proven) unruh effect (theoretical) similiar to Hawking radiation (theoretically plausible). That of course does not preclude other possible mechanisms, which I hope to learn more about.
Looking at the link you posted I still think inflation came before a hot big bang :)
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Chances are, you've all seen this, but just in case.......
https://profmattstrassler.com/articles-and-posts/relativity-space-astronomy-and-cosmology/history-of-the-universe/hot-big-bang/
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Strict definitions in physics should never be taken from a dictionary. I wrote the glossary to a GR text before so I know how event is defined in SR/GR. I know SR very well and GR nearly as well. Look in any SR or GR text and you'll see that I'm write(right :)). Being a physicist myself the precise definition is second nature to me. Wikipedia is a lot more dependable than a dictionary when it comes to science.
I do not doubt you. Being primarily English speaker and reading a lot of Pop Science as well as some good science, Am I wrong in thinking a Big Bang "event" happened 13.8 billion years ago
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Yes. That assumes there was an event called "big bang" but that's a myth. In modern cosmology there is no such event because there's no way to adduce such an event. Its based on an extrapolation. There are a lot of myths in pop physics. This one is explained in Peebles text on cosmology. Would you like me to quote that passage of his text?
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Chances are, you've all seen this, but just in case.......
https://profmattstrassler.com/articles-and-posts/relativity-space-astronomy-and-cosmology/history-of-the-universe/hot-big-bang/
Thanks for that Bill, according to the link inflation may have come first, resulting in the hot expansion.
"The Hot Big Bang may have begun when the universe became hot following a period of inflation, as explained in my article on the Era of Inflation. If so, the heat of the Hot Big Bang came from the dark energy that powered inflation, and the maximum temperature of the Hot Big Bang is related to the amount of dark energy that was available."
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Thanks for that Bill, according to the link inflation may have come first, resulting in the hot expansion.
It seems that the hot big bang description just assigns the term 'big bang' to the hot part after the inflation instead of the compact part that precedes the inflation. The hot part is, after all, the part that 'bangs' the loudest, so to speak.
In that case, the term big bang is not being assigned to something that meets the definition of an event.
Surely the hot-big-bang terminology is also a different theory in some way, and not just a reassignment of terms, but I actually get from the linked article that it is merely a reassignment of terms and not anything new. It does correct the notion that the universe was 'hot' during inflation. The old text always described the initial singularity as an infinitely dense and hot point, but it is neither. That old idea sort of went away when they realized the total energy of the universe was probably zero.
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Am I wrong in thinking a Big Bang "event" happened 13.8 billion years ago
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Yes. That assumes there was an event called "big bang" but that's a myth. In modern cosmology there is no such event because there's no way to adduce such an event. Its based on an extrapolation. There are a lot of myths in pop physics. This one is explained in Peebles text on cosmology. Would you like me to quote that passage of his text?
I havent read anyting knowingly by Peebles, a quick google flags up dozens of articles and papers by him. Where would you suggest I start.
I have understood the original concept of Big Bang from a singularity proposed by LeMaitre was a myth, although it is still taught as fact by some. The inflationary models put forward by Guth and Linde were big improvements, and explained a lot. None of the inflationary models preclude a hot expansion stage of the universe. Which is what I am probably naively assuming is what people are referring to as the Big Bang today.
What I dont grasp is the multiverse idea. I can grasp the idea of Aeons put forward by Penrose, but find multiverses a little like singularities in the original Big Bang(LeMaitre) hard to believe.
If I am reading you correctly, extrapolating backwards an event can not be defined without evidence. Is the CMBR no longer considered as evidence for a hot expansion stage of the universe, ie a version of Big Bang? Are you referring to another theory I dont know anything about yet?
I am interested in anything you have to say, so if it is no bother if you have the Peebles text on Cosmology easily to hand, I would be interested to see what he has to say.
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I am interested in anything you have to say, so if it is no bother if you have the Peebles text on Cosmology easily to hand, I would be interested to see what he has to say.
From Principles of Physical Cosmology by Peebles, page 6
The familiar name for this picture, the "big bang" cosmological model, is unfortunate because it suggests we are identifying an event that triggered the expansion of the universe, and it may suggest the event was an explosion in space. Both are wrong. ... If there were an instant, at a "big bang," when our universe started expanding, it is not in the cosmology as ow accepted, because no one has thought of a way to adduce objective physical evidence that such an event occurred.
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I am interested in anything you have to say, so if it is no bother if you have the Peebles text on Cosmology easily to hand, I would be interested to see what he has to say.
From Principles of Physical Cosmology by Peebles, page 6
The familiar name for this picture, the "big bang" cosmological model, is unfortunate because it suggests we are identifying an event that triggered the expansion of the universe, and it may suggest the event was an explosion in space. Both are wrong. ... If there were an instant, at a "big bang," when our universe started expanding, it is not in the cosmology as now accepted, because no one has thought of a way to adduce objective physical evidence that such an event occurred.
Thankyou very much for that ?
As I understand it, the inflationary stage of space came first which caused the production of matter from virtual particles, a bit like hawking radiation around a black hole, (other possible mechanisms also exist). Do you have one or more preferred models for particle creation during the inflationary stage of the current universe?
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As I understand it, the inflationary stage of space came first which caused the production of matter from virtual particles, a bit like hawking radiation around a black hole, (other possible mechanisms also exist). Do you have one or more preferred models for particle creation during the inflationary stage of the current universe?
No. Sorry but I don't know much about quantum cosmology. I've only studied the dynamics of cosmological models.
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Peebles seems to subscribe to the “hot big bang model. Page 7:
Thus the word “standard” is meant to express the fact that there is a very significant body of evidence indicating that the hot big bang model is a useful approximation of the real world.”
This book is over 25 years old. There will have been much progress in the field in that time, so it looks as though this model is surviving well.
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An event is something that occurs at a point in space time.
I have no problem with this, as long as we take into consideration the fact that a point is defined as having no dimensions/extent; but an event has finite extent. Given that caveat, your definition of an event seems quite workable.
https://en.wikipedia.org/wiki/Event_(relativity)
Strictly speaking, the notion of an event is an idealization, in the sense that it specifies a definite time and place, whereas any actual event is bound to have a finite extent, both in time and in space.
Let’s go with that.
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Is an observer aware of any events without light (detectable em radiation)?
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Is an observer aware of any events without light (detectable em radiation)?
How about walking into a wall, in the dark? That's an event you might be painfully aware of.
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Is an observer aware of any events without light (detectable em radiation)?
How about walking into a wall, in the dark? That's an event you might be painfully aware of.
Just because it is dark doesn't mean there is no em radiation ,does it?
Is low or high frequency em radiation the same as low or high frequency "light" ?
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An event is not defined to require anything to happen there. Most events happen in simply empty space. Recall that an event is a point in spacetime and that does not require anything to be present at the position r for the event (r, t)
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Is an observer aware of any events without light (detectable em radiation)?
You're confusing the term observer with person. The observer could be a system of clocks and rods and detectors at the location at the time of the event. It may be a person but that's not necessary.
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You're confusing the term observer with person. The observer could be a system of clocks and rods and detectors at the location at the time of the event. It may be a person but that's not necessary.
If it is a person ,is the person to be regarded as simply an outrageously sophisticated piece of machinery?
If the person or team of people is collating results from a piece of measuring equipment is he/she/they " so to speak the mechanical observer of last resort"? (entirely dependent on em signals to do their work)
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You're confusing the term observer with person. The observer could be a system of clocks and rods and detectors at the location at the time of the event. It may be a person but that's not necessary.
If it is a person ,is the person to be regarded as simply an outrageously sophisticated piece of machinery?
If the person or team of people is collating results from a piece of measuring equipment is he/she/they " so to speak the mechanical observer of last resort"? (entirely dependent on em signals to do their work)
You're getting into metaphysics and semantics now.
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You're getting into metaphysics and semantics now.
That seems fair (metafluff :) )
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Coordinates are a means of locating an event. Multiple observations are possible for the same event, yet with different coordinates.
An event is a change of state of a system, simple or complex, as Colin2b mentioned in #1.
Perception by an observer or proxy (video), requires a messenger (photon).
If you contact an object, sensory input (touch) is mediated by radiation via the electron cloud surrounding each nucleus.
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An event is a change of state of a system, simple or complex, as Colin2b mentioned in #1.
Colin was wrong on that point. Don't get used to it since Colin rarely makes a boo boo. :)
Note that a car skidding to a stop allows observation of the event "car stopped" by locating the end of the skid mark which could have been located without light, e,g, the conductivity of the road mapped out would denote where it is.
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An event is a change of state of a system, simple or complex, as Colin2b mentioned in #1.
Colin was wrong on that point. Don't get used to it since Colin rarely makes a boo boo. :)
Note that a car skidding to a stop allows observation of the event "car stopped" by locating the end of the skid mark which could have been located without light, e,g, the conductivity of the road mapped out would denote where it is.
It would appear that @phyti is misquoting me!
I was answering this question from @geordief:
I understand that an "event" is used to mean a point on a spacetime coordinate system or it can be one element of the set of aĺl events (which doesn't help).
But if we take an event as a physical occurrence , what can we say about it?
Taking this physical occurrence I replied:
“We define what an event is. Usually it is when something happens and we can define the point at which it happens as a spacetime coordinate. “
I didn’t go into events on the manifold as I assumed that was what @geordief meant by the coordinate system.
I was also clear that we are talking about a point not a ‘smear’. The examples I gave “The happening can be anything, an object passing a point, changing speed, hitting something, emitting a photon, etc” did not all imply a change of state. For example, an object passing a point requires no change of state.
To emphasise what @PmbPhy is saying, the skid is not an event but a series of events starting with ‘brakes applied event’ and ending with ‘stops event’.
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goerdief;
"But if we take an event as a physical occurrence ,"
Colin2B;
"Usually it is when something happens"
happen=occur
myself;
An event is a change of state of a system, simple or complex,
'complex' allows for sequential or prolonged events, a process of any duration.
An object passing a point requires observation/perception, which requires light emission, which qualifies as a change of state. It's why the photon is referred to as the messenger particle. It effectively says, 'something happened over here'. People in the dark use an artificial light source.
If all photon production were to stop, awareness, consciousness, and life itself would cease.
The coordinates of any event are not the same as the event, no more than a picture of an object is the same as the object.
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goerdief;
"But if we take an event as a physical occurrence ,"
Colin2B;
"Usually it is when something happens"
happen=occur
You still misquoted me.
I said “usually” this does not imply always as you seem to have interpreted it.
Also, happen ≠ occur, the 2 are different.
myself;
An event is a change of state of a system
Occurrences do not require a change of state.
I was walking in some hills recently, limestone occurs there and has done for millions of years.
Write out a sequence of “1s” = 11111111111 look at the 3rd, 4th and 5th occurrence of 1. No change of state there!
The definition used by @PmbPhy is the correct one.
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I said it before and I'll said it again: An even is merely a point in spacetime. It does not require anything to be at the location of the even nor does it require anything to happen at that location. Empty space for a long period of time is a good example of spacetime.
The more you attempt to use a dictionary for this term the more trouble you'll have learning it. Please don't do that since it makes our job harder. And the harder it will take for you to learn the actual physics of anything in physics. And
I hate repeating myself.
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1905 paper, A. Einstein,
par.1, simultaneity
"If we wish to describe the motion of a material point, we give the values of its co-ordinates as functions of the time."
"We have to take into account that all our judgments in which time plays a part are always judgments of simultaneous events."
par. 3, transformation of coordinates
"To any system of values x, y, z, t, which completely defines the place and time of an event in the stationary system,"
[the coordinates are variables associated with an 'event', and the event is variation of position or 'motion' of a particle.]
[For accuracy, I prefer the original author of a publication. Wiki is correct some of the time]
Colin2B;
“Write out a sequence of “1s” = 11111111111 look at the 3rd, 4th and 5th occurrence of 1. No change of state there!”
[Not observing it in its current state, but the sequence changed as it was written. Now the total complex event is the transformation of a blank paper to one containing a sequence of 1’s, which required energy.]
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1905 paper, A. Einstein,
par.1, simultaneity
"If we wish to describe the motion of a material point, we give the values of its co-ordinates as functions of the time."
...
To describe motion means to give a worldline which means to state a sequence of point events.
The terminology of events and spacetime wasn't defined until a few years after that paper was published.
I really know what I'm talking about here. I have a small mountain of relativity texts which back me up by defining and using the term "event' as well as working with relativity for about 35 years
Please note that although an event need not have anything in the space its located in, it can still be used to describe s physical event.
I'm ending my contribution here and will only respond upon request, not if someone who keeps making the same mistakes.
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PmbPhy#60;
How can you assign a coordinate to empty space, i.e. without a reference object? Distance, time, and motion are only relative to a reference frame, in SR.
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From a Wiki page, july 2006:
"1. Relativity theory depends on reference frames. A reference frame is a point in space at rest, or in uniform motion, from which a position can be measured along 3 spatial axes. In addition, a reference frame has a clock moving with the reference frame, allowing the measurement of the time of events.
An event is an occurrence that can be assigned a single unique time and location in space relative to a reference frame: it is a "point" in spacetime."*
"2. Let's define the event to have space-time coordinates in system S and in S'."
[1. Events are physical occurrences, and measurements allow recording spatial position and time of events.]
[2. Is not defining 'event', but properties of an event for identification purposes. The coordinate transformations calculate the coordinates of the S' frame from the S frame.
S and S' observe the same event, but with different coordinates, therefore the coordinates cannot be the event. The spacetime point is an abstraction or figure of speech, just as a trajectory, orbit, etc., i.e. a perception with no physical reality outside the mind.]
* This sentence is ambiguous. "it" is not redefining 'event', but defining 'point' as corresponding to the coordinates of the event. Option 2 would be to call the sentence a contradiction of terms. The time coordinate is in reality, a simultaneous clock event.
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An event is an occurrence that can be assigned a single unique time and location in space relative to a reference frame: it is a "point" in spacetime."*
* This sentence is ambiguous. "it" is not redefining 'event', but defining 'point' as corresponding to the coordinates of the event.
It’s not at all ambiguous, it just conflicts with your own ideas.
The spacetime point is an abstraction or figure of speech, just as a trajectory, orbit, etc., i.e. a perception with no physical reality outside the mind.]
Try standing on an object’s trajectory and tell us whether the impact you feel is an abstaction.
@PmbPhy and @Halc are not going to repeat that your definitions are wrong, but that doesn’t make yours right.
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PmbPhy#60;
How can you assign a coordinate to empty space, i.e. without a reference object? Distance, time, and motion are only relative to a reference frame, in SR.
I don't think you can in practice. Typically a coordinate system is defined by using a reference. But that doesn't mean that space is filled with stuff.