Is there an Instant in Time That's Everywhere The Present

[sb635]

Is there an Instant in Time That's Everywhere "The Present"

We sit in a room. I see you and you see me. We both understand we are seeing each other as we "were" a small time interval in the past. The speed of light is finite and the distance traveled by the light from me to you, and you to me, is nonzero, and it takes time for the light to travel. But does not this demand that the matter that makes you and I up was both physically present at this, say, "common instant of light reflecting from you and me"? Snap your fingers perfectly, an instantaneous snap. Is there so meting physically "going on" on the other side of the Earth then? I say yes, even if I am not observing it. On the moon? Yes. On the Sun? Yes. In a Galaxy billions of light years away? Yes. To me, everywhere at once, there is a physical instant in time that is "The Present."

 

[WannabeNewton]

There is no absolute notion of "the present"; special relativity got rid of that concept.

 

[king vitamin]

There is no problem with a global definition of simultaneity with respect to an inertial observer:

http://en.wikipedia.org/wiki/Einstein_synchronisation

However, there is no definition of simultaneity which allows all inertial observers to agree that two arbitrary spacetime events are simultaneous. If you say that two events at (spatially separated) points A and B are simultaneous, there exists an observer with the same synchronization convention who will disagree.

(Note: the above is true in the absence of gravity, I'm not enough of an expert in GR to know if there are pathological exceptions.)

 

[sb635]

If so, there would seem to me a chance that the physical existence of matter throughout the universe could somehow get "out of synch" from location to location. I can't see how this is possible. It seems logical to me, because I believe in physical existence beyond any relativistic observation, all matter must coexist at once in an absolute physical space. This "at once" we call "the present."

With regards to relativistic observations, consider the following. An n-body system of observers (bodies) is considered. One of the observers observes a nonzero relative velocity for one of the other observers (bodies). To me then, there must be some type of absolute physical motion. You can not have an observed nonzero relative motion without an absolute physical motion, which must have occurred, regardless of observations of it were taken or not. The reverse in not true. If each body in the system is never seeing any relative motion on the part of the other bodies, then the whole system maybe moving and none of n bodies "sees" this. But if any nonzero relative motion is observed, there must have been some type of physical change of motion/location involved. This is Einstein's "external world."

 

[WannabeNewton]

There is no external world. There is no absolute velocity. There simply is no absolute notion of simultaneity. There are tons of threads on this and resources throughout the internet which can help you come to terms with that.

 

[sb635]

Here is a quote by Einstein:

"The belief in an external world, independent of the perceiving subject, is the basis of all natural science."

He said this in refutation of quantum mechanics. If you examine Einstein's Equivalence Principle, it shows what Einstein was talking about. A man is floating in an elevator. He sees one of the walls of the elevator approach him. He has a radar gun, and the radar gun says one of the walls is approaching, due its observed Doppler shift. The man is a physicist, and knows that, well, he would get the same observation if the wall were not approaching him, but somehow he and his radar gun were approaching the wall. How could that be? Perhaps a big mass is actually outside the elevator, and pulling the man to the wall. The internal observations cannot tell. This is what Einstein meant by "independent of the perceiving subject." The perceiving subject is the man, with his radar gun for observing. He is observationally isolated from Einstein's "external world." But note, and this an important note, some type of physical motion occurred. That's the only way the radar records a Doppler shift. Some type of physical "external world" motion occurred. Perhaps there were rocket engines attached to the outer walls of the elevator which fired, and it was not gravity, but external inertial accelerations that produced the interior observations. But something physically, absolutely moved in Einstein's "external world."

 

[WannabeNewton]

Acceleration is on a completely different playing field from velocity. There is no such thing as absolute velocity; if you propose there is then how would you detect it using local experiments? Acceleration is of course absolute and can easily be detected using accelerometers carried by observers.

As for your Doppler shift statement, if a light source is at rest with respect to an inertial observer then trivially that observer detects no Doppler shift. However if the light source is moving with respect to some other inertial observer then this observer can certainly detect a Doppler shift. It is not absolute.

 

[ghwellsjr]

It seems logical to me, because I believe in physical existence beyond any relativistic observation, all matter must coexist at once in an absolute physical space. This "at once" we call "the present."

This was the common belief prior to Einstein. And it is an appealing concept. The only problem is that there is no way to identify this absolute physical state (or do you know something that the rest of us don't know?) Even if you believe it to be true, you will be hard pressed to build a scientific theory based on it, and since Einstein's theory of Special Relativity is entirely compatible with the notion that there really does exist an absolute physical state, you'd be well-advised to learn it and put your mind at ease.

 

[WannabeNewton]

...(or do you know something that the rest of us don't know?)

Dun dun duuuun :)

Mod note: Off-topic posts moved to: https://www.physicsforums.com/showthread.php?p=4468881

 

[Nugatory]

Snap your fingers perfectly, an instantaneous snap. Is there something physically "going on" on the other side of the Earth then?

By "then"' you mean "at that exact same time", do you not?

If so, here's a question for you: What does it mean to say that two events occurred "at the same time"? Imagine two people on opposite sides of the Earth snap their fingers. How could you convince me that they snapped their fingers at the same time?

That sounds easy: I sit down somewhere 10 light-seconds away from both finger snappers. If the light from both events reaches me at the same time (note that this is one event, namely "my eye was just hit by two flashes of light) we'll say that they both happened at the same time, and allowing for light travel time, that time was ten seconds ago.

But it turns out that other observers using the exact same procedure but moving relative to me will find those two finger snaps not to be simultaneous, and will find events to be simultaneous that I didn't. That is, there is no universal notion of "at the same time".

Google for "relativity of simultaneity" and pay particular attention to Einstein's train example that comes up when you do.

 

[sb635]

By "then"' you mean "at that exact same time", do you not?

Yes.

If so, here's a question for you: What does it mean to say that two events occurred "at the same time"? Imagine two people on opposite sides of the Earth snap their fingers. How could you convince me that they snapped their fingers at the same time?

I assume you mean the two people on opposite sides of the Earth physically snapped their fingers at the exact same time in your mind's eye, as I immediately thought also from your words? If that actually happened as you and I envision, then me trying to convince you of that physical fact seems irrelevant to me, in terms of whether or not it did or did not happen simultaneously. I think both you and I are here envisioning the physical fact is that the snaps were simultaneous in our mind's eyes. Then this is the assumed external world physical truth to me. The snaps were absolutely simultaneous. They can be, can't they? After all, we are discussing physical events which are assumed to have occurred in a physical world, even if not observed.

Let's say two flashes of light occur at different times, according to at least one observer. Other observers see only a single flash. Were the flashes actually, physically simultaneous? One thing can be sure, at least one physical flash occurred. I next believe if a physical flash must have occurred, in the actual physical space where this happened, either it happened alone or another flash occurred in the same physical space, perhaps at a different absolute location, possibly even at the exact same physical absolute instant in time, or perhaps not. Any and all observations of events cannot tell internally if there were actual, physical singular or multiple flashes You can be guaranteed of one physical fact, though: at least one physical flash occurred. There is necessarily needed to me, a belief in Einstein's external, independent world, to even accept at least one physical flash physically occurred, "independent of the perceiving subject."

This is a common character I see with all thought experiments on these topics. There is no way to set one up without resolving the paradoxes, which are in fact resolved by the assumed physical setup. For example, the Twin Paradox. The setup words say one of the twins actually moved. The setup words resolve the paradox: It is the twin that moved which time dilated.

That sounds easy: I sit down somewhere 10 light-seconds away from both finger snappers. If the light from both events reaches me at the same time (note that this is one event, namely "my eye was just hit by two flashes of light) we'll say that they both happened at the same time, and allowing for light travel time, that time was ten seconds ago.

Your words tell me to take my point of view outside the scene and "look down," as I am sure you also did (by "seeing" yourself sit there in your mind's eye). To me, you and I are then "envisioning" in the "external world." In this "external world", I'll assume you mean the finger snaps occurred simultaneously. If that is the physical truth, then that's the physical truth in Einstein's "external world." If every observer actually knew the absolute physical truth, which is in my opinion, necessarily needed to believe in, to accept relative concepts, each could actually compute if they were in fact "faked out" about the timing of a truly, physically simultaneous event.

 

[ghwellsjr]

sb635, the question is: are you interested in learning Special Relativity?

 

[Nugatory]

Let's say two flashes of light occur at different times, according to at least one observer. Other observers see only a single flash. Were the flashes actually, physically simultaneous?

That's an interesting question, but I don't know how anyone can answer it without knowing what you mean by "simultaneous". Can you provide a definition of "simultaneous" and "at the same time" that will work for two observers who can see both flashes, or both finger-snappers? This is harder than it sounds; if you haven't already tried googling for "relativity of simultaneity", you should.

(We had been talking about two people in different places snapping their fingers. Now you're talking about flashes of light; I assume that you mean that the flashes are emitted from different places, both because that's your original question and because there's no problem deciding whether events at the same place happened at the same time).

 

[PeterDonis]

I think both you and I are here envisioning the physical fact is that the snaps were simultaneous in our mind's eyes. Then this is the assumed external world physical truth to me.

Nugatory didn't say both snaps were simultaneous. He just said to imagine that there are two snaps. He didn't say anything about their time relationship. That's the point: if all you know is that two snaps occurred, how do you tell whether or not they were "absolutely simultaneous"? What evidence would you look for?

The snaps were absolutely simultaneous. They can be, can't they?

No. Simultaneity is relative.

After all, we are discussing physical events which are assumed to have occurred in a physical world, even if not observed.

Yes, but that's a separate question from the question under discussion. Nobody is disputing that there is a physical world that exists independently of our observations. All we are saying is that that physical world that exists independently of our observations does not include "absolute simultaneity" as one of its features.

Let's say two flashes of light occur at different times, according to at least one observer. Other observers see only a single flash.

What keeps the other observers from seeing the second flash?

One thing can be sure, at least one physical flash occurred.

Why only one? You said at least one observer sees two flashes. Doesn't that mean at least two flashes must have occurred, even if other observers don't observe the second one? Didn't you say the physical world exists independently of our observations?

I next believe if a physical flash must have occurred, in the actual physical space where this happened, either it happened alone or another flash occurred in the same physical space, perhaps at a different absolute location, possibly even at the exact same physical absolute instant in time, or perhaps not.

You are assuming a lot here, though you probably don't realize it. You are assuming that there is an "actual physical space" (as opposed to an actual physical *spacetime*), in which there are "absolute locations", and that there are "absolute instants" of time. All of these assumptions are false. I know they seem obvious to you, but they're still false. If you want to understand how relativity works, you have to drop these assumptions.

This is a common character I see with all thought experiments on these topics. There is no way to set one up without resolving the paradoxes, which are in fact resolved by the assumed physical setup. For example, the Twin Paradox. The setup words say one of the twins actually moved. The setup words resolve the paradox: It is the twin that moved which time dilated.

The twin paradox can be stated without saying anything about which twin "moved". I'll agree that plenty of statements of the paradox aren't made as carefully as they should be, since they invite you to make assumptions that don't hold (such as the assumption that there is an absolute fact of the matter about which twin "moved"). Although in some cases, the paradoxes are stated that way on purpose, to see whether you are capable of questioning those assumptions.

In this "external world", I'll assume you mean the finger snaps occurred simultaneously.

Read what he said again, carefully. He made no such statement, and you are making an unwarranted assumption.

 

[sb635]

Yes, but that's a separate question from the question under discussion. Nobody is disputing that there is a physical world that exists independently of our observations. All we are saying is that that physical world that exists independently of our observations does not include "absolute simultaneity" as one of its features.

Are you saying in this external physical world independent of observations, that truly physically simultaneous events somehow can not occur? If you believe in the existence of a physical world independent of our observations, where to me that means events actually do physically happen regardless of being or not being observed, why can't there be two exactly simultaneous events in this physical world, and who cares about if they were observed or not, in terms of whether or not they physically occurred simultaneously?

What keeps the other observers from seeing the second flash?

Because of their type of absolute motion in the absolute world in which at least one flash occurred. Because of their motion they see the second flash apparently happen, if it did actually happen, at the same point of/in their dilated time.

Why only one? You said at least one observer sees two flashes. Doesn't that mean at least two flashes must have occurred, even if other observers don't observe the second one? Didn't you say the physical world exists independently of our observations?

Because if at least one flash was seen, there was, absolutely, at least one physical flash in the external, physical world. This fact, that there was at least one physical flash, is directly dependent on at least one relative observation seeing at least one flash. But the reverse is not true. If no observer sees a flash, this does not guarantee that no physical flashes ever occurred. But just one relatively observed flash occurring demands at least one physical flash. And if that's so, then where did it occur? It had to be at some absolute physical location in space at some just as absolute instant in time, if it was an actual physical event independent of observation.


There may have been more than one flash physically occur, and relative observations can't tell, and will never be able to resolve what is the "absolute truth of the external world." But even if just one flash was observed, there is one absolute thing which can be said: At least one flash physically happened. And the only type of "world" in which events do physically happen is an absolutely physical world, independent of observations, as Einstein stated. And then I think this physical world must be the same physical world for you, for me, for all physical matter existing at the same absolute instant in time that we call "the present."

To me, the entire concept of motion requires one to accept physical matter absolutely moves from some absolute location in space to some other absolute location in space over some absolute time interval. Motion to me, has to be in fundamental essence, truly absolutely physical. How an observer "sees" that motion progress through time is entirely a function of the observer's physical motion relative to the absolute space time with which this physical motion took place. Motion is physical. How we see it is relative.

You are assuming a lot here, though you probably don't realize it. You are assuming that there is an "actual physical space" (as opposed to an actual physical *space time*), in which there are "absolute locations", and that there are "absolute instants" of time. All of these assumptions are false. I know they seem obvious to you, but they're still false. If you want to understand how relativity works, you have to drop these assumptions.

This sounds in contradiction to your previous statement that you believe in an external physical world independent of observations. One can take such a point of view and still completely understand all of relativity. Like I said, the Equivalence Principle demands one accept the existence of a physical, external would "out side of the elevator," as Einstein clearly thought, per the quote I gave. If it didn't, there would not be a way to define what is meant by "inside of the elevator."

 

[mikiel]

I am conflicted about the nature of a thought experiment. I propose one in which I (its creator) say, A bomb goes off in Earth's atmosphere *at the same time* that a solar flare erupts from the Sun. Doesn't that establish the simultaneity of the events, i.e., that we can all imagine those events happening at the same time, regardless of what different frames of reference might see, i.e., seeing them happen at different times? And certainly they could happen at the same time in this physical solar system, regardless of who might see them happen at different times because of different frames of reference.
An observer midway between Earth and Sun would see them as the thought experiment dictated... happening simultaneously. No doubt an observer closer to Earth would see the bomb explode first and the flare later. But how could that alter the physical simultaneity of the events, happening at the same time as specified, regardless of when different points of view might see them?

 

[Dale]

A bomb goes off in Earth's atmosphere *at the same time* that a solar flare erupts from the Sun.

In which frame? The words "at the same time" don't mean anything unless you specify the reference frame.

No doubt an observer closer to Earth would see the bomb explode first and the flare later. But how could that alter the physical simultaneity of the events, happening at the same time as specified, regardless of when different points of view might see them?

Relativity isn't about optical effects. It is what remains after accounting for optical effects. An observer closer to the Earth would receive the light from the events, correct for the distance, and determine that they happened at the same time even though he received the light at different times (assuming that they were simultaneous in his frame).

 

[PeterDonis]

Are you saying in this external physical world independent of observations, that truly physically simultaneous events somehow can not occur?

Yes, because the concept of "truly physically simultaneous events" has no physical meaning.

If you believe in the existence of a physical world independent of our observations, where to me that means events actually do physically happen regardless of being or not being observed

Agreed, no argument here.

why can't there be two exactly simultaneous events in this physical world

Because the actual physical world doesn't work that way. I know your intuition says it ought to, but it doesn't. That's just the fact.

To be clear: there can be pairs of events in the actual physical world that are simultaneous to a particular observer; but there can't be pairs of events in the actual physical world that are "truly" simultaneous, in any absolute sense. Simultaneity is relative.

Because of their type of absolute motion in the absolute world in which at least one flash occurred.

There is no such thing as "absolute motion" in the "absolute world" (by which I assume you mean the actual physical world that exists independent of our observations). The actual physical world just doesn't work that way, even though your intuition says it ought to. There is only relative motion--motion of one object relative to another.

I think this physical world must be the same physical world for you, for me, for all physical matter

Yes.

existing at the same absolute instant in time that we call "the present."

No. There is no such thing as an absolute instant of time, whether it's the present or any other. The actual physical world doesn't work that way, even though your intuition says it ought to.

To me, the entire concept of motion requires one to accept physical matter absolutely moves from some absolute location in space to some other absolute location in space over some absolute time interval.

Yes, I understand that this is how it seems to you. But how it seems to you is not how it is; that's what relativity tells us. If you want to understand relativity, you will need to change your concept of motion.

Motion is physical. How we see it is relative.

It's true that there is something absolute about an object in spacetime: it has a worldline, a curve in spacetime that it follows, and that worldline is independent of how any particular observer sees it. But there is no absolute sense in which the object is "moving" or "not moving"; it just has a worldline.

This sounds in contradiction to your previous statement that you believe in an external physical world independent of observations.

That's because your concept of "an actual physical world independent of observations" attributes properties to that actual physical world that it doesn't actually have. Saying that the actual physical world exists independently of our observations is not the same as saying there is absolute space, absolute time, or absolute motion. If you think it is, then your concept of the actual physical world is wrong, and you will need to change it if you want to understand relativity.

 

[TheBC]

There is no external world.

Dalespam told me there are no solipsists on this forum?

Nobody is disputing that there is a physical world that exists independently of our observations.

If that is the case, and spacelike events, simultaneous with my 'now' event, exist out there, and simultaneity is relative, then 4D spacetime is the physical observer independent 'world' out there.

 

[Nugatory]

Are you saying in this external physical world independent of observations, that truly physically simultaneous events somehow can not occur?

We've suggested several time already that you google for "Relativity of simultaneity" and Einstein's thought experiment that goes with it. Have you done this?

I don't think so, or you wouldn't still be talking about "truly physically simultaneous events"... You'd either be saying "OK, now I understand" or you'd be asking follow-up questions about how the relativity of simultaneity argument works.

This is not strange weird controversial out-on-the-edge stuff that we're talking about. It was discovered more than a century ago, it has been a basic part of a first-year physics curriculum for many decades, and there is no shortage of experimental evidence to confirm special relativity. Not studying it, yet asking questions about "an instant in time", makes about as much sense as trying to design a jetliner but refusing to look at any technology developed since the 19th century.

So, one more time, as I said back in post #10 of this thread... Google for "relativity of simultaneity" and pay particular attention to Einstein's train example that comes up when you do.

 

[PeterDonis]

If that is the case, and spacelike events, simultaneous with my 'now' event, exist out there, and simultaneity is relative, then 4D spacetime is the physical observer independent 'world' out there.

This is one possible viewpoint, yes, and it's the most natural one to take once you understand SR. But it's worth bearing in mind that we do not *know* that particular events spacelike separated from us "exist". For example, we do not know exactly what events are taking place in the Andromeda galaxy "right now", i.e., spacelike separated from us here on Earth.

We can extrapolate from the last data we have from the Andromeda galaxy, based on the light we are just now receiving from it; but that's an extrapolation, and it might be wrong, not just because we can't do perfect extrapolation, but because our data is incomplete. The only actual data we have is from our past light cone, and there are lots of events in the past light cone of the Andromeda galaxy (and which can therefore causally affect what happens in the Andromeda galaxy) that are not in our past light cone.

Any model we build of 4-D spacetime will suffer from this same limitation. As a model, yes, the 4-D spacetime functions as the objective physical world that is there independently of our observations of it. But our knowledge of what events actually take place in that 4-D spacetime is always limited.

 

[sb635]

We've suggested several time already that you google for "Relativity of simultaneity" and Einstein's thought experiment that goes with it. Have you done this?

So, one more time, as I said back in post #10 of this thread... Google for "relativity of simultaneity" and pay particular attention to Einstein's train example that comes up when you do.

Yes, I've read tons on relativity theory on the net, and have read and studied many relativitic texts books. I've published one paper on numerical general relativity. The link is at

http://sb635.qwestoffice.net/all_pages.pdf

 

[ghwellsjr]

One can take such a point of view and still completely understand all of relativity.

Are you one?

 

[Nugatory]

Yes, I've read tons on relativity theory on the net, and have read and studied many relativitic texts books.

So do you agree with the notion of relativity of simultaneity in special relativity or not?

And if you don't, what is the error you find in the two standard ways of approaching RoS?
1) Einstein's train experiment, which provides a coordinate-free demonstration that observers in motion relative to each will disagree about the simultaneity of pairs of events, even when using one of the most physically reasonable definitions of when an event occurred.
2) The Lorentz transformations, which show that observers in motion relative to one another will in general assign different time coordinates to events.

 

[Dale]

Dalespam told me there are no solipsists on this forum?

Maybe instead of assuming from one quote that you know WBN's position you should ask him instead.

 

[Adrian07]

Going back to the first 2 posts, if things don't happen simultaneously on Earth how can we have accurate timetables for things like airlines and if a person in LA agrees to talk to someone in London at a specific time GMT how can they both be ready to talk at the specified time if its not simultaneous otherwise one of you would miss the call. The problem lays with the finite speed of information and observers in different reference frames receiving that information at different times.

 

[Dale]

if things don't happen simultaneously on Earth how can we have accurate timetables for things like airlines and if a person in LA agrees to talk to someone in London at a specific time GMT how can they both be ready to talk at the specified time if its not simultaneous otherwise one of you would miss the call.

Things don't happen simultaneously in an absolute sense. Simultaneity is a convention, not a physical fact. Once you adopt a convention, like UTC, then by that convention simultaneity can happen. The things you mention work because we have adopted a global time convention, but it is just a convention and nothing physically mandates the use of UTC.

 

[PeterDonis]

The problem lays with the finite speed of information and observers in different reference frames receiving that information at different times.

And the reason that adopting a common standard of simultaneity for everybody on Earth works, in a practical sense, is that the relative velocity between any two people on Earth is very small compared to the speed of light, and the light-speed travel time between any two points on Earth is very small compared to the time scale of our actions.

So relativistic effects for everyday objects and actions on Earth are very small and we can ignore them in everyday life. But with accurate enough measurements we can certainly detect them.

 

[mikiel]

Quote by sb635 View Post

If you believe in the existence of a physical world independent of our observations, where to me that means events actually do physically happen regardless of being or not being observed

PeterDonis;

Agreed, no argument here."
...

Saying that the actual physical world exists independently of our observations is not the same as saying there is absolute space, absolute time, or absolute motion.

Even disregarding absolutes, I think sb635 is saying that the physical world and its events happen independent of when they are observed. I agree. As in my example above, if in “a physical world independent of our observations” a flare on the sun and a bomb on Earth go off at the same time, even when/if different observers in different frames see that happen at different times, it does not change the simultaneity of the events “independent of observations.”

That is also my answer to DaleSpam’s reply above:

In which frame? The words "at the same time" don't mean anything unless you specify the reference frame.

Frame of reference is irrelevant to when event happen if the world and its events are “ independent of our observations,” as PeterDonis agreed above.

Quote by sb635 View Post (my bold);

why can't there be two exactly simultaneous events in this physical world...?

PeterDonis:

“Because the actual physical world doesn't work that way. I know your intuition says it ought to, but it doesn't. That's just the fact.

That didn’t answer the question. It just says ...’because there can’t be...’

PeterDonis:

To be clear: there can be pairs of events in the actual physical world that are simultaneous to a particular observer

But if you agree that the world and its events exist independent of observation, then observation does not determine when events happen.

Btw, I too have studied the relativity of simultaneity, but understanding that argument does not require agreement with it... especially given the agreed fact that the physical world and its events exist and happen independently of observation from various frames of reference, as this discussion is showing.

 

[PeterDonis]

Even disregarding absolutes, I think sb635 is saying that the physical world and its events happen independent of when they are observed. I agree.

So do I, but that doesn't mean what you think it means. See below.

As in my example above, if in “a physical world independent of our observations” a flare on the sun and a bomb on Earth go off at the same time

You are assuming that "at the same time" has an absolute meaning, independent of observers. If you're going to use a scenario to argue for your interpretation, you can't just assume it at the outset.

The correct way to state this would be "in a physical world independent of our observations, there are two events: a flare going off on the Sun, and a bomb going off on the Earth". Then, in order to actually make predictions, you would have to specify things like the causal relationship of those two events: are they timelike separated, null separated, or spacelike separated? But you can specify everything you need to specify about those two events in order to make predictions, without ever even asking the question "do these two events happen at the same time?", much less committing to a single absolute answer to it.

even when/if different observers in different frames see that happen at different times, it does not change the simultaneity of the events “independent of observations.”

You're assuming that there is a simultaneity of the events independent of observations. There isn't; the concept doesn't even have any meaning. See above.

Frame of reference is irrelevant to when event happen if the world and its events are “ independent of our observations,” as PeterDonis agreed above.

Yes, but again, that doesn't mean what you think it means.

But if you agree that the world and its events exist independent of observation, then observation does not determine when events happen.

No. But you think that's because "when events happen" has some absolute meaning, and I think it's because "when events happen" has *no* absolute meaning; it's a feature of our models of reality, not of reality itself.

Btw, I too have studied the relativity of simultaneity, but understanding that argument does not require agreement with it...

Do you agree with all of the experimental results that are predicted by relativity? If you do, but you disagree with relativity's standard explanation of those results, then you need to come up with your own theory that also makes all of those predictions, but doesn't include relativity of simultaneity, and does include some kind of absolute "when things happen". Good luck.

If you don't agree with the experimental results, what do you think is wrong with them?

 

[mikiel]

Frame of reference is irrelevant to when events happen if the world and its events are “independent of our observations,”

According to relativity, are they or are they not independent of observation? ("Not" is the answer according to the relativity of simultaneity, RoS.)

Again, “if you agree that the world and its events exist independent of observation, then observation does not determine when events happen.” This is basic logic, but it contradicts RoS.

Finally, you seem to agree that, as I said, "... the physical world and its events exist and happen independently of observation from various frames of reference,... “

Sorry for the repetition, but either things happen independent of when they are observed or observation determines when things happen, and there is no world independent of observation. It can not be both ways.

 

[Nugatory]

Going back to the first 2 posts, if things don't happen simultaneously on Earth how can we have accurate timetables for things like airlines and if a person in LA agrees to talk to someone in London at a specific time GMT how can they both be ready to talk at the specified time if its not simultaneous otherwise one of you would miss the call. The problem lays with the finite speed of information and observers in different reference frames receiving that information at different times.

Careful - no one is saying that "things don't happen simultaneously on earth". We're saying that events that are simultaneous to us people on earth, all of whom are for practical purposes at rest relative to one another, are not simultaneous to the entire universe, most of which is not at rest relative to us.

Neither accurate timetables nor agreeing to talk by telephone between LA and London require any notion of absolute simultaneity, although for different reasons.

Timetables: When the timetable says "Flight 1108 will take off from New York at noon EST and will land in Lima Peru at 8:00 PM EST" (I piked those cities because they're in the time zone to simplify things), it's saying that the plane will take from New York when the clocks in New York read noon , and it will land in Lima when the clocks in New York read 8:00 PM. It's not saying anything about what's happening in New York "at the same time" that the plane lands in Lima, nor what's happening in Lima "at the same time" that the the plane takes off from New York.
I do agree that we expect (for many good and convincing reasons, not least of which is that we can pick up a telephone, call the other city and ask) that the when the clocks in Lima read 8:00 PM the clocks in New York also will. However, that only works because at rest relative to the people in the other city, because...

Telephone: The events at the two ends of the phone conversation are never simultaneous for any observer anywhere. They are always separated by the speed of light delay for the signal to pass through the wires, about 20 milliseconds for the conversationalists at rest on the surface of the earth. Thus, when Lima asks New York "My clock read 8:00 PM; what time does your clock read?", he'll get back the answer "8:00 PM" 40 milliseconds later.

 

[phinds]

Frame of reference is irrelevant to when events happen if the world and its events are “independent of our observations,”

According to relativity, are they or are they not independent of observation? ("Not" is the answer according to the relativity of simultaneity, RoS.)

Again, “if you agree that the world and its events exist independent of observation, then observation does not determine when events happen.” This is basic logic, but it contradicts RoS.

Finally, you seem to agree that, as I said, "... the physical world and its events exist and happen independently of observation from various frames of reference,... “

Sorry for the repetition, but either things happen independent of when they are observed or observation determines when things happen, and there is no world independent of observation. It can not be both ways.

You misunderstand the relativity of simultaneity. Things do happen independent of observation but WHEN they happen is observer dependent. If a bomb goes off on the moon and a solar flare happens, all observers will agree that they happened, and unless you want to get into interpretations of QM, all will agree that they happened whether or not anyone was watching. BUT, as to which one happened "first", that will be observer dependent. It is meaningless to say "they happened at the same time". PeterDonis has already explained all of this. Do you not understand what is being said or do you not agree with it?

 

[PeterDonis]

Frame of reference is irrelevant to when events happen if the world and its events are “independent of our observations,”

You keep on assuming that events existing independent of our observations *requires* that there is an absolute fact of the matter about when events happen. You can't make that assumption. If you want to try to prove it, you're going to have to, as I said before, produce a theory that reproduces all of the experimental predictions of SR, but also assigns an absolute "when" to each event that is independent of frames of reference. Can you do that? If not, you can't help yourself to the assumption that "when" events happen is absolute.

According to relativity, are they or are they not independent of observation? ("Not" is the answer according to the relativity of simultaneity, RoS.)

Incorrect. Relativity of simultaneity is a completely different question from whether or not events exist independently of observation. See above.

Again, “if you agree that the world and its events exist independent of observation, then observation does not determine when events happen.” This is basic logic

It's also irrelevant to what you're trying to prove. You're correct that observation does not determine when things happen; this is because "when things happen" has no absolute meaning at all. Of course observation isn't going to determine something that has no absolute meaning anyway.

Finally, you seem to agree that, as I said, "... the physical world and its events exist and happen independently of observation from various frames of reference,... “

Sure, I agree to that as you've stated it here, because it doesn't make any assumption about "when" things happen. But you can't draw any conclusions from this about "when" things happen, or whether or not "when" things happen has an absolute meaning. If you want to make any assertions about that, you're going to first have to establish them independently of any claims about the physical world existing independently of observations. See above.

Sorry for the repetition, but either things happen independent of when they are observed or observation determines when things happen, and there is no world independent of observation. It can not be both ways.

Your logic is flawed here. Things do happen independently of when they are observed; observation does not determine when things happen. But also, there is no absolute fact of the matter about when things happen. That's because "when" an event happens is simply not a feature of reality at all; events have no "when" in any absolute sense.

 

[PeterDonis]

When the timetable says "Flight 1108 will take off from New York at noon EST and will land in Lima Peru at 8:00 PM EST" (I piked those cities because they're in the time zone to simplify things), it's saying that the plane will take from New York when the clocks in New York read noon , and it will land in Lima when the clocks in New York read 8:00 PM. It's not saying anything about what's happening in New York "at the same time" that the plane lands in Lima

As you've stated it, that's not true, because you said clocks in New York reading 8 PM happens at the same time the plane lands in Lima. Which illustrates once again how careful one has to be with this stuff.

I do agree that we expect (for many good and convincing reasons, not least of which is that we can pick up a telephone, call the other city and ask) that the when the clocks in Lima read 8:00 PM the clocks in New York also will.

Actually, this is only true in the Northern Hemisphere winter, because Peru doesn't make DST adjustments, at least not according to timeanddate.com.

However, that only works because at rest relative to the people in the other city

Someone at rest in Lima won't be at rest relative to someone at rest in New York, because they're at different latitudes: New York is at about 40 degrees North, Lima is at about 12 degrees South. The velocity of someone at rest on the Earth's surface, relative to an inertial frame comoving with the Earth's center, is about 450 m/s times the cosine of the latitude, which works out to about 440 m/s for Lima and 345 m/s for New York. So the relative velocity of the two is about 95 m/s.

Of course the relativistic effect of this velocity is negligible in everyday terms, but it would be measurable with atomic clocks (order v^2/c^2 or about 1 part in 10^13; atomic clocks, I believe, are accurate to about 1 part in 10^14). The point is merely to reinforce that simultaneity is relative, and any practical definition of simultaneity that is used by people everywhere on Earth relies on the fact that the relativistic effects of their relative motion are negligible; it is not in any way a claim that everyone on Earth is actually at rest relative to each other.

The events at the two ends of the phone conversation are never simultaneous for any observer anywhere. They are always separated by the speed of light delay for the signal to pass through the wires, about 20 milliseconds for the conversationalists at rest on the surface of the earth.

Yes, this is true, and it's good to note that any talk about "simultaneity" really applies only to spacelike separated events, whereas the events at the two ends of the phone conversation are never spacelike separated; at best they're null separated (and signals traveling over wires go slower than the speed of light in vacuum, so in real life the events would be timelike separated).

 

[Dale]

This thread has already resulted in a spin-off, two bans, and some other infractions. It is time to close it down.