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

[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.