Relativity of Simultaneity and wave/particle duality.

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Main Question or Discussion Point

Why is it that the relativity of simultaneity isn't used to explain wave/particle duality?

RoS requires that matter be in different places according to the speed of the observer. All observers are equally correct.

This would seem to require that particles posses a wave characteristic that allows them to exist anywhere throughout space-time.
 

Answers and Replies

  • #2
JesseM
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Why is it that the relativity of simultaneity isn't used to explain wave/particle duality?

RoS requires that matter be in different places according to the speed of the observer. All observers are equally correct.
Don't conflate "different coordinates" with "different places"! By analogy, if we have a 2D plane with different dots drawn on it, and then we place some transparent Cartesian coordinate grids on top of the 2D plane, then different choices about how to orient the x-y axes of our coordinate grids relative to the 2D plane will result in different possible values for the x-coordinate of a particular dot, but that doesn't mean the dot itself is existing at multiple positions on the plane or that it needs to have a wave-like characteristic.
 
  • #3
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JesseM...

Thanks for responding. I understand the analogy to the distinction between place and coordinates. On one level, it makes perfect sense and answers my question.

I'm still somewhat uncomfortable with it, though.

In your analogy, the dots are in the same place. Only the perspective changes. This would apply well to a 4 dimensional view of space-time.

However, when knocked down to the 3 dimensional experience of space-time to which we are limited, each observer in relative motion actually experiences the "dots" in different places. Ontologically speaking, the dots actually "exist" in different places.

Wouldn't that require that they exhibit the wave characteristic? When measured or decohering they appear to us as particles, but they must exist as waves?
 
  • #4
JesseM
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However, when knocked down to the 3 dimensional experience of space-time to which we are limited, each observer in relative motion actually experiences the "dots" in different places. Ontologically speaking, the dots actually "exist" in different places.
What do you mean by "experiences the dots in different places", though? Ideally, a spacetime coordinate system is constructed by a system of rulers and clocks, with each event assigned coordinates based on local readings of the ruler and clock that were next to it as it happened. Each observer uses a ruler and clock system at rest relative to themselves, and the same event can be next to different positions on each observer's ruler and different clocks showing different readings. On this thread I illustrated two such ruler/clock systems moving along next to each other, and included the following picture illustrating how regardless of which coordinate system you use to define simultaneity, everyone agrees on the local facts about which ruler and clock readings on different observers' systems line up with one another:

MatchingClocks.gif


Suppose a particular event occurs at the center of the circled region, like a firecracker going off. You can see that system A will assign the event a position of 346.2 meters and a time of 1 microsecond, while system B assigns it a position of 173.1 meters and a time of 0 microseconds. But is there any "ontological" disagreement here? I don't think so, they both agree that when the firecracker went off it was next to the 346.2-meter mark on ruler A and also next to the 173.1-meter mark on ruler B, and that the clock next to it on ruler A read 1 microsecond while the clock next to it on ruler B read 0 microseconds. There is no disagreement over these physical facts about what was going on in the local neighborhood of the firecracker explosion, it's just that frame A uses the readings on ruler/clock A to assign coordinate labels to that event, while frame B uses the readings on ruler/clock B to assign coordinate labels to the event. So it's really no different from the fact that if you laid two different transparent coordinate grids on a 2D plane, you might simultaneously see that a particular dot lined up with the x=5 line on the first grid and the x=7 line on the second grid.
 
  • #5
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I'm referring to what Greene calls a "now slice" and what Petkov calls "a 3 dimensional subset." Each slice/subset is as valid as all the others and none agree when in relative motion.

It's not a measurement issue. Greene calls it a "now list." What exists though all space time at a given instant. Observers in relative motion have different now lists.

In one observer's world, I haven't been born yet. In another, my grandson is being Bar Mitzvahed. They are both correct, as am I typing this with no grandson yet.

What this means is that each person’s experience of reality is reality, not an illusory effect. The net effect of this is that there are an infinite number of valid different realities contained in our universe.

When one looks at the wave aspect of matter, spread throughout ALL of space-time, it all of a sudden seems to make sense, given the above.
 
  • #6
JesseM
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I'm referring to what Greene calls a "now slice" and what Petkov calls "a 3 dimensional subset." Each slice/subset is as valid as all the others and none agree when in relative motion.
But that's fundamentally no different than a "same x-coordinate slice" through space.
josephwouk said:
It's not a measurement issue. Greene calls it a "now list." What exists though all space time at a given instant. Observers in relative motion have different now lists.
Why do you think it's "not a measurement issue"? It's simply the set of events assigned the same t-coordinate by each inertial frame.
josephwouk said:
In one observer's world, I haven't been born yet. In another, my grandson is being Bar Mitzvahed. They are both correct, as am I typing this with no grandson yet.
No, you're taking the whole thing way too metaphysically, it isn't about different observers having different "worlds", it's just about different inertial frames assigning t-coordinates differently. In fact the whole idea that I should call the inertial frame in which I am at rest "my frame" is purely a matter of human convention, there is nothing physical that compels me to use that coordinate system or to see it as "my" perspective. Similarly it's also common to use a convention where an observer is located at the spatial origin of their own coordinate system (x=0, y=0, z=0) but that doesn't mean that observers at rest relative to each other and at different positions are in different "worlds" because when they use these different spatial coordinate systems they disagree on the position coordinates of different objects and events.
 
  • #7
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Jesse, help me out here...

In our world there is no such thing as a "t coordinate" anymore than there is such "thing" as an equator. These are concepts we use to communicate with each other.

In the world there are actual things in actual relations with one another.

I do not consider that observation to be "metaphysical."

Why should it be illusory that what "exists" in your world at this instant is real? Why say the description (coordinates) is anything more than just words/ideas?
 
  • #8
JesseM
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Jesse, help me out here...

In our world there is no such thing as a "t coordinate" anymore than there is such "thing" as an equator. These are concepts we use to communicate with each other.

In the world there are actual things in actual relations with one another.
I don't really know how you define "actual things", this itself seems rather metaphysical. Is an electron an actual thing or is it just an abstract entity used in mathematical models which we use to make predictions about macroscopic events like instrument readings? If an electron is an actual thing, how about a wavefunction?

But the question more relevant to this discussion is: do you think Greene's "now list" is an actual thing? If events are deemed to happen at the "same time" in my frame that doesn't mean I see them at the same time with my eyes since light takes time to reach me, it's a much more abstract process where I might say something like "OK, in 2010 I saw the light from an event 10 light-years away according to my ruler, then in 2020 I saw the light from an event 20 light-years away according to my ruler, so I conclude that in my frame both events happened simultaneously in 2000". The only really concrete experience of the relative timing of events is when the light from different events reaches our eyes, all other conclusions about simultaneity would seem to fit your description of "concepts we use to communicate with each other".
josephwouk said:
Why should it be illusory that what "exists" in your world at this instant is real?
What does "your world at this instant" mean? Is it purely what I am seeing at this instant, or does it include some more abstract notion of events happening "now" that I can't actually learn about until much later? Why should I believe in any such objective truth about what is happening "now"? I'm not saying I should deny that there is an objective external reality beyond what I am experiencing at this local point in spacetime, but I am free to take the eternalist perspective that the objective external reality is everything throughout spacetime, rather than the presentist perspective that the objective reality is only what is happening in some objective "present moment". There seems no compelling reason to believe in any nonlocal notion of the "present" ('nonlocal' meaning that it goes beyond just what light rays are converging on my position as I am saying this) at all, saying that events at different locations happened "at the same time" (even though I didn't see them at the same local point in my own history) need not be anything more than a concept we use to communicate, like the equator.
 
Last edited:
  • #9
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Why is it that the relativity of simultaneity isn't used to explain wave/particle duality?

RoS requires that matter be in different places according to the speed of the observer. All observers are equally correct.

This would seem to require that particles posses a wave characteristic that allows them to exist anywhere throughout space-time.
I rather like this notion. Not exactly as stated, and for the same reasons that Jesse brought up.

You attempt to use it in order to answer why particles look like waves. So you've assumed particles as your choice of what is physically real, and try to see how they can look spread-out like waves.

You can try to take this the other way too and start with waves, or continuous fields, and ask how these could contrive to look quanta.
 

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