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Message: <blockquote data-quote="freyar" data-source="post: 6547327" data-attributes="member: 40227">I'll start by mentioning that I agree with Umbran's answers to your questions, but I'll throw in my 2 cents as well.There are a couple of levels of scientific theory here, and I think it's important to clarify in this case.  What we call the "theory of relativity" (whether you're talking about special relativity or general relativity) and "quantum mechanics" are basically mathematical frameworks that underlie more specific theories.  So, when I go teach quantum mechanics, I am teaching a set of axioms and mathematical tools and how they are used in specific theories.  For example, the framework quantum mechanics is used in, for example, the BCS theory of superconductivity or models of atomic & molecular physics or beyond.  Similarly, the basic framework of general relativity can be used in Einstein's general relativity but also carries over to many slightly modified formulations of gravity.  We tend to use the word "law" (as in "law of physics") for a specific concept or rule in physics --- basically one equation at a time.  "Law" tends to be used for the important ones; another similar word used in some cases is "theorem."  Regarding dark matter and dark energy, no, we don't know specifically what they are, but that's mostly a matter of specific theories.  For example, a majority of physicists who've looked at the evidence are quite sure that dark matter is a new type of fundamental particle, described within the framework of quantum mechanics and more specifically particle physics (quantum field theory).  The specific theory of those dark matter particles is unknown.  Dark energy is a little more interesting, in that we may only understand it when we understand a complete theory of quantum gravity (which we don't quite have a framework for at the moment).  But my feeling is that we likely understand what dark energy is (vacuum energy) but don't necessarily have a good handle on how to understand its value (though that's just a gut feeling).As Umbran mentioned above, events that can communicate with each other always stay in the same order.  So, since I can tell myself "ow, I've been shot in the leg," those two events stay in order.  Here's how I teach this in class: If two events happen at the same place relative to some person, they have a past-future ordering.  So, relative to me, getting shot and getting behind cover happen at the same place--- at me.  So they have order.  We should be precise for this case.  From my point of view, I'm at point A, and you're at point C shooting at me with a laser gun.  A tank is driving through and passes point B, which is on a direct line between you and me.  Now, if the tank and the laser pulse are both at point B simultaneously, everyone can agree I am not shot.  If they're not, there is a clock sitting at point B that can tell me if the laser pulse or the tank is at point B earlier.  BUT, the event of myself getting hit by the laser is somewhere else.  Someone flying around in a relativistic rocket ship might see the tank pass point B before or after I get shot depending on the precise circumstances.  And this all falls out of the math.I'll agree with Umbran's points about this and also say that you really have to be careful about saying things like "a single photon causing an interference pattern with itself."  If you measure the position of a single photon --- for example, send a single photon through a device and see where it hits a screen --- you will always get a single position.  The interference pattern shows up in the distribution of those positions if you repeat that single photon experiment many times.  Yes, each photon is interfering with itself, but a single measurement doesn't see the whole pattern.</blockquote>

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