So you’re saying that in these instances where we draw conclusions from a machine detecting something, that’s not really an observation?
I would be inclined to count a clock as doing just that.
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I don’t know if a clock observes what time looks like, but why is that a problem? Have we ever observed what gravity looks like? Or magnetism? Or… (insert a host of other physical phenomena)?
Clocks measure time. If that isn’t what they do, then what is it they do? The fact that they measure time rather strongly suggests that time is real - can you measure something that isn’t real?
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Right. Detecting a smell is not the same as seeing what the cause of the smell is.Correct me if I’m wrong, but in the case of time dilation, the equations are predicting a behavior that can be and has been detected in the amount of extra muons at ground level. However, what is in question is what is causing the effect of that particular behavior. This cannot be observed and therefore has to be subjectively inferred based on the relevant evidence.
Then I would say in that case there is a difference in how observation is being defined.
It’s not a problem. Those are examples of things that have to be subjectively inferred from evidence. Is there sufficient evidence for the existence of gravity? I would argue absolutely. But it is based on evidence, not because gravity itself has been observed.
What’s being measured are rates of change in relation to the past, present and future. That’s what we call time. Is it a real physical substance? Maybe. There is plenty of disagreement about it. Looking at the available evidence I’m not persuaded that it is. However, that doesn’t mean I’m necessarily right. The point is that it’s a subjective inference that requires looking at the evidence.
I don’t think that time is a ‘real physical substance’ any more than that gravity is a real physical substance. Perhaps we use the term differently but to me a substance is something composed of particles.
A rate of change is of course a change measured with respect to time. If not to time, than to what? What sort of evidence would convince you that something is really ‘time’ if it isn’t simply what clocks measure?
I can’t help feeling that you see a problem that doesn’t actually exist. Perhaps I misunderstand you and you are actually asking about the cause of time?
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If the claim is that the cause of the rates of the atomic clocks slowing down is the relativistic concept of time itself slowing down, then it seems to me that in order for time itself to have an effect on the clocks it would have to be some form of physical substance. How else would you explain it?
What do you understand by the term “physical substance”?
Physical substance usually refers to some type of atomic structure. But with time, if it is physical, I imagine it would have to be some kind of unknown physical substance. But I’m not the one saying that it’s physical. How else would you explain how time itself can have a physical effect on physical clocks?
If a physical substance is usually an atomic structure, but not always, what is it then?
I would ask you that since that is what seems to be implied by the claim that time itself can have a physically affect on physical objects. I’m not the one making the claim. I’m simply stating what it seems to imply. You’re welcome to illuminate me if there’s another way to look at it.
No, you’re the one making the claim that if time dilation is true, then time must be a “physical substance”. I’m not sure we’re using that term in the same way, because your claim doesn’t make sense to me. So I want to understand what you’re trying to say.
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I’m simply taking the claim of time itself causing clocks to slow down to what seems to be its logical conclusion. Is it not logical to conclude that a physical effect has a physical cause? If so, then somehow there must be something physical about time. And if it’s physical, it seems to follow that it would entail some kind of physical substance, would it not?
Maybe this will help clear things up a bit:
Aristotle and others (including, especially, Leibniz) have argued that time does not exist independently of the events that occur in time. This view is typically called either “Reductionism with Respect to Time” or “Relationism with Respect to Time,” since according to this view, all talk that appears to be about time can somehow be reduced to talk about temporal relations among things and events. The opposing view, normally referred to either as “Platonism with Respect to Time” or as “Substantivalism with Respect to Time” or as “Absolutism with Respect to Time,” has been defended by Plato, Newton, and others. On this view, time is like an empty container into which things and events may be placed; but it is a container that exists independently of what (if anything) is placed in it.
I don’t think that I’ve ever written the sentence along the lines of “time causes clocks to slow down”. That’s an odd way to phrase it, since to slow down presupposes the existence of time. It seems like a vacuous tautology to say that “time causes clocks to slow down (i.e. change less given a certain amount of time)”.
Ah, FINALLY you’re turning to mainstream philosophy of spacetime articles to express your viewpoints! Which view do you commit to? Aristotle or Plato?
Note that even for those who espouse the “substantivalist” (i.e. Platonic/Newtonian) view don’t regard time as a physical substance like water or sodium atoms. And I don’t think anyone has defended the argument that substantivalism is false because time is not a physical substance that can “cause” anything. It’s just not the right way to frame the dispute.
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Hmm. I’m trying to understand why clock rates change at different altitudes. If the claim that their measurements of the time that passes of objects traveling at speeds approaching that of light slows down because of time itself slowing down for those objects, that seems to be saying that the cause of the clock rates slowing down is time itself slowing down, does it not? If not, what is the explanation of why the rates of these clocks change at different altitudes?
Well, yes, the cause of (or perhaps better said: the reason for?) the clocks slowing down is that time itself slows down. Time is after all what the clocks measure. I don’t see why this is different than saying that the cause of a thermometer reading lower temperatures is that the temperature has gone down.
You stated that you don’t think time is a physical substance. So the question still remains. If the cause of clocks slowing down is time itself slowing down, and time is not a physical substance, how does something nonphysical produce a physical effect?
Through our physical senses we can empirically verify that changes in temperature actually happen. We cannot empirically verify that the concept of time itself changing speed can actually happen. It can only be subjectively inferred from available relevant evidence suggesting such to be the case.
I think we may be having a disagreement over phenomenon and interpretation of the cause of the phenomenon here. For a physicist, what defines a device as a clock is that it measures time, whatever time is. Many experiments have been done with clocks which show that subject to certain conditions, clocks slow down or speed up when subjected to different gravitational fields, as predicted by GR. In other words, time as measured by a clock is slowing down or speeding up depending on the gravitational field the clock is subject to. This statement, to me, is indisputable based on the scientific evidence, no matter what your philosophical interpretation of space and time is.
Now, why does time as measured by a clock slow down or speed up when subjected to a gravitational field? The conventional explanation which naturally follows from GR is that the presence of a massive body shapes or distorts the geometry of space and time. When matter moves through spacetime, it simply follows the geometry of spacetime. This is what gravity really “is” according to GR. Thus, in the case of the clocks at different attitudes, the presence of a massive body (the Earth) causes the geometry of spacetime to be differently shaped at different distances from the center of the Earth, resulting in different rates of change at different altitudes.
Most physicists would agree that it is unreasonable to object to the truth of relativity. Do you agree?
Then you are throwing out empiricism as well. If we aren’t allowed to measure anything with tools then how can anything be empirically verified? What we would be left with is our subjective observations.
I don’t think that gravity is a physical substance either - would you agree? Yet, gravity clearly produces physical effects.
The science fiction scenario of twins where one embarks on a space journey and returns to find his stay-at-home sibling much older than himself would be an empirical verification of the fact that time has slowed down for the travelling sibling.
Of course we don’t have to wait for that to happen - clocks have already been observed to slow down when they travel fast. Obseved - not inferred; just like the temperature change has been observed, not inferred. We can observe the clock’s behaviour without knowing anything about GR theory and without positing any particular cause for the phenomenon. Pure observation.
Why do you find it so odd that time isn’t constant but depends on other factors? This is a very common situation in physics. Gravity isn’t constant either.
Throughout this thread, there seems to be a hazy idea that clocks are slowing down as time slows down in a way that the observer who is travelling along with the clock could detect or sense the slowing of that time. Unless I a mistaken, and then correct me please, time never slows down so far as the one big happy ship of inertial fellow travelers is concerned. Without windows or sensors to the outside universe, passengers of a spaceship in a gravitational field or unaltered velocity would all be convinced that their clocks are completely normal and that time has in fact not slowed down. Atomic clocks, timex watches, pendulums, Olympic records, the subjective experience of duration, advertisements and elections, would all be exactly as they are within that frame.
So Jim, whatever you propose as a physical mechanism, must work in a relativistic fashion, so that clocks are only slowed down in respect to other frames, and not within the frame.
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