Do we have to accept the physical existence of time?

[learning]

So, I am confused about the following.I learned in high school and in my first year of university that there is something called time dilation that observers observe that time is slower for objects that are moving faster. As in if there were two initially synchronized clocks that you could perfectly see that were moving towards you let's say the one which was faster would be slower. I also learned the idea of a space time invariancy. I don't really know how General relativity is supposed to work in full detail other than an accelerating frame in space is no different than one which is experiencing gravity and somehow this makes it so that time is slower with greater gravitational force.

I wanted to know if these imply that time "physically" exists. What I mean is that we have to accept time as something more than just potential energies turning into kinetic energies thus causing motion and interaction of a particular sort making us perceive that there is a future.

Which is not a very good description but what I mean is that is there a concept of time that physically exists beyond the interactions of objects.

I think my question boils down to: Do we know that time physically exists and its not just:
a. objects appearing to move slower because they get more mass relatively speaking as they move faster but as intrinsic energy or momentum is conserved they move intrinsically slower so making it appear that time dilates.
b. As something moves faster in the universe it appears to experience a "restrictive measure" by the universe like "the doppler effect" in sound and this is why things appear to move slower.

I know I only made the argument for special relativity but I imagine the same thing for gravity as well.

I will admit that I find it difficult to accept the concept of "physical time" as I cannot imagine that moving down a axis on a graph and you get a universe with me in it a few moments from where I was and that simultaneously there are an infinite number of universes existing.

I just can't convince myself into believing it without knowing why I am believing it. Any help is appreciated. Thanks in advance.

 

[Dale]

Do we know that time physically exists

Yes. We say that something physically exists if we can build a physical device which measures it. In the case of time such devices are called clocks.

 

[learning]

Yes. We say that something physically exists if we can build a physical device which measures it. In the case of time such devices are called clocks.

So time could be or is nothing more than the proportion of a set distance to a set speed. which we define from energy or momentum and not time? I mean is this interpretation is valid? We don't have to believe that it physically exists apart from this.That it is not intrinsic to reality but implied by other things.

 

[Dale]

I am unwilling to make any philosophical statements about “intrinsic to reality” or any other such metaphysical nonsense. This is science and in science we are concerned with what can be reproducibly measured in experiments. A thing that can be measured, like time, is physical regardless of any philosophical hand-wringing.

 

[Nugatory]

So time could be or is nothing more than the proportion of a set distance to a set speed. which we define from energy or momentum and not time? I mean is this interpretation is valid? We don't have to believe that it physically exists apart from this.That it is not intrinsic to reality but implied by other things.

This is a good moment to quote one of Einstein's most insightful but least well-appreciated (by laypeople - experts in the field appreciate it just fine) remarks: "Time is what a clock measures".

Any time-dependent process - the ticking of an insanely accurate atomic clock, the beating of my heart, the swing of a pendulum in a grandfather clock, the rate of growth of my dog's toenails, the increase in the bacterial burden in the piece of meat I forgot to put in the refrigerator last night, the radiation coming out of a sample of material with a given radioactive half-life, sand flowing through an hourglass, the movement of the shadow on a sundial - can be used as a clock to measure something that we can call the passage of time. Does that mean that time "physically exists" (your words, not mine)? Don't know, not even sure that I know what that question might mean.

 

[learning]

This is a good moment to quote one of Einstein's most insightful but least well-appreciated (by laypeople - experts in the field appreciate it just fine) remarks: "Time is what a clock measures".

Any time-dependent process - the ticking of an insanely accurate atomic clock, the beating of my heart, the swing of a pendulum in a grandfather clock, the rate of growth of my dog's toenails, the increase in the bacterial burden in the piece of meat I forgot to put in the refrigerator last night, the radiation coming out of a sample of material with a given radioactive half-life, sand flowing through an hourglass, the movement of the shadow on a sundial - can be used as a clock to measure something that we can call the passage of time. Does that mean that time "physically exists" (your words, not mine)? Don't know, not even sure that I know what that question might mean.

I am unwilling to make any philosophical statements about “intrinsic to reality” or any other such metaphysical nonsense. This is science and in science we are concerned with what can be reproducibly measured in experiments. A thing that can be measured, like time, is physical regardless of any philosophical hand-wringing.

Okay, I think I am starting to get a good idea now of what I am really trying ask. Using an analogy from another area of physics: There is the concept of temperature. Difference in temperature causes transfers of heat. This can be used to power heat engines. it can be measured by a thermometer. but to me temperature doesn't "physically" exist. This is because it is a statistical phenomena caused by kinematics of particles and a variety of other underlying physics. I am not trying to be philosophical at all. If I say that some object has more negative charge then I imagine a fundamental property that electrons and protons possesses and that one object has a greater difference in the amount of electrons and protons it possesses than the other.

So what I am trying to get to is:
Is it that Time = Distance/Velocity or is Velocity = Distance / Time. or is the answer that physics doesn't really care as long as it produces the same predictions. And if it is the case that physics doesn't care as long as it produces the same predictions than do they produce the same predictions? What I mean is that does special and general relativity heavily favor one interpretation over the other?

 

[Dale]

it can be measured by a thermometer. but to me temperature doesn't "physically" exist.

That is just silly. If you can measure it then it is physical. Do you think thermometers conduct a seance to get their readings from ghosts?

So what I am trying to get to is:
Is it that Time = Distance/Velocity or is Velocity = Distance / Time.

That is a distinction without a difference.

 

[learning]

That is just silly. If you can measure it then it is physical. Do you think thermometers conduct a seance to get their readings from ghosts?

That is a distinction without a difference.

Thank you. I was trying to know if there was absolutely no difference in the physical predictions of the interpretations. I think that you are saying that there is absolutely no difference. That is what I was concerned about.

As for you actual point, I might be wrong I don't wish to speak for you but I think that you are trying to tell me that physics is only concerned about its own mathematical model based upon optimizing predictive results and that beyond that conflating the concepts of the physical model to approximations of the underlying truth of reality is not in physics but philosophy. In essence if the natural world is a black box like machine which takes in phenomena and outputs phenomena than physics is only concerned with the mathematical model of best predicting the output and does not say anything about the inner workings of the box. That the models in physics are not approximations to those inner workings and are totally independent and seperate.
Did I get it right?

 

[jtbell]

underlying truth of reality

If we were to find the "underlying truth of reality", how would we know that we have done it?

 

[learning]

If we were to find the "underlying truth of reality", how would we know that we have done it?

I think that there is a distinction between saying "I think this is what the natural world is." and "I think this is how the natural world behaves.".
If we were to go with the former we wouldn't be able to know whether or not it is the truth but we could say I think that this is our best guess at what the truth is. I also think that there are differences in implications as well. The reason why I was so interested in this question about time was because if it does exist physically that could allow for things such as reverse causality something in the "future" affecting the "past". Whereas if it doesn't exist we could say that reverse causality isn't real as time is a mathematical fiction we use to help make the equations work better and better predict the outcomes of events.

 

[Orodruin]

So time could be or is nothing more than the proportion of a set distance to a set speed.

Technically, with our current length and time units, it is the other way around. A meter is the distance light travels in 1/299792458 seconds.

 

[PeroK]

I think that there is a distinction between saying "I think this is what the natural world is." and "I think this is how the natural world behaves.".

There is an important distinction. The first is a philosophical question, sometimes called metaphysics. The second is what physics deals with.

 

[learning]

There is an important distinction. The first is a philosophical question, sometimes called metaphysics. The second is what physics deals with.

I see. This does make all the replies that I have gotten make sense. All this time I thought that the whole idea about physics was to find the inner workings of the natural world. lol. I started learning physics in middle school. Before I decided to become a programmer changed my major to comp sci I wanted to be a physicist. I have spent over 10 years of my life not knowing this. This should be like the #1 first thing that they teach.

 

[FactChecker]

How can one talk about "speed" or "velocity" or "before" and "after" without first defining time? I can't see any alternative. If you hypothesize an alternative, you need to define it in very concrete terms. There are many coordinate systems that can be used to represent a location in space-time. Including time as a dimension is very useful and fundamental.

 

[andrew s 1905]

Time is defined in a way to make the description of motion as simple as possible. That is how you can tell a good clock from a bad one.

If you used my pulse it would make a pendulum appear to speed up and slow down as I exercised but if you used an atomic clock it would seem much more regular with small fluctuations - some due to the tides!

Regards Andrew

 

[bhobba]

As Nugatory said Einstein gave the best explanation - Time is what a clock measures. The following goes somewhat beyond that at a beginner level and basically reaches the conclusion - that's pretty much the best you can do:
https://www.amazon.com/dp/0393285235/?tag=pfamazon01-20

As for relativity its not so much about time as, like a lot of physics believe it or not, about symmetry:
http://www2.physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

QM and symmetry each by itself is very interesting but when combined our most powerful theories emerge. This causes some to think they have seen the outline of the deep 'whatever it is' that lies at the rock bottom of reality (reality is a word like time, very hard to pin down exactly, which is why it should be used sparingly in physics). The following is a good book about this at a more popular level:
https://www.amazon.com/dp/0691173265/?tag=pfamazon01-20

I am re-reading the latest edition right now while relaxing a bit after lunch before driving home:

At a more advanced level, while not everyone here agrees how good it is (not in the sense of being wrong or anything like that - but being perhaps a bit simple for the importance of the material) I like the following:
http://physicsfromsymmetry.com/

Personally I would read both - first Fearful Symmetry, then Physics From Symmetry.

The interesting thing is once you focus on symmetry and its importance questions like what is time etc do not seem much of an issue. Especially since as the first book I referenced that goes deeply into it concludes, nobody has really got much beyond - Time Is what a clock measures.

Physics can be like that for foundational questions that beginners think are really important - they turn out to be not much of a worry. And as we understand where the universe came from better (from the big bang where time itself was born) then - (if then is an appropriate term here) things may be clearer. But note - when time came into existence is rather nebulous without the concept of time - which is one of the issues of getting to grips with what it actually is. It may be one of those fundamental things that every theory assumes - they all must assume something. Or it may come about from something else like the false vacuum (look it up for more detail). You may find Hawking's Lecture on it of value:
http://www.hawking.org.uk/the-beginning-of-time.html

Sorry physics can't be more helpful on the issue - its just one of those things very hard to pin down.

Thanks
Bill

 

[Dale]

conflating the concepts of the physical model to approximations of the underlying truth of reality is not in physics but philosophy.

Correct. The easier way to make the distinction (in my opinion) is through considering experiments. If you could in principle make an experiment that would answer the question then the question is scientific since it can be addressed through the scientific method.

Truth and reality are not scientific concepts, they come from philosophy, specifically from the philosophical discipline of metaphysics. There is no truthometer or realitometer.

 

[Klystron]

I see. This does make all the replies that I have gotten make sense. All this time I thought that the whole idea about physics was to find the inner workings of the natural world. lol. I started learning physics in middle school. Before I decided to become a programmer changed my major to comp sci I wanted to be a physicist. I have spent over 10 years of my life not knowing this. This should be like the #1 first thing that they teach.

Computer science provides many examples of clocks and synchronization. Operating systems synchronize -- provide timing signals and measures -- to processes and data. Time stamps abound as an attribute of data files and packets. Large distributed systems spend nearly similar resources 'timing' as computing. Ethernet and TCP/IP coordinate communication via time marks and synchronization.

Stepping through processes, say using a debugger, taught me about the inner working of synchronization and time. Hope this helps the OP answer the question.

 

[stevendaryl]

This is a good moment to quote one of Einstein's most insightful but least well-appreciated (by laypeople - experts in the field appreciate it just fine) remarks: "Time is what a clock measures".

I think that that pithy quote is a little misleading, because there is a “time” appearing in the Lorentz transformations that is not (directly) what a clock measures. $\tau$ (proper time) is what a clock measures, but $t$ (coordinate time) is a result of synchronization of multiple clocks, and isn’t directly anything measured by clocks.

 

[Arkalius]

I think that that pithy quote is a little misleading, because there is a “time” appearing in the Lorentz transformations that is not (directly) what a clock measures. $\tau$ (proper time) is what a clock measures, but $t$ (coordinate time) is a result of synchronization of multiple clocks, and isn’t directly anything measured by clocks.

But there always exists a frame of reference where a particular coordinate time is the proper time that a clock could measure. Just because we can mathematically come up with quantities of time that wasn't measured by a particular clock doesn't mean it couldn't have been.

Ultimately I think it's fair to say that time is as physical as space or distance is. Distance seems more real to us because we can observe things across many distances in 3 different dimensions simultaneously. But, we are anchored in a singular moment in time. Sure, we are aware of the past and can anticipate the future, and sense how we move through one and leave behind the other but now is the only moment that "exists" in a significant way for us.

 

[stevendaryl]

But there always exists a frame of reference where a particular coordinate time is the proper time that a clock could measure.

Suppose some event takes place on the Earth, $e_1$. Some other event takes place in the Andromeda galaxy, $e_2$. Your coordinate system might tell you that the time between these events is 1 second. But no clock can measure that time difference, because no clock can be at both events (it would have to travel faster than light) So that time difference is not something measured by a clock.

 

[Nugatory]

So that time difference is not something measured by a clock.

Indeed it is not... so if time is what a clock measures, then that difference isn't time, right? :)

And seriously, kidding aside, one of the things I like about Einstein's sound bite is that it implies the distinction between proper time and coordinate time and drives us to the realization that only one is a physical phenomenon.

 

[JMack]

Hopefully this is on-topic enough to post in this thread and not create a new one... sorry to the OP if I'm taking anything away, but, to the experts...

With the example of a moving photon clock, the clock is measuring time dilation in that it takes longer for the clock to register a "tick" because of the increased distance the photon has to travel. I'm probably misinformed somehow in my reasoning, but can you somehow say that the clock is measuring distance? Is this kind of what is meant by saying space and time are one, not separate?

And in G.R. time dilation occurs because of stretching of space? Does this mean that for a stationary photon clock, the distance between where the photon is emitted and the mirror is greater(stretched)? Causing it to take longer to register "ticks?"

 

[Dale]

But there always exists a frame of reference where a particular coordinate time is the proper time that a clock could measure.

I would be cautious about that claim. The proper time is only defined on the worldline of the clock. The coordinate time is defined throughout spacetime. There do exist many coordinate systems that agree with the proper time of the clock on the worldline of the clock, but that does not make the coordinate time the same as the proper time in general since they are functions with different domains.