Exploring Physicists' Opinion on 'Moving Through Time

[Trysse]

TL;DR Summary

I regularly find the expression that observers or objects "move through time". What do physicists think, when they use, read or hear this phrase?

I recently had a discussion with my brother, about what it means to "move through time". His opinion is, that physicists cannot take this literally. His opinion is, that time is just an expression for change that takes place at different rates for different observers depending on their speed through space. So when physicists say, we are "moving through time" they actually mean, "we change".

I have the feeling that physicists somehow take the "movement" literally. To me, physicists seem to think, that there is a higher (time-)dimension beyond the space we can sense and that we are moving through this higher dimension. At least that is what I get from what I read and hear from textbooks and professional physicists explaining special relativity.

So what do you think? By this question I mean two things: What is your take on "movement through time"*? What do you think physicists think?

Is there a consensus? Is there an ongoing debate about the use of the word "move" in relation to time? If you think, that physicists don't take "move" literally, why are they using this metaphor?

P.S. I am aware, that there is no homogenous group which is "the physicists" so I am probably referring to the mainstream.

P.P.S I know the concepts of spacetime, Minkowski diagrams, and the four-vector. There is no need to explain this or hint at it in your response.

* Are you a professional physicist, whose job is it to ponder those questions? Any opinion is welcome, I am only curious about your status.

 

[Demystifier]

It means that the trajectory of a point particle in spacetime is a curve along which time is not constant.

 

[PeroK]

Summary:: I regularly find the expression that observers or objects "move through time". What do physicists think, when they use, read or hear this phrase?

This is not the sort of question that physicists spend their time debating. In the theory of GR for example, light moves on null geodesics and massive particles move on timelike geodesics. When expressed in mathematical terms there is no debate about what that means.

A question that is of interest is whether spacetime is emergent from a more fundamental theory. Both GR and QFT start with the assumption that there is a spacetime manifold. But, perhaps a theory of quantum gravity might start without this assumption and derive the nature of spacetime from something more fundamental.

Unlike @Demystifier, I'm not a professional physicist.

 

[Demystifier]

Unlike @Demystifier, I'm not a professional physicist.

In basic questions such as this one, amateurs can be as good as professionals.

 

[martinbn]

It means that the trajectory of a point particle in spacetime is a curve along which time is not constant.

It is called world line not trajectory.

 

[Demystifier]

It is called world line not trajectory.

https://www.oxfordreference.com/view/10.1093/oi/authority.20110803124815103

 

[martinbn]

Summary:: I regularly find the expression that observers or objects "move through time".

Only in popular science. In the actual science no one uses this expression. And often in popular science the goal is not to be as precise as possible but to spark the interest of the audience.

I think that it is a phrase that is more confusing than explaining, and physicists who popularize physics can do better.

* I am not a physicist.

 

[italicus]

To be elementary, You move through time from your birth to your death, even staying seated on a chair.
look at your wrist watch from ‘time to time ‘ , the position of its hands changes regularly, hopefully.
According to Newton, time was “ absolute, true, mathematical…” , and together with “absolute space “ was a kind of scenario wrt which the events happen. According to Einstein, time and space are tied in Spacetime (really it was Minkowski to propose this) . Spacetime is absolute, not separated space and time. In any case, your wristwatch time is your proper time, and all observers agree on it.

 

[martinbn]

https://www.oxfordreference.com/view/10.1093/oi/authority.20110803124815103

How did you find that! It is not on the first page when I do a web search. The wiki page says "The concept of a "world line" is distinguished from concepts such as an "orbit" or a "trajectory".."

 

[romsofia]

http://home.uchicago.edu/~geroch/Course Notes

End of page 4, 5 of his general relativity notes cover this for me, very simple and easy explanation.

 

[Orodruin]

To me, physicists seem to think, that there is a higher (time-)dimension beyond the space we can sense

This is an inherent property of special and general relativity. It is not a matter of ”thinking”, it is describing what the models say in layman terms. Not only is time an additional dimension, it is fundamentally linked to the spatial dimensions into what is called spacetime. What appears as the time direction to one observer is not the same as the time direction for another (which will be a linear combination of the first observer’s temporal and spatial dimensions).

 

[anuttarasammyak]

For me something moves through time means that position of something is a function of time. The function is usually continuous and differentiable to some n times.

 

[Trysse]

Thank you all for taking your time and for your answers.

Only in popular science. In the actual science no one uses this expression. And often in popular science the goal is not to be as precise as possible but to spark the interest of the audience.

I think that it is a phrase that is more confusing than explaining, and physicists who popularize physics can do better.

I really agree with your statement, that the phrase to move through time is confusing.

However, I find the same for curved space(time), slicing spacetime, and other similar phrases. I'm not sure these phrases/metaphors are really the best words that could be used to name/describe those concepts of physics respectively physical phenomena.
For me, those phrases make it difficult to distinguish between phenomena and concepts. Another example is the wave function. I am never sure when the word is used, whether it refers to something the can be physically "experienced" or to a concept.

Another word I find highly irritating is manifold, but for the opposite reason. Where phrases like moving through time create pictures in my mind which I think are misleading, the word manifold leaves me without anything to relate to. But this is my personal deficit.

http://home.uchicago.edu/~geroch/Course Notes

End of page 4, 5 of his general relativity notes cover this for me, very simple and easy explanation.

From this document "moving in space as time evolves" is the phrase I can most relate to.

 

[PeroK]

From your introduction.

Hi there,

I am Stefan, I am just starting my third semester of physics at Technische Universität Berlin Germany.

My main interest is the Special Theory of Relativity. Especially, the geometric meaning of the four-vector.

Now you say:

However, I find the same for curved space(time), slicing spacetime, and other similar phrases. I'm not sure these phrases/metaphors are really the best words that could be used to name/describe those concepts of physics respectively physical phenomena.

Another word I find highly irritating is manifold,

You have to sort yourself out. Either you're a serious physics student or not. You should cut the pop-science BS. Sorry for speaking plainly.

 

[Trysse]

You have to sort yourself out. Either you're a serious physics student or not. You should cut the pop-science BS. Sorry for speaking plainly.

Actually, I don't think I have to. But thanks for the advice anyway.

 

[PeterDonis]

I don't think I have to.

You might be misinterpreting @PeroK's statement. He was not saying you need to decide whether or not you are a serious physics student. Based on what he quoted from your introduction, you are a serious physics student; you're in your third semester and you have a special interest in relativity. @PeroK's point is that, since you are a serious physics student, a response like the one he quoted from you--basically, that you don't want to do the work to understand the standard terminology in your field of interest, since all of the terms you mention, "curved spacetime", "slicing", and "manifold", are such standard terminology--is simply not acceptable. You can't be a serious physics student with a special interest in relativity and not learn what those terms mean and what mathematical objects they refer to.

Actually, the only term mentioned in this thread that is not standard terminology in relativity physics is "move through time" (as @martinbn has already pointed out). That is why that term can indeed be troublesome--because, since it has no single precise technical meaning in physics, physicists are free to use it informally to mean whatever they like. The correct response for a serious student of physics with a special interest in relativity is to not pay attention to such terms at all, and to consider any source that uses them to be a pop science source and not acceptable for learning the actual physics. But that just means you need to go look at sources that are acceptable, and those sources, whether you like it or not, are going to use the terms that are standard terminology in the field, like "curved spacetime", "slicing", and "manifold".

 

[ergospherical]

@Trysse one thing my supervisor says sometimes is that 'the formalism exists to help you'! It's certainly possible to learn about relativity by avoiding manifolds and the geometrical concept of spacetime (c.f. Weinberg, 1972 - where gravity is treated as a field theory). However many physicists think that there is much intuition to gained about the equations by viewing the theory through the lens of differential geometry. It's your choice whether to use this tool, though.

 

[Trysse]

I was considering a lengthy response to explain myself. However, I just don't have the time. Whatever that means for a physicist.
Nevertheless, thank you for your time. I do consider what you wrote.
I will sleep tight under the manifold I call my sheet, which locally resembles a Euclidean plane.

 

[dextercioby]

I was considering a lengthy response to explain myself. However, I just don't have the time. Whatever that means for a physicist.
Nevertheless, thank you for your time. I do consider what you wrote.
I will sleep tight under the manifold I call my sheet, which locally resembles a Euclidean plane.

The fact that you have ended with an ironical statement means that you are not really satisfied with the discussion here. Well, this is your choice, this open forum is not to please anyone, really, but to mostly to help the people opening discussions in a way. I hate manifold theory, I think true/advanced differential geometry (fiber bundle formulation of physical theories) is really difficult and I would stay out of it. Weinberg and Dirac were "quantum-ists", wrote books from the point of view of classical field theory with no differential geometry machinery. They wrote books for people like me, who hate diff. geom.

But not everyone is meant to study physics nowadays.

 

[PAllen]

His classic 1972 book on GR, while putting geometry second, and the principle of equivalence first, includes all of the the classical diff. geom. @dextercioby derides (manifolds, curvature, etc.) in a fairly standard way. In this book, his only departure from the geometric approach is to derive it from the POE rather than assume it, and also raise questions about the inevitability of the EFE versus more complicated field equations.

 

[PAllen]

Summary:: I regularly find the expression that observers or objects "move through time". What do physicists think, when they use, read or hear this phrase?

They are thinking, "Oh, I have to write something for a popular audience, let me see what euphemisms have been used before for this, instead of how physicists talk to each other."

 

[vanhees71]

Only in popular science. In the actual science no one uses this expression. And often in popular science the goal is not to be as precise as possible but to spark the interest of the audience.

I think that it is a phrase that is more confusing than explaining, and physicists who popularize physics can do better.

* I am not a physicist.

I couldn't agree more. What I'm wondering about for a long time is, who the heck has got the weird idea that to make science interesting in popular science writing by making it unclear and sounding esoteric. Science should be presented as it is also on a popular level. It's however very difficult to "elementarize" is without making it wrong, but there's no need to represent science as something weird to make it interesting.