What Is the Relationship Between Time and Space in the Universe?

[mdl]

from wikipedia:

... [time] is instead part of a fundamental intellectual structure (together with space and number) within which humans sequence and compare events. This second view, in the tradition of Gottfried Leibniz[15] and Immanuel Kant,[22][23] holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be travelled.

I thought information about space (i.e. matter) exists in the universe regardless of humans. it's maybe in holographic, 1D or other form, but it is stored outside humans.
while information about time is created by humans (by comparing memorised and new information) and exists only "virtually" in our minds.

why are space and time taken as they were both imaginary (the same way)?
if all information about space exists outside humans, how can it be imaginary?

I'm also little confused about whether space-time is a part of the universe or it is only a tool used to describe how space in the universe changes.

thanks

 

[Simon Bridge]

Can a memory of events not exist without humans?

Can we not equally say that positions only exist by humans comparing different locations like they compare different times by consulting memory?

You have to be careful with your definitions.

 

[Drakkith]

I'm also little confused about whether space-time is a part of the universe or it is only a tool used to describe how space in the universe changes.

thanks

Why can't it be both? Our perception of space and time may be unique, but I doubt anyone could claim that spacetime isn't "part of the universe".

 

[Simon Bridge]

I'd have said that the tools for describing how space in the Universe changes are math and language ... the space-time is "out there". But I think that gets bogged down in philosophy.

In fact - that would go with the quotes ... is it possible that OP wants the philosophy forum?

 

[tom.stoer]

The idea to get rid of space and time as physical entities has a long tradition and it has influenced Mach and Einstein as well. Einstein started with a Machian point of view where space and time are not physical entities but all what counts are relations (signals, interactions, ...) of physical entities (bodies, fields, ...).

But as we know Einstein did not "succeed"; the story GR tells us about spacetime is different. Here spacetime seems to be a physical entitry which can exist w/o objects or relation between objects (it cannot be 'observed' w/o test particles, but that's a different story). There are non-rivial vacuum solutions of Einstein's field equations like black hole spacetimes, deSitter universe etc. indicating that (according to GR) spacetime itself is a physical entity (this translates to some quantum gravity approaches like LQG)

 

[ImaLooser]

from wikipedia:


I thought information about space (i.e. matter) exists in the universe regardless of humans. it's maybe in holographic, 1D or other form, but it is stored outside humans.
while information about time is created by humans (by comparing memorised and new information) and exists only "virtually" in our minds.

why are space and time taken as they were both imaginary (the same way)?
if all information about space exists outside humans, how can it be imaginary?

I'm also little confused about whether space-time is a part of the universe or it is only a tool used to describe how space in the universe changes.

thanks

Einstein proved that time was not well-defined, but it works almost perfectly well here on Earth so hardly anyone worries about this.

As to whether concepts correspond with reality, physicists wisely don't worry about that much. If the math works well enough, fine. It is an applied science with practical results, not philosophy.

Since space and time are interdependent, they must have equal ontological status. That is, they must be equally "real" or "unreal," whatever that may mean.

 

[friend]

We have two working theories, QFT and GR. And at some deep level we think there is a connection. It occurs to me that without particles one cannot measure space. If nothing whatsoever existed in space, how could you measure the distance between things? And if particles never moved, how could you measure time? So it seems even at the deepest level there must be things moving in order to measure space and time.

Likewise, if you had no space for things to exist in, how could there be particles? So it seems to me that both are necessary and compliment and complete each other.

 

[ImaLooser]

We have two working theories, QFT and GR. And at some deep level we think there is a connection. It occurs to me that without particles one cannot measure space. If nothing whatsoever existed in space, how could you measure the distance between things? And if particles never moved, how could you measure time? So it seems even at the deepest level there must be things moving in order to measure space and time.

Likewise, if you had no space for things to exist in, how could there be particles? So it seems to me that both are necessary and compliment and complete each other.

Actually there is an important solution to GR called DeSitter space which has no mass. I do not understand it. I guess that you can say how a mass would move if it were there. All GR is built on the idea of these insignificant virtual test masses, so why not use the concept when no mass is there? In both cases we just imagine the test mass is present. It isn't necessary to actually do it.

 

[tom.stoer]

Actually there is an important solution to GR called DeSitter space which has no mass. I do not understand it. I guess that you can say how a mass would move if it were there.

This is exactly what I mean: Einstein did not succeed in building GR on Machian principles only b/c that would rule out vacuum spacetime like deSitter. And yes, of course you can calculate the geodesics on which test particles move in deSitter spacetime.

 

[mdl]

Since space and time are interdependent, they must have equal ontological status. That is, they must be equally "real" or "unreal," whatever that may mean.

i'll try to simplify my thoughts:

- space is a link between two points (or objects)
- time is a link between two events

if a link between two points wouldn't exist, no information/change could propagate from one point into another - so it must exist. for example there's a link between a tree and an apple on ground, because particles/information can propagate between them.

but a link between two events doesn't exist or is unnecessary.
for example link between events "apple is hit by a ball" and "apple falls on ground" doesn't exist. that's why we have developed memory - so that we could create the link.

that's why i think that time and spacetime can't be physical entities..

 

[ImaLooser]

i'll try to simplify my thoughts:

- space is a link between two points (or objects)
- time is a link between two events

if a link between two points wouldn't exist, no information/change could propagate from one point into another - so it must exist. for example there's a link between a tree and an apple on ground, because particles/information can propagate between them.

but a link between two events doesn't exist or is unnecessary.
for example link between events "apple is hit by a ball" and "apple falls on ground" doesn't exist. that's why we have developed memory - so that we could create the link.

that's why i think that time and spacetime can't be physical entities..

I could say that the apple was the link.

I've lost interest. This is like the foggy word games played by old-time philosophers where they would argue endlessly about definitions. Eventually everybody got tired of it and they started using more precise definitions to avoid this sort of thing. Mathematics is nice for that. If you will learn the math, you will get your answer. There are dozens of web sites on special relativity.

 

[Drakkith]

I could say that the apple was the link.

I've lost interest. This is like the foggy word games played by old-time philosophers where they would argue endlessly about definitions. Eventually everybody got tired of it and they started using more precise definitions to avoid this sort of thing. Mathematics is nice for that. If you will learn the math, you will get your answer. There are dozens of web sites on special relativity.

I agree. Learning the math or at least the terms used in science and philosophy will go a long way in letting your get your point across clearly MDL. You may also develop a new understanding as you learn.

 

[Naty1]

Sure seems like in GR space and time are as 'real' [or imaginary, if you wish] as anything else.

Want to create a particle: accelerate. Want to slow down time...go faster and or find a deeper gravitational well...to change mass to energy...E=mc

What to change distance...go faster...

perception seems to be reality...

From QM: If a system is in a state described by a vector in a Hilbert space, the measurement [observation] process affects the state in a non-deterministic, but statistically predictable way...again, 'differences' appear...

I saved this from another discussion:

So the rule for objectivity is not that everyone lives in the same reality, it is that no two observers' realities can be inconsistent with each other. This also means that "complete" information does not imply a unique description of the reality, it merely implies access to all the information that is locally available to that observer in principle. The locality of the information is what preserves causality…”

 

[Simon Bridge]

Want to create a particle: accelerate. Want to slow down time...go faster and or find a deeper gravitational well...to change mass to energy...

What to change distance...go faster...

I suspect you are reading more into GR than is there.

How would you slow time by changing speed?

 

[tom.stoer]

... that's why i think that time and spacetime can't be physical entities..

I think you should try to understand at least the basic mathematical concepts what spacetime according to GR - and possibly some theories of quantum gravity - are. Then your ideas would have a more solid basis.

 

[chiro]

I'd be interested to hear (especially by the physics people) what being physical actually means.

Does it mean it can have a physical interaction? Does it mean it can be observed? Does it just mean that it can be described in some linguistic context and framework? Does it have to be measureable with specific measuring devices?

What does it mean for something to be physical in a highly specific (i.e. non-vague) way?

 

[tom.stoer]

What does it mean for something to be physical in a highly specific (i.e. non-vague) way?

This is unfortunately not a physical but a metaphysical question; for an answer or explanation on must rely (implicitly or explicitly) on a philosophical position like Platonism, positivism, structural realism, ... In addition one must explain the words "physical", "real", "existing", "measurable" and their relation, which is again beyond physics.

Spacetime is a good example: its obviously "physical" or "real" in the sense that we are able to use it a mathematical framework to describe theories with experimentally testable predictions. But it is not "real" in the sense that it can be measured w/o referring to (the motion of) test particles or something like that. The mathematical structure of spacetime (the metric tensor in GR) is not an "observable" due to several reasons.

I am afraid this is not the intended answer ...

 

[Drakkith]

Thank you Tom, I spent a few minutes attempting to say exactly what you did, but I suffer from an inability to explain my ideas well, so I had to give up.

 

[chiro]

Well if something is so vague that it can't be defined, how is one able to actually discuss anything related to this "something"?

If physics can't say what something physical actually is, then I think that this is really an embarrassing situation for the physics people.

For instance, the idea of measurability is where you are able to map some observation of some sort to an element usually in a set of numbers. It's basically identifying something in one language with something in another and in number systems with rank (like the 1 dimensional number systems), we can describe how to classify each element relative to the others by use of ordering and relations like <, >, = and so on.

Now you can formalize this with sets if you want, but intuitively for most purposes, this is enough to explain in detail what measuring does in an abstract sense using spoken languages as opposed to the mathematical one.

If you have a situation where physics can't describe what is physical, then IMO you don't really have physics but something way too vague.

 

[Drakkith]

If physics can't say what something physical actually is, then I think that this is really an embarrassing situation for the physics people.

Why? Because we recognize that when you get right down to some of the fundamentals it becomes hard to give concrete answers? This has always been the case. Thinking that there should always be a definite concrete answer for everything is simply unrealistic. It ignores a great many other issues that make it hard to answer.

If you have a situation where physics can't describe what is physical, then IMO you don't really have physics but something way too vague.

We don't require that something "be physical" in order to measure it. We can measure where an electron is at, it's velocity, its spin, but whether it is "physical" or not delves into other areas like philosophy. If an electron is composed of nothing but fields, is it "physical"? I don't know. That's probably why we don't have a specific definition for physical that I know of.

 

[tom.stoer]

Well if something is so vague that it can't be defined, how is one able to actually discuss anything related to this "something"?

...

If you have a situation where physics can't describe what is physical, then IMO you don't really have physics but something way too vague.

That may be your impression, but please keep in mind that - although lacking a "physical definiton of physical" - the physics community making progress regarding experimentally testable predictions. Einstein and Heisenberg had a debate where Heisenberg intended to ground a theory (of quantum mechanics) purely on measurable quantities. Einstein argued that this approach leads to nothing and that (to some extend) it's the theory which "decides" what is measurable. Now we have a theory of quantumm mechanics based (to a large extent) on mathematical entities which are not measurable (wave functions, density operators, entangled states, time evolution operator, Greens functions, path integrals, ...) but from which we can extract measurable predictions which are proven to be "correct". So the question whether these "not measurable quantities" are "unphysical" is a metaphysical question which seems to be irrelevant for the success of physics.

 

[chill_factor]

That may be your impression, but please keep in mind that - although lacking a "physical definiton of physical" - the physics community making progress regarding experimentally testable predictions. Einstein and Heisenberg had a debate where Heisenberg intended to ground a theory (of quantum mechanics) purely on measurable quantities. Einstein argued that this approach leads to nothing and that (to some extend) it's the theory which "decides" what is measurable. Now we have a theory of quantumm mechanics based (to a large extent) on mathematical entities which are not measurable (wave functions, density operators, entangled states, time evolution operator, Greens functions, path integrals, ...) but from which we can extract measurable predictions which are proven to be "correct". So the question whether these "not measurable quantities" are "unphysical" is a metaphysical question which seems to be irrelevant for the success of physics.

But then you also have things that are predicted and undetectable even in principle such as gravitons, dark matter and much of high energy theory.

Also, the basic wave mechanics of quantum mechanics can already tell you alot, and wave mechanics is pretty easily visualized and even experimentally seen. There's even photos of wavefunctions (given by electron distributions) in metal clusters, graphene and even individual organic molecules.

The bra-ket notation and matrix mechanics served to *make QM less intuitive and harder to visualize*. However it did clean up a lot of the integrals and make certain things easier to calculate. In materials science and chemistry though, wave mechanics is used more often since it its an easier (not easy) way to calculate applied problems such as molecular clusters, polymers, and complicated nanostructures. Bra-ket notation is still important for other uses such as NMR off the top of my head. but if you don't use those specific tools you only need wave mechanics.

I'm in physics and I'm find that the way quantum mechanics is taught in physics is wayyyy different from the way its taught to chemists and materials engineers, and it is taught that way to make it easier for the theorists, not experimentalists. That's a shame because without experiment, there's no science, industry or technology, just a bunch of arcane symbols. Just my opinion.

 

[chiro]

Why? Because we recognize that when you get right down to some of the fundamentals it becomes hard to give concrete answers? This has always been the case. Thinking that there should always be a definite concrete answer for everything is simply unrealistic. It ignores a great many other issues that make it hard to answer.

The less specific something is, the more useless it becomes when it comes to not only defining something, but making use of something particular for analysis and inference/decision making of any sort.

There are different levels of specificity and while I agree that things are always being clarified a constant basis, having some basic idea of what a physical thing is is not much of an ask for something that has been developing for many hundreds of years.

It's a good idea for the physicists to do this anyway because it helps them clarify what they are looking at and doing this will actually lead to solving the problems that exist.

You can't solve a problem that you can't define, and science (and mathematics and life in general) is all about solving problems and dilemmas.

If it's hard to give explicit answers, maybe a definition involving measureability with specific kinds of information can be given about what physics measures and studies. How about something like that?

Again, the more vague someone is, the more useless they are in making their point.

We don't require that something "be physical" in order to measure it. We can measure where an electron is at, it's velocity, its spin, but whether it is "physical" or not delves into other areas like philosophy. If an electron is composed of nothing but fields, is it "physical"? I don't know. That's probably why we don't have a specific definition for physical that I know of.

But you can constrain the linguistic and informational constraints that are being talked about.

Everything is information and you can classify information. We create languages that take a subset of all classifications and create ways to subdivide those classifications all the time whether its mathematically or non-mathematically.

What you have implied above is that there is some kind of line (but you haven't been specific enough) that divides philosophy and physics on the basis that physics is associated more or less with measurability but not with the nature of what information actually is.

In other words physics considers information, its sources, how to measure them, and subsequent analysis of such information but there is a line drawn where it comes to thinking about what information actually is in terms of some kind of other meaning.

Now if you want to get more specific, then what you should do is discuss meaning in the context of an interpretation to get that line more formally defined.

If you making a specific kind of interpretation that is philosophy then so be it, and if it's physical then so be it, but there must be a line that gets more clarified as times goes on.

Information itself can be taken as simply information in some particular context and it's done all the time through the language that is used: you simply look at the language used and then derive the interpretative context that this particular form of analysis is bound by.

You take one particular context, you get interpretation and then you get a way to find that line. You take another and you get similar properties for that context. They may overlap, they may not.

At the very least though, one can consider firstly the information context associated with what physics tries to describe and then work from there.

 

[harrylin]

[..] a link between two points [..] must exist.
[..] but a link between two events doesn't exist or is unnecessary. [..]

Hi mdl,
"space"* and "time" are human concepts that relate to the "real" physical world in a way that is not fully understood (at least not by all) and which are even open to modification. There certainly exist physical-philosophical papers on that, for example "The evolution of Space and Time":
http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

*physical space, to be distinguished from mathematical space

EDIT: IMHO this topic is just in the realm of science

 

[Naty1]

How would you slow time by changing speed?

time dilation.

I'd be interested to hear (especially by the physics people) what being physical actually means.

skirting the issue of an exact definition, something is 'physical' if we can measure/observe it. Otherwise it's just theory. A fly in the ointment is that different observers have, in general, different observations.

For example, in the quantum field theory view, "real particles" are viewed as being detectable excitations of underlying quantum fields. The physical existence of the underlying fields is unproven.

 

[Drakkith]

The less specific something is, the more useless it becomes when it comes to not only defining something, but making use of something particular for analysis and inference/decision making of any sort.

There are different levels of specificity and while I agree that things are always being clarified a constant basis, having some basic idea of what a physical thing is is not much of an ask for something that has been developing for many hundreds of years.

I don't disagree, but I think that you misunderstand. When we measure something we are measuring one or more properties of the object, such as the spin of an electron or the mass of a proton. Nowhere do we measure "physicalness", IE we cannot measure whether something is physical or not because it is not a measurable property. You cannot plug physicalness into an equation and get an answer. You can say that if you can measure and observe something directly that it is physical, however I think that is up to interpretation.
So while the question of whether an object is physical or not may be vague, our measurements of its properties are not vague at all.

In the end I don't think it matters whether you call something physical or not. It doesn't change the way it works in any way, similar to how calling something red as opposed to orange-red depends entirely upon the person viewing it. It doesn't change any experiments if you call something physical or not, nor does it change the way we use something. An electron is used exactly the same way in a transistor whether we call it physical or not. So if it makes no difference if we call something physical or not, why is it an issue?

It's a good idea for the physicists to do this anyway because it helps them clarify what they are looking at and doing this will actually lead to solving the problems that exist.

You can't solve a problem that you can't define, and science (and mathematics and life in general) is all about solving problems and dilemmas.

I don't follow you. How does labeling something physical make any difference on our ability to solve problems? What problems can we not define without a specific definition for physical?

What you have implied above is that there is some kind of line (but you haven't been specific enough) that divides philosophy and physics on the basis that physics is associated more or less with measurability but not with the nature of what information actually is.

To my understanding science is a subset of philosophy that deals with empirical things, IE things that are measurable. In my opinion the question of whether something is physical or not is more of a philosophical question since I don't think it matters either way to science, as it doesn't change anything we do.

 

[chill_factor]

In the end I don't think it matters whether you call something physical or not. It doesn't change the way it works in any way, similar to how calling something red as opposed to orange-red depends entirely upon the person viewing it. It doesn't change any experiments if you call something physical or not, nor does it change the way we use something. An electron is used exactly the same way in a transistor whether we call it physical or not. So if it makes no difference if we call something physical or not, why is it an issue?
I don't follow you. How does labeling something physical make any difference on our ability to solve problems? What problems can we not define without a specific definition for physical?
To my understanding science is a subset of philosophy that deals with empirical things, IE things that are measurable. In my opinion the question of whether something is physical or not is more of a philosophical question since I don't think it matters either way to science, as it doesn't change anything we do.

I believe it does. I'd say science is not a subset of philosophy that deals with empirical things; it is a subset of engineering that deals with fundamental limits instead of practical limits. The role of science is to find the fundamental limits and push the fundamental limits of technology to create useful products and services. That's the view of Germans in the 19th century and why industry sponsored scientists.

As such, the physicality (observability) of the systems we deal with is important. At the end of the day science is not philosophy because science is about data. However, theoretical physics, especially high energy physics, is not! Almost all of the things they predict will NEVER be seen and can NEVER be seen. Even the meager few experiments CANNOT be replicated for all intents and purposes because the equipment used is so expensive, and thus there is no real "peer review" and "reproducible" data.

I believe theoretical physics (all fields) and high energy in particular is broken. They predict things unobservable *even in principle* (it is not possible to build a detector for them). We are not talking electrons or photons here. Those are clearly observable. In fact the driving force for theorizing them was *actually seeing them*. Half of physics moved beyond what is observable and into what is not about 50 years ago.

Just read some arXiv high energy, cosmology, etc. papers and tell me with a straight face that if those disappeared tomorrow, the world would be a worse place.

 

[tom.stoer]

You address some import issues, and - at least partially - I can agree:

I'd say science is not a subset of philosophy that deals with empirical things ... The role of science is to find the fundamental limits and push the fundamental limits ... That's the view of Germans in the 19th century ...

As such, the physicality (observability) of the systems we deal with is important. At the end of the day science is not philosophy because science is about data ...

If you replace "physical" by "observable" or "measurable" I think everybody can agree.

However, theoretical physics, especially high energy physics, is not! Almost all of the things they predict will NEVER be seen and can NEVER be seen.

That is not true if you use "predict" in the correct way. High energy physics uses concepts like quantum gauge fields, quarks, gluons etc. to predict observable and measurable entities like multiplets, sum rules, masses, cross sections, form factors and structure functions etc. In that sense the mathematical entities the theory is based on are not observable, but the data (the predictions) are.

Even the meager few experiments CANNOT be replicated for all intents and purposes because the equipment used is so expensive, and thus there is no real "peer review" and "reproducible" data.

They constantly reproduce things! All major results (particles and their properties) have been observed at different experiments, at different colliders, and their extraction is based on different technology and data analysis.

I believe theoretical physics ... and high energy in particular is broken.

As I said: theoretical physics does not predict the entities it uses, it simply uses them as mathematical structures in certain models; as an exmaple: perhaps QCD is wrong and quarks and gluons "do not exist".; but in order to convince me you have to show me
a) at least one experimental result which is in conflict with QCD
b) a structurally different theory (model) with different mathematical entities which can reproduce a) and all other predictions of QCD

They predict things unobservable *even in principle* (it is not possible to build a detector for them).

As I said: they do not predict these entities but they use them; that's different. Yes, there are many important entities that are unobservable in principle (the wave function is a good example) but nevertheless these entities are required to make experimantally testable predictions.

Last but not least: I agree that some approaches of modern physics became highly speculative and the wording regarding "predictions", "existence" etc. is partially is inappropriate and is interspersed with advertising and marketing. But that does NOT apply to "theoretical physics (all fields) and high energy". Models used in high energy physics, their application and their results are nearly as reliable as applied quantum mechanics.

 

[SW VandeCarr]

I'd be interested to hear (especially by the physics people) what being physical actually means.

Does it mean it can have a physical interaction? Does it mean it can be observed? Does it just mean that it can be described in some linguistic context and framework? Does it have to be measureable with specific measuring devices?

What does it mean for something to be physical in a highly specific (i.e. non-vague) way?

It might be as simple as what Lord Kelvin (William Thomson) said in the 19th century. To be an object of science, you must be able to measure it (implying some kind of consistency of observations).

 

[chill_factor]

You can directly image the result of wavefunctions though; scanning probe microscope photos have been taken of electron density distributions in organic molecules and semiconductor nanostructuers.

So this is what I mean by "detect" and "observable". You can seriously see the wavefunction - the absolute square of it. Good enough as seeing the real thing. That is why we know it exists.

Lets take the graviton instead. To distinguish a graviton signal from a neutrino signal would require shielding that would collapse into a black hole. Therefore the graviton is not observable in principle. http://arxiv.org/abs/gr-qc/0601043

How many things are simply not observable because their detection or creation has unphysical requirements or even physically impossible requirements?

I'm not an expert but, from what I've heard about high energy, you can get totally different results simply from using different statistical methods.

 

[tom.stoer]

You can seriously see the wavefunction - the absolute square of it.

Sorry to say that, but that's a huge conceptual difference.

Lets take the graviton instead. To distinguish a graviton signal from a neutrino signal would require shielding that would collapse into a black hole. Therefore the graviton is not observable in principle. http://arxiv.org/abs/gr-qc/0601043

I am sorry but as long as there is no reliable theory of quantum gravity which explains what the "mathematical entity graviton" means we cannot safely say whether a "graviton as physical entity" does exist. In addition it may very well be that the final theory of quantum gravity does not even contain a graviton as fundamental d.o.f., therefore it could be that it does neither exist mathematically nor physically and that there is no such problem at all.

How many things are simply not observable because their detection or creation has unphysical requirements or even physically impossible requirements?

A lot - but why should we care? OK, you may complain about the fact that a specific theory (which one?) contains too many unphysical entities and that (according to Ockhams razor) it should be replaced by something which is less wasteful ontologically. Of course you are invited to develop such a theory (what do you have in mind?).

 

[nitsuj]

chill_factor - What about a photon moving at c, it's not observable between events. What do you make of this stuff that separates events?

 

[Drakkith]

I believe it does. I'd say science is not a subset of philosophy that deals with empirical things; it is a subset of engineering that deals with fundamental limits instead of practical limits.

I think you should review what engineering and science are. Here are a couple of links.
http://en.wikipedia.org/wiki/Engineering
http://en.wikipedia.org/wiki/Science

As such, the physicality (observability) of the systems we deal with is important. At the end of the day science is not philosophy because science is about data.

Here's a link to philosophy. And on the philosophy of science.
http://en.wikipedia.org/wiki/Philosophy
http://en.wikipedia.org/wiki/Philosophy_of_science

Just read some arXiv high energy, cosmology, etc. papers and tell me with a straight face that if those disappeared tomorrow, the world would be a worse place.

It would be, for we would not know what paths have already been taken.