Question on Spacetime

roosh

Just a quick question, with regard to how time is treated with regard to General Relativity.

How does the inclusion of time (in spacetime), affect the GR equations, with regard to expansion and contraction of the universe.

Apologies if this isn't the best phrased question.

I suppose what I am trying to get at, is, if time is unbundled from spacetime, would the equations still show us to be in an expanding universe?

I understand this comes across as "crackpottery", but as a completely theoretical query, if you could indulge me, that would be much appreciated.

Professor_Fink

mangaroosh wrote: »

How does the inclusion of time (in spacetime), affect the GR equations, with regard to expansion and contraction of the universe.

...

I suppose what I am trying to get at, is, if time is unbundled from spacetime, would the equations still show us to be in an expanding universe?

That's not exactly how general relativity works. In GR you have field equations which determine the structure of the spacetime. It isn't possible to separate time from space, the equations simply don't make sense.

The expansion of the universe is simply the way the slice of spacetime (i.e. the space bit) that we perceive is increasing as we follow a timelike curve through the spacetime manifold.

A simple example of this is to imagine spacetime as a ball. imagine a line through the ball joining two points on the surface of the ball, passing directly through the ball. If we take a 2D slice perpendicular to this line, the area increases as we move along the line until we reach the mid point. This is essentially what cosmic expansion is, although spacetime isn't really shaped like a ball.

roosh

Professor_Fink wrote: »

That's not exactly how general relativity works. In GR you have field equations which determine the structure of the spacetime. It isn't possible to separate time from space, the equations simply don't make sense.

The expansion of the universe is simply the way the slice of spacetime (i.e. the space bit) that we perceive is increasing as we follow a timelike curve through the spacetime manifold.

A simple example of this is to imagine spacetime as a ball. imagine a line through the ball joining two points on the surface of the ball, passing directly through the ball. If we take a 2D slice perpendicular to this line, the area increases as we move along the line until we reach the mid point. This is essentially what cosmic expansion is, although spacetime isn't really shaped like a ball.

Ok, but in the hypothetical scenario that time were found to be non-existent, what effect would this have, or would it have any at all?

Professor_Fink

mangaroosh wrote: »

Ok, but in the hypothetical scenario that time were found to be non-existent, what effect would this have, or would it have any at all?

If in the future time were to be found not to exist? The sentence doesn't even make logical sense. Of course time exists.

roosh

Professor_Fink wrote: »

If in the future time were to be found not to exist? The sentence doesn't even make logical sense. Of course time exists.

Ok, if time is found to be non-existent, what would be the implications?

Turtwig

mangaroosh wrote: »

Professor_Fink wrote: »

mangaroosh wrote: »

Ok, but in the hypothetical scenario that time were found to be non-existent, what effect would this have, or would it have any at all?

If in the future time were to be found not to exist? The sentence doesn't even make logical sense. Of course time exists.

Ok, if time is found to be non-existent, what would be the implications?

An infinite loop would result perhaps..
Sorry, couldn't resist.
*gets coat*

Professor_Fink

mangaroosh wrote: »

Ok, if time is found to be non-existent, what would be the implications?

Mangaroosh, your question doesn't make sense. If time didn't exist, then there would be no future, so you can't discover something in the future. It's like asking what would happen if you discovered you didn't exist.

Kevster

...well my watch has stopped and that's indication enough that time has ceased to exist :P

mangaroosh, if time didn't exist, then the Universe would just be static, where nothing changes. It'd be like hitting the pause button, surely? Time is a fundamental requirement for the Universe. It simply cannot exist without it.

roosh

Professor_Fink wrote: »

Mangaroosh, your question doesn't make sense. If time didn't exist, then there would be no future, so you can't discover something in the future. It's like asking what would happen if you discovered you didn't exist.

Nothing can be discovered in the future. When any discovery is made, it is always the present (not the present moment in time).

Not to get bogged down in that though. Lets just say that you make a scientific discovery now, that time doesn't exist, what would be the effect on the General Relativity equations?

roosh

Kevster wrote: »

...well my watch has stopped and that's indication enough that time has ceased to exist :P

mangaroosh, if time didn't exist, then the Universe would just be static, where nothing changes. It'd be like hitting the pause button, surely? Time is a fundamental requirement for the Universe. It simply cannot exist without it.

That is a slightly different topic, and no less interesting [I find personally], but lets imagine that time ceased to exist, how would this be reflected in the General Relativity equations?

Kevster

I dont think that anyone here can answer your question. The best guy to ask is - unfortunately - the 'man' himself (i.e. Einstein). The thing about it is, however, 'time' was a fundamental parameter of those equations, and they are all based on it. If you take out time, then the equations just wouldn't make any sense.

...?

roosh

Kevster wrote: »

I dont think that anyone here can answer your question. The best guy to ask is - unfortunately - the 'man' himself (i.e. Einstein). The thing about it is, however, 'time' was a fundamental parameter of those equations, and they are all based on it. If you take out time, then the equations just wouldn't make any sense.

...?

Cheers, that does go some way to answering the question.

I'm sure though, there must be someone who knows enough about General Relativity still living who could answer the question. At a stretch in this country (and hopefully on this board).

Cheers for the answer though.

Kevster

You're welcome. I actually wouldn't be confident that anyone knows the Relativity equations too well thuogh; and I don't suspect that anyone ever will. Picture how hard it is to read and understand someone else's work, and this particular situation is made worse by the fact that Einstein was a messy writer!

roosh

Kevster wrote: »

You're welcome. I actually wouldn't be confident that anyone knows the Relativity equations too well thuogh; and I don't suspect that anyone ever will. Picture how hard it is to read and understand someone else's work, and this particular situation is made worse by the fact that Einstein was a messy writer!

was he yeah?

there is a book by Julian Barbour called the "end of time". Someone else mentioned it to me. I was just checking it out on Google books. Only read the preface and the first few lines, but sounds like it should be interesting.

anyway, bedtime for me, lad. Thanks again

Kevster

No problem. By the way, Hawkins' A brief history of time should be the first book to read by every newbie cosmologist (that's if you are one).

Edit: Considerin that guy did his PhD theseis on relativity, Id' say he's one of the few who actually understands it to a high degree. That book sounds interesting too, but I don't think his ideas have anjy ounce of practical sense (i.e. in reality) about them. It's always nice to dream though...

Professor_Fink

Kevster wrote: »

I actually wouldn't be confident that anyone knows the Relativity equations too well thuogh; and I don't suspect that anyone ever will.

Oh, come on! It's a major field of study. GR is even an undergrad course on many theoretical physics courses. It's not terribly complicated.

The reason I haven't given a more direct answer is that the question doesn't make a whole lot of sense. Time clearly does exist, so it will never e discovered not to exist.

If you want to ask the question, you need to phrase it in terms of a toy model, not our universe. So, can we have a 3+0 formulation of GR? Sure, but it's very boring. The metric will have signature {+,+,+}, so it will just be Euclidean space. Since there is no time, there is no proper time, and so you have to ditch all the geodesic equations. You're just left with a rather boring static solution to the Field equations.

eZe^

Kevster wrote: »

You're welcome. I actually wouldn't be confident that anyone knows the Relativity equations too well thuogh; and I don't suspect that anyone ever will. Picture how hard it is to read and understand someone else's work, and this particular situation is made worse by the fact that Einstein was a messy writer!

What are you talking about? There is a lecturer in the ucc physics department named Niall O Murchadha who is (apparently) one of the worlds experts in General Relativity. If someone I see nearly everyday can be an expert in the field, I'm sure there are plenty of them out in the big bad world.

If you really want to ask someone who knows the topic, you could try emailing him, but I can see the question just frustrating him as it makes little sense. It's like building a structure made entirely from sand, then asking 'what if sand didn't exist', well... Then the structure wouldnt exist either..

Here's his website anyway if you want to give him a buzz. Don't tell him I recommended you though. Hahaha.

http://www.physics.ucc.ie/people/nom.htm

Kevster

Sorry guys, I guess I just felt obliged to respond to the OP while no-one else was; and that meant basing my answer on what little knowledge I have in this field. My background is biology, which explains things!

roosh

Kevster wrote: »

No problem. By the way, Hawkins' A brief history of time should be the first book to read by every newbie cosmologist (that's if you are one)./quote]

Nope, I'm just a lay person who has a burgeoning interest in a number of areas, including the sciences.

I saw the documentary of the same name, haven't read the book though.

Kevster wrote: »

Edit: Considerin that guy did his PhD theseis on relativity, Id' say he's one of the few who actually understands it to a high degree. That book sounds interesting too, but I don't think his ideas have anjy ounce of practical sense (i.e. in reality) about them. It's always nice to dream though...

when you have "time" at all, some logical investigation into the hypothesis, could yield some interesting insight.

roosh

eZe^ wrote: »

What are you talking about? There is a lecturer in the ucc physics department named Niall O Murchadha who is (apparently) one of the worlds experts in General Relativity. If someone I see nearly everyday can be an expert in the field, I'm sure there are plenty of them out in the big bad world.

If you really want to ask someone who knows the topic, you could try emailing him, but I can see the question just frustrating him as it makes little sense. It's like building a structure made entirely from sand, then asking 'what if sand didn't exist', well... Then the structure wouldnt exist either..

Here's his website anyway if you want to give him a buzz. Don't tell him I recommended you though. Hahaha.

http://www.physics.ucc.ie/people/nom.htm

cheers for that.

might give him a shout for the craic.

Julian Barbour's website shows that Barbour is actually working with Niall O Murchadha, at the moment.

Barbour's website wrote:

During the last few years, I have collaborated with Edward Anderson, Brendan Z. Foster, Bryan Kelleher and Niall Ó Murchadha. I describe our current research programme here . We receive offers of collaboration with interest and can provide some support and supervision to young researchers.

roosh

Just a further question. What evidence is there for the existence of time?

Turtwig

mangaroosh wrote: »

Just a further question. What evidence is there for the existence of time?

Change.
Entropy seems to imply it only has one direction, I think.

roosh

Malty_T wrote: »

Change.
Entropy seems to imply it only has one direction, I think.

That would be one of the things that should be questioned.

Ultimately, the question boils down to whether time is something that exists and is measureable, or whether time is a system of measurement derived from measuring something else.

In what way though would you say that change is evidence for the existence of time?

Professor_Fink

mangaroosh wrote: »

Just a further question. What evidence is there for the existence of time?

You mean other than the fact that things change? That things move? That our perception of the universe has had more than one state?

Of course time is measurable. That's what clocks do.

roosh

Professor_Fink wrote: »

You mean other than the fact that things change? That things move? That our perception of the universe has had more than one state?

Of course time is measurable. That's what clocks do.

Just because we perceive time, it does not necessarily mean that it exists. The earth was perceived as being flat, by some, at one stage, and it was also perceived that the sun revolved around the earth.

I would question how the idea that things change and move is evidence for the existence of time, but one of the main issues, and indeed a primary assumption that needs to be questioned is whether or not a clock actually measures time.


Closer examination would suggest they don't. For example, what the original 24hr clock were measuring was not actually time, rather the degree of rotation of the earth. The degree of rotation was assigned a value of seconds, minutes, hours and a full rotation was called a day.

So there, it is not time that is actually measured, rather the degree of rotation of the earth.


With the current atomic clocks, again it is not time that is measured. What the measurement device actually measures is the microwave emissions of changing electrons.

This is then taken as a unit of measurement, what we call time. However, it is not time that has actually been measured.

Professor_Fink

mangaroosh wrote: »

Just because we perceive time, it does not necessarily mean that it exists. The earth was perceived as being flat, by some, at one stage, and it was also perceived that the sun revolved around the earth.

Many of the physical definitions of time simply amount to "Taht which clocks measure". Given that clocks measure something, hence time exists.

mangaroosh wrote: »

Closer examination would suggest they don't. For example, what the original 24hr clock were measuring was not actually time, rather the degree of rotation of the earth. The degree of rotation was assigned a value of seconds, minutes, hours and a full rotation was called a day.

So there, it is not time that is actually measured, rather the degree of rotation of the earth.

The degree of rotation of the earth? First, no, this is not what most clocks do. Second, rotation implies motion which implies the existence of time.

mangaroosh wrote: »

With the current atomic clocks, again it is not time that is measured. What the measurement device actually measures is the microwave emissions of changing electrons.

This is then taken as a unit of measurement, what we call time. However, it is not time that has actually been measured.

Emission again implies change with respect to time, and hence the existence of time.

There is no 'time' observable, so you need to measure time via some change in another operator, but it is nonsense to claim that time doesn't exist. It's implicit in the very language we are using to have the conversation.

roosh

Just wanted to link to a similar discussion on the existence of time in the philosophy forum.

Professor_Fink

mangaroosh wrote: »

Just wanted to link to a similar discussion on the existence of time in the philosophy forum.

Seriously, this is a ridiculous conversation to be having. I suspect, and hope that you mean something a little deeper than what you are actually saying, but simply proclaiming time not to exist is ridiculous, since it effectively is defined in such a way that it must exist if we exist. Asking whether we exist may be philosophically interesting, but is completely non-constructive and has no place on a physics forum.

Fringe

mangaroosh wrote: »

Just wanted to link to a similar discussion on the existence of time in the philosophy forum.

Why are you trying to complicate something so much? Time clearly exists because we can perceive change. You're trying to speculate that it doesn't exist but there's no evidence that points towards this. That thread has to much speculation and nothing definite. (like that guy talking about time being a form of energy) Time is so fundamental to everything that it has to exist.

roosh

the question is ultimately:

does time exist as "something" that can be measured, or is it a system of measurement, created by man?


it appears that time is treated as something which can be measured, and it is asserted that clocks measure time.

However, closer examination shows that the concept of time only arises as an attempt to rationalise our observation of change. It ultimately involves a comparison of non-reality with reality.


If we take an atomic clock for example. What we have is a measurement device that measures the microwave emissions of changing electrons.

Therefore, what is being measured is the microwave emissions of changing electrons. It is not "time" that is being measured, rather the phenomenon that is being measured is designated as a unit of the measurement sysytem called time.


The measurement system is similar in nature, to the metric system. It is an invention of mankind and does not exist in reality.



So far such things as motion, life and change have been proposed as evidence for the existence of time, however, it is theses subjective interpretation of these phenomena, that actually give rise to time, or that have lead man to create the concept of time.


Is there an explanation for how motion and change are evidence of time?

Morbert

mangaroosh wrote: »

the question is ultimately:

does time exist as "something" that can be measured, or is it a system of measurement, created by man?

it appears that time is treated as something which can be measured, and it is asserted that clocks measure time.

However, closer examination shows that the concept of time only arises as an attempt to rationalise our observation of change. It ultimately involves a comparison of non-reality with reality.

If we take an atomic clock for example. What we have is a measurement device that measures the microwave emissions of changing electrons.

Therefore, what is being measured is the microwave emissions of changing electrons. It is not "time" that is being measured, rather the phenomenon that is being measured is designated as a unit of the measurement sysytem called time.

The measurement system is similar in nature, to the metric system. It is an invention of mankind and does not exist in reality.

So far such things as motion, life and change have been proposed as evidence for the existence of time, however, it is theses subjective interpretation of these phenomena, that actually give rise to time, or that have lead man to create the concept of time.

Is there an explanation for how motion and change are evidence of time?

What would be the difference between a universe with 'actual' time, and a universe where time merely represents change? How would, say, simultaneity effects be different?

Either way, it doesn't really matter with General Relativity. General Relativity is not a theory of what time is. Instead, it's a theory of how it (among other things) behaves. So, whether or not time is intrinsic, or a convenient representation of change, time still obeys the rules of Relativity.

Kevster

'Time' is just a concept that we have created to describe the world around us, just as language is. It's not real in any physical sense. It's just a concept. The Universe doesn't care less for time as it would care for a force like gravity, for example.

Turtwig

Kevster wrote: »

'Time' is just a concept that we have created to describe the world around us, just as language is. It's not real in any physical sense. It's just a concept. The Universe doesn't care less for time as it would care for a force like gravity, for example.

Em, GR kinda relies on time being physical in some sense anyways.

Kevster

That's maths though, which isn't reality. Maths is a best approximation of what our reality is (and will be). Time really isn't a physical concept... use your brain and think about it. The notion of time - I believe - introduces it's own problems into GR, such as the necessity for a beginning of time (i.e. Big Bang).

Morbert

Kevster wrote: »

That's maths though, which isn't reality. Maths is a best approximation of what our reality is (and will be). Time really isn't a physical concept... use your brain and think about it. The notion of time - I believe - introduces it's own problems into GR, such as the necessity for a beginning of time (i.e. Big Bang).

Even if time emerges from change, it is still a physical concept, just as length or height is a physical concept. The difficulty with relativity is not related to the ontology of time. Instead, it's related to the formalism, and how that formalism compares to the formalism of quantum mechanics.

I'm all for investigating the nature of time. But if it doesn't produce a new formalism then it isn't much use to scientists. Scientists are less interested in questions like "Does time exist?" and more interested in questions like "Should we treat time as a dynamical variable?"

Vergast

'Time' is just a concept that we have created to describe the world around us, just as language is. It's not real in any physical sense. It's just a concept. The Universe doesn't care less for time as it would care for a force like gravity, for example.

No, the universe most definitely needs time and gravity. Without gravity there would be no universe! Hell if any of the 4 forces were much different from thier current values then god only know what would have happened.

Turtwig

Vergast wrote: »

No, the universe most definitely needs time and gravity. Without gravity there would be no universe! Hell if any of the 4 forces were much different from thier current values then god only know what would have happened.

I think there was something recently about the electro-weak force not being needed. Not sure of how well accepted this idea is though.:)

Kevster

Vergast wrote: »

No, the universe most definitely needs time and gravity. Without gravity there would be no universe! Hell if any of the 4 forces were much different from thier current values then god only know what would have happened.

You misinterpreted what I wrote: I implied that the Universe doesn't need time and that it does need gravity. However, I can see now why time is important. Due to what Morbert wrote three posts up, I have changed my opinion about it (time).

roosh

looks like we could have a decent debate on our hands here too

Morbert wrote: »

Even if time emerges from change, it is still a physical concept, just as length or height is a physical concept.

The thing is however, that time emerges from change in much the same way that the concept of the earth being flat, emerged from a limited and incorrect interpretation of the earth, or the same way that the concept of the sun orbiting the earth emerged.

Morbert wrote: »

The difficulty with relativity is not related to the ontology of time. Instead, it's related to the formalism, and how that formalism compares to the formalism of quantum mechanics.

it has been purported, by Julian Barbour in "End of time" - among others - that the "problem of time" between QM and GR is resolvable, when time is considered to be non-existent.

Morbert wrote: »

I'm all for investigating the nature of time. But if it doesn't produce a new formalism then it isn't much use to scientists. Scientists are less interested in questions like "Does time exist?" and more interested in questions like "Should we treat time as a dynamical variable?"

Not entirely sure what kind of formalism may arise, but if it were to be considered in the same sense that measurements are considered e.g. centimetres, metres, etc.

It appears that Barbour and Niall Ó Murchadha(among others) are currently working on a Research Project with regard to the non-existence of time and its impact on General Relativity.

Kevster

mangaroosh wrote: »

The thing is however, that time emerges from change in much the same way that the concept of the earth being flat, emerged from a limited and incorrect interpretation of the earth, or the same way that the concept of the sun orbiting the earth emerged.

I think that it's a bit unfair to compare this minor debate on time with the much earlier theories on the position of the Sun and the shape of the Earth. They aren't really comparable, and any comparison is therefore false/unfair. If you are merely saying, however, that what has been commonly regarded as the truth before has been debunked later on, then I see your point. Still, I can't see 'time' being extracted from any cosmological equations for a long time. It's a fundamental concept.

Fringe

Interesting. I think I'm understanding your point a bit more now. I think though, regardless of its existence or not, we still experience time as an effect and our theories are consistent with this effect. For example, in a rotating reference frame, we experience centrifugal/coriolis forces but these do not really exist in a way yet we acknowledge their effect. In the same way, time exists because it has an effect on us.

Morbert

mangaroosh wrote: »

The thing is however, that time emerges from change in much the same way that the concept of the earth being flat, emerged from a limited and incorrect interpretation of the earth, or the same way that the concept of the sun orbiting the earth emerged.

This is a very large claim. It may turn out to be true, but to show that it is true, you would need a "timeless" formalism of the laws of physics which explain phenomena that current formalisms can't. Until then, while I certainly won't dismiss it, I won't accept it either.

It has been purported, by Julian Barbour in "End of time" - among others - that the "problem of time" between QM and GR is resolvable, when time is considered to be non-existent.

It appears that Barbour and Niall Ó Murchadha(among others) are currently working on a Research Project with regard to the non-existence of time and its impact on General Relativity.

A different treatment of time may yield fruitful results, and a timeless theory of quantum gravity has its advantages, though it's important to qualify what they mean by timeless. From what I gather, Barbour's work is closely linked to the ADM formalism of General Relativity, where local time-evolution can apparently be determined by a structure of foliated spacelike "moments". Time lapse, in other words, emerges from such structures. It is certainly exciting work, but it doesn't "kill" time in the manner you seem to be inferring. Nor has it yet solved the problem of quantum gravity. Quantization is still an issue, and there are approaches that don't treat time in this manner which are just as potentially valid.

Kevster

Sorry to slightly deviate, but if 'time' is something that is real, then shouldnt' we be able to manipulate it? I still hold the view that it's merely a 'figment of our imagination' - i.e. a concept and consequence of mere language and thought - and that it's simply something that can never be altered.

I mentioned earlier at how the introduction of a time variable necessitates the need for a beginning and end. Our brains cannot seem to interpret that there was 'always' a Universe. We rthink in terms of time and this requires a start/end.

...thoughts?

Kevin

Podge_irl

Kevster wrote: »

Sorry to slightly deviate, but if 'time' is something that is real, then shouldnt' we be able to manipulate it? I still hold the view that it's merely a 'figment of our imagination' - i.e. a concept and consequence of mere language and thought - and that it's simply something that can never be altered.

Can people manipulate space? Anything you do to "manipulate space" - i.e., curve it or bend it, also has an effect on time.

Our brains cannot seem to interpret that there was 'always' a Universe. We rthink in terms of time and this requires a start/end.

I'd argue the opposite. People seem to have an issue with dealing with nothingness and are prone to asking questions such as "what happened before the bang", even if such questions don't make sense.

Morbert

Kevster wrote: »

I mentioned earlier at how the introduction of a time variable necessitates the need for a beginning and end. Our brains cannot seem to interpret that there was 'always' a Universe. We rthink in terms of time and this requires a start/end.

Just to clear up some possible confusion. GTR is already, in a sense, timeless, as the spacetime manifold "always" exists. Time, according to relativity, is simply a dimension, like space, and time-evolution is determined by timelike paths through spacetime. What Barbour is suggesting is removing time as a dimension and re-introducing it as a parameter deriveable through local spatial variables.

Myrddin

Isnt it proven, that the faster something approaches light speed, that the passage of time changes for that object relative to a stationary object? (Relativity)

If so, then isnt time then proved as existing? Its nature changes, given interaction. It might be our definition of time which is right/wrong, but it is a reality of sorts, which is intertwined with space.

roosh

Kevster wrote: »

I think that it's a bit unfair to compare this minor debate on time with the much earlier theories on the position of the Sun and the shape of the Earth. They aren't really comparable, and any comparison is therefore false/unfair. If you are merely saying, however, that what has been commonly regarded as the truth before has been debunked later on, then I see your point. Still, I can't see 'time' being extracted from any cosmological equations for a long time. It's a fundamental concept.

apologies, the tone may have been somewhat derogatory, but they are meant to be taken as illustrative examples.

essentially the concept of time arises out of a misperception of our obeserved environment.

roosh

Morbert wrote: »

This is a very large claim. It may turn out to be true, but to show that it is true, you would need a "timeless" formalism of the laws of physics which explain phenomena that current formalisms can't. Until then, while I certainly won't dismiss it, I won't accept it either.



A different treatment of time may yield fruitful results, and a timeless theory of quantum gravity has its advantages, though it's important to qualify what they mean by timeless. From what I gather, Barbour's work is closely linked to the ADM formalism of General Relativity, where local time-evolution can apparently be determined by a structure of foliated spacelike "moments". Time lapse, in other words, emerges from such structures. It is certainly exciting work, but it doesn't "kill" time in the manner you seem to be inferring. Nor has it yet solved the problem of quantum gravity. Quantization is still an issue, and there are approaches that don't treat time in this manner which are just as potentially valid.

I'll have to hold my hands up and say that I wouldn't have much of a clue how it would affect any of the scientific theories, so apologies for just regurgitating what I have read myself.

I know I asked the question with regard to General Relativity, but that was largely because of my perception of how time is handled in General Relativity. It appears that it is given some intrinsic existence, as making up "the fabric of reality", as opposed to being a man made concept.


The core question is on the existence of time, whether it is a real "thing" or just a human concept. Again, the contention is that it is just a human concept based on our perception of the universe.

I presume this would have some impact on those scientific theories that treat time as though it exists in reality, although I am not in a position to say what that would be, exactly.

roosh

EnterNow wrote: »

Isnt it proven, that the faster something approaches light speed, that the passage of time changes for that object relative to a stationary object? (Relativity)

If so, then isnt time then proved as existing? Its nature changes, given interaction. It might be our definition of time which is right/wrong, but it is a reality of sorts, which is intertwined with space.

Is it time dilation that is referred to above?

Kevster

Also in response to that (what EnterNow said), is that anything to do with the 'twins' paradox? - i.e. where if one twin grew up on Everest and the other at ground level, the one on Everest would age quicker? I never understood this in any sense.

Morbert

Yes, that is time dilation. Electromagentism demands that everyone observes the speed of light to be "c". This is only possible if we discard the notion that time has a fixed rate of passage for everyone.

As for the twin paradox: A twin on everest would age more, but typically speaking, the twin paradox is normally presented with one twin travelling a great distance and returning to earth, while the other twin remains on earth. According to relativity, the passage of time acts somewhat like an odometer for our journey through spacetime. The longer a path through spacetime, the more time experience by someone on that path. The geometry of spacetime is a weird kind, called "pseudo-riemannian", and it tells us, oddly enough, that the twin that stayed on earth actually travelled a longer path through spacetime, and hence experienced more time, than the twin that left earth and came back. The reason it's called a paradox is there are some issues with the symmetry of time dilation that take a little thinking to overcome.

There are other strange features of relativity as well, like simultaneity. To use Roger Penrose's example, in my "now" an alien fleet could be on their way from the andromeda galaxy to take over earth, while in your "now" they could still be debating amongst themselves whether to invade earth. All of these features fall out of the geometry of spacetime described by relativity.