Modes of Time

[Mr Spinkles]

Ok, moving on. 4 dimensional spacetime consists of 3 dimensions of space plus one dimension of time. Lets imagine that you and I decide to meet somewhere in New York City. So how many points of information would you have to give me (or I give you) to insure that we do actually meet? Well you could give me the location that you intend to meet me, the longitude(1) and latitude(2) and since New York contains many tall buildings you might also have to tell me what floor to go to – height(3). So there are three coordinates that refer to the three dimensions of space. But obviously this is not enough information, you will also have to tell me what time(4) you want to meet. So there you have time being the fourth dimension of spacetime. Every point in our four dimensional universe* can be defined by four coordinates.

Well said, however the fact that we need four coordinates (x,y,z,t) to locate an event was true in classical physics before Einstein, this goes back to Galileo and is called Galilean relativity.

In this case, the "normal" case we are all intuitively familiar with, x,y,z,t in one reference frame S is related to x',y',z',t' of another reference frame S' in a simple and intuitive way. E.g. if the reference frames are at rest relative to each other, and they are oriented the same way, and they are separated by a distance X along their x-axes, then x' = x + X. Of course if the reference frames are moving relative to each other and accelerating and rotating, the equations may not seem so "simple" but you can nevertheless figure it out, step by step, using your intuition of the geometry of space and drawing pictures.

We are all familiar with the consequences of Galilean relativity. For example two racecars that are neck-and-neck may be going 100 mph, around in circles, in a reference frame fixed to the grandstand. However, in a reference frame fixed to one of the racecars, both racecars are stationary and separated by a small distance and the grandstand is going around in circles.

Another example: the length of some object is always the same in a Galilean (intuitive) reference frame even if they are moving relative to each other in complex ways.

The counter-intuitive thing about Einstein's Relativity is that the coordinates x,y,z,t in one reference frame are mixed up, and related in a strange way to the coordinates x',y',z',t' in a different reference frame. This is one thing that was truly different about Relativity, and it leads to conceptually bizarre consequences that you would be very unlikely to work out by drawing diagrams and using your intuition.

Here's one striking example of relativity, the curvature of space at large scales causes the light from galaxies in this deep space photo to be distorted. Galaxy Cluster Abell 1689

 

[kai]

OK everyone who thinks time is on a clock, turn and follow me and ---RUN

 

[Mr Spinkles]

Then how do you explain Einstein's theories? There was NO experimental evidence leading to the Theory of Relativity and space also being time. He came up with it completely out of the blue and put it on a chalkboard, hardly experimental.

Well that's not quite true. And remember what I said was:

The most important thing to understand relativity is to examine the results of physics experiments. The results are strange. Strange results sometimes require strange explanations.

I'm not saying this is how Einstein came up with Relativity, I'm saying this is the reason we have to accept it (as far as we accept any well-evidenced theory) and the key to understanding it. The best way to understand a concept is not always by taking the same route through which it was discovered. If we take that route we will quickly get bogged down in confusion and a million ideas that seem promising, but are a waste of time. It's better to start out with the hindsight of 100 years of experiments to guide our thoughts.

In a nutshell, a brief explanation of the history of Relativity:

1. 19th century experiments with electromagnetism (EM) produce strange results, several laws, rules and equations work; eventually Maxwell's 4 equations of EM generalize and explain all EM
2. In addition to explaining the experimental results of EM, Maxwell's equations also predict that in some circumstances the EM field can produce waves that propagate at speed C, related to constants measured by EM experiments. This is also the measured speed of light (the kind we see). It is realized the light we see is an EM wave.
3. EM waves are produced in wire with an oscillating current which can be "picked up" and induce an oscillating current in another wire some distance away. (Hence radio) This confirms the predictions of Maxwell's equations and shows radio waves are just EM waves, like light, that are not visible to the eye. (Same is found with X-rays).
4. There is confusion as to why the speed of an EM wave should equal C* regardless of the reference frame in which its speed is measured. Lorentz works out some algebraic relationships ("transformations") between x,y,z,t and x',y',z',t' of different reference frames which, unlike the Galilean relationships, are compatible with the condition that the speed of light, C is constant in all frames. There is difficulty giving a physical interpretation of this.
5. Einstein gives it a physical interpretation by working out the measurable consequences of the Lorentz transformations and proposing experiments which would test those consequences.
6. Experiments test the consequences for 100 years and Einstein is right on the money. Global positioning, NASA communicating with far-away satellites, atomic clocks, high-energy particle physics, the red-shift and the expansion of space -- all of these lines of inquiry give numerical measurements. These measurements are remarkably well described by Relativity and not even intelligible by the lights of Galilean relativity.

So that's essentially how Relativity came about, briefly. We can argue about what was more important historically, theory or experiment, *personally I think it's like walking, each foot takes turns leading the way. But if you want to understand Relativity you don't necessarily need to adopt the historical route as I said. Better to start with what we know from experiment, now.

*edit: actually I believe I heard that analogy somewhere else, I think it was a physicist named Rabi. Or Feynman.
*edit: In case you are interested, the speed of light C = 3x10^8 meters/second. Please notice that this is very strange because it just has a "speed" that is true in all reference frames. If you are in a boat you can see dolphins pass by, you can increase your speed to catch up to them and ride alongside them. Not so with light. It would be as if the dolphins always increase their speed just enough to maintain a certain speed relative to your boat. And yet the same dolphins are moving at that same speed relative to the stationary boats. This is a very strange fact that demands a strange explanation.

 

[themadhair]

And so I ask you, how did Einstein come up with his idea of Space/Time with absolutely NO experimental evidence suggesting it?

Time is not space. The previous two posters gave a good explanation of this.

Constancy of the speed of light in all inertial frames? The orbit of Mercury? These are experimental results that Einstein used to develop his theory. IIRC the orbit of Mercury forced Einstein back to the drawing board a few times before he finally nailed it.

But you go ahead and beat those two falsehoods some more.

 

[Francis]

Heh heh he... It was funny, 'cause when i was reading the wikipedia link, i let out a big, "Oh!". the whole space time thing just sorta clicked. I skipped most of it though, 'cause it got into heavy math and whatnot that sounded boring. But i now get it! Peace!

 

[Ben Dhyan]

Can someone explain spacetime to me? "Time is the fourth dimension of space," but what the hell does that mean?! It just doesn't make sense to me. I don't reject it, for that very reason, but I'm sorely tempted because it strikes me as utterly nonsensical.

First off, is spacetime a theory, or a hypothesis? If the former, how in the world was it tested?

Anyway, even if it's true, it seems to me that there would be two different modes of time. Spacetime, and linear progression. There was still something before the Big Bang.

Hi Storm, FWIW, here is my present understanding

Time is a merely a concept that implies the persistence of the awareness of existence. There is no existence without awareness and no awareness without existence for they are complementary opposite concepts of non-duality.

The mortal mind can not conceive of non-duality for it (mind) functions on a dualistic basis by evolutionary design, so it abstracts from the non-duality of reality the complementary opposite concepts of infinity (space) and eternity (time).

So the space-time concept is one that tries to put non-duality in a dualistic framework so the mortal mind can deal with it. However the fact is that there is no time without space and no space without time for they are mere complementary opposite of one, i.e. non-duality. When the mind is tranquil, the concept of space and the concept of time merge as unity.

So space (infinity) and time (eternity) for dualistic mortal mind expediency are conceived and then considered as separate finite cosmic qualities, and become measurable quantities for endless scientific theorizing.

When the concept of finiteness is abstracted from the non-duality (the underlying unity of space and time), then the requirement of a beginning and ending of the non-duality naturally follows in the workings of the dualistic mortal mind so the 'big bang' theory is hypothesized.

With true understanding, the unity of all is seen as that represented by the concept of non-duality, and is that which never had a beginning, nor will it ever have an ending, and all the ceaseless creative and destructive forces at work in the cosmos were, are, and always will be mere complementary harmonizing attributes of this non-conceptual unity. When true understanding is lacking, mortal dualistic understanding hypothesizes all sorts of scientific theories based on finiteness, and creates 'reality' for those who allow themselves to be conceptually attuned to this popular mortal contemporary anthropocentric understanding of reality.

 

[linwood]

Here's one striking example of relativity, the curvature of space at large scales causes the light from galaxies in this deep space photo to be distorted. Galaxy Cluster Abell 1689

Nonsense.

This isn`t an example of the "curvature" of space.

This is an example of the effects of gravity on photons.

Calling this a "curvature" of space is disingenuous however common the practice is.

It gives the layman the wrong idea.

 

[themadhair]

Nonsense.

This isn`t an example of the "curvature" of space.

This is an example of the effects of gravity on photons.

Calling this a "curvature" of space is disingenuous however common the practice is.

It gives the layman the wrong idea.

I agree with this. Outside of mathematical equations it doesn’t really make any sense to talk about the curvature of spacetime.

 

[Alceste]

Can someone explain spacetime to me? "Time is the fourth dimension of space," but what the hell does that mean?! It just doesn't make sense to me. I don't reject it, for that very reason, but I'm sorely tempted because it strikes me as utterly nonsensical.

First off, is spacetime a theory, or a hypothesis? If the former, how in the world was it tested?

Anyway, even if it's true, it seems to me that there would be two different modes of time. Spacetime, and linear progression. There was still something before the Big Bang.

Actually, it is linear time that is nonsensical. If you have to discard one or the other, make it that one.

To answer your question, "spacetime" a mathematical model with practical applications in physics because it appears to accurately describe the behavior of the universe and predicts phenomenon that occur. Gravity slows time down, and time is also affected by the observer's speed of travel (i.e. the closer she gets to the speed of light, the slower time goes).

In the context of the Big Bang, we can speculate that since intense gravitational fields slow the rate at which time passes, and the singularity from which the universe erupted would have been infinitely dense, there would not have been any passing of time.

Or, you can think about it this way, there is no such thing as "time" on its own. It has always been a construct that is inseparable from the physical universe. The only meaningful measure of it is that we (humans) have is not linear. I.e. the earth's orbit around the sun, the earth's rotation, the phases of the moon. Which of these represents this "linear progression" you talk about? Imagining for a moment that the planets and stars do not exist, what is "time"? And imagining for a moment that there is no consciousness present to retain the memory of "before" and the anticipation of "after", where in the cosmos is there anything that progresses in a straight line? Even light bends, and all of us remember things that didn't happen and expect things to happen that never will.

 

[Magic Man]

I agree with this. Outside of mathematical equations it doesn’t really make any sense to talk about the curvature of spacetime.

Why? And why is space said to be curved by physicists like Hawking, then? Also, how do wormholes work, if space is not curved?

(I'm not claiming to be an expert, this assertion by you and Linwood just struck me as odd. I could be missing something, though.)

 

[themadhair]

Why? And why is space said to be curved by physicists like Hawking, then? Also, how do wormholes work, if space is not curved?

(I'm not claiming to be an expert, this assertion by you and Linwood just struck me as odd. I could be missing something, though.)

AFAIK the reason spacetime is thought of as being curved follows from the use of geodesic in the mathematics. But because the mathematics involves constructs that were developed for distance mapping across different geometries doesn’t necessarily mean that what is being modelled us curved in the geometrical sense. For example, does the use of elliptical curves in prime number algorithm mean that there are elliptical prime numbers?

Think of it this way. We have developed mapping systems for use on the earth that account and compensate for its spherical nature. The earth is curved because we can point to the thing and see that it is curved from the construct of a planer surface. Can we really do that for spacetime? Particularly when it isn’t really clear yet what exactly spacetime even is?

 

[Alceste]

AFAIK the reason spacetime is thought of as being curved follows from the use of geodesic in the mathematics. But because the mathematics involves constructs that were developed for distance mapping across different geometries doesn’t necessarily mean that what is being modelled us curved in the geometrical sense. For example, does the use of elliptical curves in prime number algorithm mean that there are elliptical prime numbers?

Think of it this way. We have developed mapping systems for use on the earth that account and compensate for its spherical nature. The earth is curved because we can point to the thing and see that it is curved from the construct of a planer surface. Can we really do that for spacetime? Particularly when it isn’t really clear yet what exactly spacetime even is?

AFAIK, we have observed the curvature of spacetime, for the bending of starlight during a solar eclipse.

Our little monkey brains think in terms of flat surfaces and straight lines only because they're simple to measure, and we are stupid. There are no straight lines and flat surfaces in reality.

 

[themadhair]

AFAIK, we have observed the curvature of spacetime, for the bending of starlight during a solar eclipse.

I thought that was the gravity?

Snarky comment aside, do the equations of general relativity map the movement of light and mass under gravity or do they map spacetime? From my general relativity classes I’d have to say it’s the former. The curvature of spacetime rubber-sheet analogy works for describing the effects of gravity – but if it really does follow from the equations then I’ve yet to see it.

 

[Alceste]

I thought that was the gravity?

Snarky comment aside, do the equations of general relativity map the movement of light and mass under gravity or do they map spacetime? From my general relativity classes I’d have to say it’s the former. The curvature of spacetime rubber-sheet analogy works for describing the effects of gravity – but if it really does follow from the equations then I’ve yet to see it.

I believe it is thought to be gravity acting on spacetime. Or spacetime being affected by gravity, with the visible consequence of light bending. Or something.

I'm not being snarky, we really are too stupid for this stuff, and the complexity of the mathematical equations we are able to consciously comprehend is severely limited by our puny little monkey brains. Most of us, anyway. I'm in the 99th percentile according to those IQ tests they make you take in school - an IQ of 160 according to the internet (which as we all know is infallible when it comes to IQ assessment), and I'm happy to admit I'm much too stupid for things like string theory.

 

[linwood]

I really didn`t want to get into this yet again but I`m a glutton for punishment.

Actually, it is linear time that is nonsensical. If you have to discard one or the other, make it that one.

No thanks, I`ll take reality over mathematics thanks.

Gravity slows time down, and time is also affected by the observer's speed of travel (i.e. the closer she gets to the speed of light, the slower time goes).

Gravity does not "slow time down".
Gravity affect the devices we use to measure time.
It slows them down.

In the context of the Big Bang, we can speculate that since intense gravitational fields slow the rate at which time passes, and the singularity from which the universe erupted would have been infinitely dense, there would not have been any passing of time.

"Infinately dense" is an impossibility in the physical universe of matter and energy that we know.
The "singularity" in the popular Big Bang model is an invention of an imaginative mind.

 

[Alceste]

I really didn`t want to get into this yet again but I`m a glutton for punishment.

No thanks, I`ll take reality over mathematics thanks.

Gravity does not "slow time down".
Gravity affect the devices we use to measure time.
It slows them down.

Hi, Linwood, just a couple questions -

How exactly do you feel "reality" works differently from the way physicists and mathematicians tell us it works?

Are you defining light as a "time-measuring device"?

"Infinately dense" is an impossibility in the physical universe of matter and energy that we know.
The "singularity" in the popular Big Bang model is an invention of an imaginative mind.

What would you consider to be a more accurate alternative theory?

IMO, you need to be incredibly imaginative to be able to conceptualize the whole universe/ multiverse, and even more imaginative for your speculations to result in empirical supporting evidence, but that's just an opinion.

 

[themadhair]

I believe it is thought to be gravity acting on spacetime. Or spacetime being affected by gravity, with the visible consequence of light bending. Or something.

And where, pray tell, does this exist in the equations of GR? Genuine question.

 

[themadhair]

How exactly do you feel "reality" works differently from the way physicists and mathematicians tell us it works?

GR exists in the equations – and nowhere in those equations is there a modelling of curve spacetime. If I am wrong then kindly point this out to me.

And for the record, I strongly object to your claim that me and linwood are disagreeing in the manner you are insinuating.

 

[linwood]

How exactly do you feel "reality" works differently from the way physicists and mathematicians tell us it works?

I`d have to show you one of the labor reports put out weekly by my companies accountants to provide example of how mathematics can defy reality when used by a skilled mathematician.

Are you defining light as a "time-measuring device"?

No but it can be used as such.
From what I understand light is comprised of nearly matterless particles travelling through space.

What would you consider to be a more accurate alternative theory?

A more accurate theory would simply be "We don`t know but we mean to find out."
Our physicists should stop postulating "hypothesis" as "theory" to the general public considering the general public already seems to have great difficulty understanding exactly what a "theory" is

IMO, you need to be incredibly imaginative to be able to conceptualize the whole universe/ multiverse, and even more imaginative for your speculations to result in empirical supporting evidence, but that's just an opinion.

I share your opinion Alceste, always have.
The commonly accepted scientific ideas of the origin of the universe seem nearly as imaginative as the story of Genesis to me.



Time does not exist as a material thing.
It is a concept of measurement used by humans to measure one historical event in regards to another using arbitrary time intervals.

Rovelli has been working with one of the world’s leading mathematicians, Alain Connes of the College of France in Paris, on this notion. Together they have developed a framework to show how the thing we experience as time might emerge from a more fundamental, timeless reality. As Rovelli describes it, “Time may be an approximate concept that emerges at large scales—a bit like the concept of ‘surface of the water,’ which makes sense macroscopically but which loses a precise sense at the level of the atoms.”
Newsflash: Time May Not Exist | Einstein | DISCOVER Magazine

"Time" is a concept.

 

[Alceste]

And where, pray tell, does this exist in the equations of GR? Genuine question.

I don't know. The equations in physics are over my head. But this article isn't too bad: black-holes.org—Gravity and Warped Spacetime