Does Time Expand in All Directions in the Universe?

[Spourk]

Spourk, in your image you are are cutting out the time direction entirely. You are also cutting out third space dimension, and leave only 2D image. This is not what I mean.

In pictures 1,2,3 the left and right always seem to point in 'one direction' for the line.
In pictures 4, 5 and 6 up and down always seems to point in 'one direction' for the paper.
in pictures 7, 8, 9 future and past would also always seem to point in 'one direction' for the space.

But any third observer would be wiser.

Hovering above a star to observe planet's orbital path is hardly a 2D image... and my point in the first place is that time doesn't move in a direction. What I tried to do was explain what I think is confusing you about the direction of time, which included all 3 spatial dimensions moving through a 4th time dimension, (which itself isn't moving in a direction).

 

[petm1]

Time dilates in every direction. I may be able to talk about the expansion rate of space between two or more objects with two or more directions between them but I would also be correct to speak of space as a single entity dilating in time. Space and time are two ways we use to describe the same thing with the motion within space being visible and the motion of time not so. Think of our visible universe as a affine space that is always dilating and every single thing has the same motion, outward. I do not see matter dilating but I do exist as a single part of a accelerated frame we call Earth also I do not see the motion of a photon I see it as a color yet to explain each I do need time. A clock may count its own simultaneous existence as a clock but the ticks measure the difference between simultaneous moments we see via photons. For this reason I think of time as all directions for they all exist in time with the same motion, keep in mind that all motion I see is twisted within a focal point from the three dimensions of space's outward motion into the pseudo time of inward motion i think of as my present.

 

[WannabeNewton]

What you have said is just word salad. If you can express your thoughts mathematically then please do so, otherwise you are just uttering nonsense.

 

[Whitefire]

WannabeNewton, I believe that even without mathematic symbols one can express ideas logically and meaningfully.

Spourk, I feel depressed by the way you interpret my words. "you'd get a picture of a blue ring around the sun" is a 2D picture and you cannot represent time/change in 2D without representing velocity. That is why all my representations of time have arrows and why I am talking about directions. Yes they are not merely directions of our '3D' space as we understand it from every day life. But there is just no other word for it. If you really want to make sense of your example, you would 1) need to consider something much larger than Earth and Sun; 2) notice that as you were observing your 'Earth's' movement, it would seem to move slower in the distant fragments of its orbit (relative to you), and faster when near you. You can delete the sun from the picture. In relation to sun, this effect has no meaning, because the sun is always generally the same distance from Earth. Plus 3) I am not sure if this would really happen, even if these were galaxies, not planet and star, because gravity seems to mess with the whole idea.

@Mordred: I thank you but I grasp the concept of light cones quite well. Believe or not but I have imagined light's progress in time as a (very flattened) "X" long before I saw the name 'light cone'. It is a very useful tool, but you are probably aware of the fact that light cones are also relative, meaning that in reality a light cone for point A is different than the light cone for point B. And what I am talking about here is simply (?) relativity, so light cones are only so much useful. You cannot take a single picture, a 'lightlike' image of the universe, and try to deduce how time works from that.

For relativity, you really, really need the third observer. Forget about how you percieve time. Forget about how time passes for other objects relative to you. You need to observe how objects relate to each other.

Perhaps the discussion is not as meaningful as I thought. I have a very specific understanding of spacetime and perhaps you are just used to picture it differently. I see time dilations as movements in specific direcitions, and it's that simple.

This kind of thinking can generate, however, some interesting thoughts. For example, I quite taken by an idea that as space expands, time contracts, and we are not going to have an infinite amount of it. If there was a Big Bang, then there perhaps will be a Big End ---perhaps a Big Freeze, but I would not really bet it is the same. In the Big End we would have the galaxies actually being torn apart by the same process which we now refer to as 'accelerated expansion of the universe', then matter itself being destroyed, and time coming to a stop... or a 'middle', if I am correct...

Good night :)

 

[Popper]

I recently had this idea (which perhaps is not a new one, but I have never heard of it), that on the scale of the entire universe, time expands in all directions at once.

That statement has no meaning since direction is a concept that pertains only to spatial relationships and not to temporal ones.

If we look around us, we generally understand time as 'direction of changes' ….

Who are “we”? Certainly not physicists who do not assign any kind of notion to time as having a “direction.”

And the only sense that one can give to time being orthogonal to space is a mathematical one, not a physical one. Take the spacetime physics that one works with in special relativity as an example. In spacetime physics one uses 4-vectors which reside in spacetime. The mathematical meaning to orthogonal uses the inner product between 4-vectors. When the inner product is zero then the vectors are said to be orthogonal. But the meaning of orthogonal in this context is different than in Euclidean geometry. For example; in spacetime physics the 4-momentum of a photon is orthogonal to itself because the inner product of the 4-momentum of a photon with itself is zero.

The dimension of time is orthogonal to the dimensions of space.

That is incorrect. In the first place it’s mathematically incorrect to speak of a dimension as being orthogonal to something. It’s only meaningful for a 4-vector, or a spatial/temporal axis to be orthogonal to each other. And only then does it have a mathematical meaning, not a physical one.

Yes, time has a direction, but that direction is not up or down, left or right, forward or backward.

That is incorrect. Time does not have a direction. Direction is only something that pertains to spatial relations, not temporal ones. Only when one draws these things on a piece of paper do they actually have physical direction.

Direction quite literally only pertains to spatial directions, not temporal ones. However one does speak of them as having such thing but that’s merely for purpose of visualizing objects in spacetime is that done. There is no physical meaning to it.

 

[WannabeNewton]

That is incorrect. Time does not have a direction.

This is a very broad statement that is incorrect in and of itself. See here:

Note that for a space-time with a space-llike foliation by a one-parameter family $\Sigma_{t}$ and an open subset of it covered by a coordinate chart adapted to the foliation (e.g. Schwarzschild coordinates for the associated space-time) we can interpret the coordinate vector field $(\frac{\partial }{\partial t})^{a}$ as the "time direction" or "flow of time" (you can interpret $\nabla^{a}t$ in the same way since the vector fields will be proportional). This is of course a very specialized situation since general space-times don't admit such coordinate charts / foliations.

 

[WannabeNewton]

I don't get why people treat integral curves of $\nabla^{a}t$ so differently from integral curves of space-like vector fields, apart from the trivial differences. When space-like foliations exist, the hypersurface orthogonal vector field $\nabla^{a}t$ can geometrically be interpreted as the "flow of time". Anyone who has seen the Hamiltonian formalism of general relativity will not find anything alien in this as they will have seen even more general vector fields $t^{a}$ representing the "flow of time" chosen along with a time function $t$ such that the surfaces $\Sigma_{t}$ are space-like Cauchy surfaces and such that $t^{a}\nabla_{a}t = 1$.

 

[Whitefire]

Direction quite literally only pertains to spatial directions, not temporal ones.

I don't think we can resolve this without a really good definition of 'direction'. A one that we all would agree upon.

 

[Fredrik]

I don't think we can resolve this without a really good definition of 'direction'. A one that we all would agree upon.

There is a really good one that's agreed upon by everyone who understands it: A unit vector in the tangent space at the event where you want to assign time a direction.

Edit: A unit vector defines a direction in spacetime. But it can't by itself give us a reason to think of that direction as the direction of time.

The only thing that can define a direction of time is the kind of stuff that WannabeNewton is talking about. First you slice up spacetime into 3-dimensional hypersurfaces labeled by a real parameter t, so that each event belongs to exactly one of these hypersurfaces. Now if we want to find the direction of time at an event p, we would look at the hypersurface that p belongs to. There are two directions that are orthogonal to this hypersurface at p. In one of these directions, t is increasing, and in the other direction, t is decreasing. The direction that's orthogonal to the hypersurface and such that t is increasing, can then be considered the direction of time at p.

Note that this direction depends on our choice of how to do the "slicing".

 

[WannabeNewton]

Indeed so for the FLRW metric $ds^2 = -d\tau^{2} + a^{2}(\tau)dS^{2}$ just take $n^{a} = (\frac{\partial }{\partial \tau})^{a}$ which, in the coordinate basis, is just $n^{\mu} = \delta^{\mu}_\tau$ or put more suggestively $\mathbf{n} = (1,0,0,0)$. You can consider this as the time direction given the spatial slices $\Sigma_{\tau}$, which are of course orthogonal to $n^{a}$. Recall that $\tau$ is the proper time as measured by a clock carried along a chosen congruence of isotropic observers in the FLRW universe so the time direction is just pointing along the unit normal to this congruence i.e. $n^{a} = u^{a}$ where $u^{a}$ is the 4-velocity field of the congruence.

 

[Whitefire]

First you slice up spacetime into 3-dimensional hypersurfaces labeled by a real parameter t, so that each event belongs to exactly one of these hypersurfaces.

And why do you need to do the slicing? Why can't we consider a single point?

 

[Fredrik]

And why do you need to do the slicing? Why can't we consider a single point?

Because a point doesn't determine a direction. You need something like a point and a timelike curve through that point, or a point and a spacelike hypersurface through that point.

 

[Chalnoth]

And why do you need to do the slicing? Why can't we consider a single point?

Another way to look at it, in addition to Fredrik's point, is that time exists at every location, so while we're at it, why not define what we mean by time everywhere? Then we have a space-like surface which we can define as "now" everywhere, and the time direction points perpendicular to that surface (no, you can't visualize it, because it requires four-dimensional thinking to visualize, and we can only think in three dimensions).

Incidentally, one of the better discussions of extra dimensions is this one by Carl Sagan from Cosmos:

 

[write4u]

I don't think we can resolve this without a really good definition of 'direction'. A one that we all would agree upon.

Is "forward" sufficient? It does not rule out any precise direction except backward and sideways.

 

[Fredrik]

Is "forward" sufficient? It does not rule out any precise direction except backward and sideways.

"Forward" is the direction we're talking about how to define. Edit: I meant forward in time, not forward in space.

 

[write4u]

"Forward" is the direction we're talking about how to define.

Is the future a "direction"?

IMO, it is a valid question.

 

[Fredrik]

Is the future a "direction"?

In relativity, there are lots of directions that are labeled "timelike" (by a precise mathematical definition). Together they identify a region of spacetime that's sometimes called "the chronological future". The union of that set and its boundary is then called "the causal future". If what we mean by "the future" is one of these sets, then no, the future is not a direction. It's a set that identifies lots of different directions, not just one.

This is why we need something other than just an event in spacetime to single out which one of them to call the direction of time.

 

[write4u]

"Forward" is the direction we're talking about how to define. Edit: I meant forward in time, not forward in space.

Thank you for clarifying your definition. I agree.

 

[Chalnoth]

Yup. Forward in time is a direction. It's just not a direction you can point.

 

[write4u]

Yup. Forward in time is a direction. It's just not a direction you can point.

That was my initial response, there is only forward "in time".
But then the OP question becomes meaningless!

Can time be approached from a physical viewpoint at all. IMO to speak of direction is misleading. Along with different spacetime coordinates, time exist in latent form everywhere in the universe. I always thought of it as a non-causal universal potential.

In wiki, I saw the section of sets, but that is merely an exercise in probabilities. So the direction of time is a probability? A set of indicators which suggest the direction of time in the future?
This can be demonstrated by the double slit experiment, which shows a probability function of possible events, but what does that have to do with time itself or more to the point, direction?

OK, allow me to clarify this in my mind. If tomorrow is an (as yet) unspecified direction how can we make calculations for anything other than a generalized statement that time will be moving in an unspecified direction toward "somewhen", but always along with a series of chronological events, such as me traveling west on a train. The actual duration in time to complete my trip is affected by my physical speed, but not by my direction of travel.

It makes no sense to me. It is the worldline, the continuation of a series of events that creates a chronological time frame for that series of events. It stands to reason that there needs be change in the physical conditions (which require time) for time to become measurable by the duration of the event.

IMO, time ONLY comes into existence as result of a physical action which 'requires' and 'creates' time to be able to become instantiated in physical space at a specific coordinate, which undergoes change or is different than the starting coordinate. This bridging of physical events creates time in the process as a byproduct, a result.

Time does not exist by itself, it is a latency, a potential of spacetime, which becomes measurable only as a result of a change or action "in physical space". Whithout any physical change to measure, what is the need for time? Let alone direction.

The use of space by physical events creates a simultaneous "forward in time" chronology for those physical events, but only at the "time" of the event, no matter what direction the physical event itself follows. Time is a directionless latency, which allows reality to instantiate in chronological order, no more, no less..

Time is a result and cannot be measured at all without physical change. We can "assign" an estimate of the "time it will take" for an event to complete itself, but that is probabilistic and completely depends on the actuation of the event. But as soon as the event begins, time will record the actual time used going always forward in time along with the unfolding of the event.

How about a definition which states that time is a non-causal latency which becomes measurable only as a result of change and the duration of that event in spacetime. Therefore time can be measured (or even projected into the future) along with the direction of the event, but not independently by itself as a direction of time.

Fredrik,

The only thing that can define a direction of time is the kind of stuff that WannabeNewton is talking about. First you slice up spacetime into 3-dimensional hypersurfaces labeled by a real parameter t, so that each event belongs to exactly one of these hypersurfaces. Now if we want to find the direction of time at an event p, we would look at the hypersurface that p belongs to. There are two directions that are orthogonal to this hypersurface at p. In one of these directions, t is increasing, and in the other direction, t is decreasing. The direction that's orthogonal to the hypersurface and such that t is increasing, can then be considered the direction of time at p.

Note that this direction depends on our choice of how to do the "slicing".

This brings the question; can time be associated with a single point "p" at all? Then the conclusion the time in one direction "increases" and "decreases" in the other direction, sounds odd. If time does indeed increases or decreases in certain directions it is because space increases or decreases in size in those directions. IOW, the directions are spatial, not temporal.

Time follows no temporal direction other than the direction of spatial events, which may be in any direction. As the spatial events progress, time progress along with that worldline. But the counting of time is always forward, as it cannot do anything else, it is a non-causal result of a previous action.

Please consider any of my "assumptions" as probing questions. As a fan of Bohmian mechanics I am really interested in this discussion. Moreover, I do not seek to dispute any accepted theories, but try to stay within established knowledge.

 

[Fredrik]

In wiki, I saw the section of sets, but that is merely an exercise in probabilities. So the direction of time is a probability? A set of indicators which suggest the direction of time in the future?
This can be demonstrated by the double slit experiment, which shows a probability function of possible events, but what does that have to do with time itself or more to the point, direction?

I don't understand what you're talking about here, so I will just say that what we're talking about has nothing to do with quantum mechanics.

If tomorrow is an (as yet) unspecified direction how can we make calculations for anything...

Just pick a coordinate system and do the calculation in terms of the coordinates it assigns to events.

...other than a generalized statement that time will be moving in an unspecified direction toward "somewhen", but always along with a series of chronological events, such as me traveling west on a train. The actual duration in time to complete my trip is affected by my physical speed, but not by my direction of travel.

I don't understand anything you're saying here.

It is the worldline, the continuation of a series of events that creates a chronological time frame for that series of events. It stands to reason that there needs be change in the physical conditions (which require time) for time to become measurable by the duration of the event.

All time measurements (all clocks) involve some sort of change. That much is correct.

Along with different spacetime coordinates, time exist in latent form everywhere in the universe. I always thought of it as a non-causal universal potential.
...
IMO, time ONLY comes into existence as result of a physical action which 'requires' and 'creates' time to be able to become instantiated in physical space at a specific coordinate, which undergoes change or is different than the starting coordinate. This bridging of physical events creates time in the process as a byproduct, a result.

Time does not exist by itself, it is a latency, a potential of spacetime, which becomes measurable only as a result of a change or action "in physical space". Whithout any physical change to measure, what is the need for time? Let alone direction.

The use of space by physical events creates a simultaneous "forward in time" chronology for those physical events, but only at the "time" of the event, no matter what direction the physical event itself follows. Time is a directionless latency, which allows reality to instantiate in chronological order, no more, no less..

Time is a result and cannot be measured at all without physical change. We can "assign" an estimate of the "time it will take" for an event to complete itself, but that is probabilistic and completely depends on the actuation of the event. But as soon as the event begins, time will record the actual time used going always forward in time along with the unfolding of the event.

How about a definition which states that time is a non-causal latency which becomes measurable only as a result of change and the duration of that event in spacetime. Therefore time can be measured (or even projected into the future) along with the direction of the event, but not independently by itself as a direction of time.

This sort of stuff is much too speculative for this forum, so you need to stop including such things in your posts.

This brings the question; can time be associated with a single point "p" at all?

Yes, it can. But as I said in #47, you need something other than that point to identify a vector that we can think of as the direction of time.

Then the conclusion the time in one direction "increases" and "decreases" in the other direction, sounds odd. If time does indeed increases or decreases in certain directions it is because space increases or decreases in size in those directions. IOW, the directions are spatial, not temporal.

No, this is wrong. I'm talking about a line through point p that's orthogonal to the 3-dimensional spacelike hypersurface that we think of as "space". The parameter that labels the hypersurfaces will have some value t(p) at p. The point p divides the line into two pieces, one on which the parameter is greater than t(p) and one on which the parameter is less than t(p). The line has two tangent vectors of unit "length" at p. One of them points to the part of the line where the parameter has a greater value. It makes sense to think of that tangent vector as the direction of time.

 

[write4u]

Fredrik,

write4u,
This brings the question; can time be associated with a single point "p" at all?

Yes, it can. But as I said in #47, you need something other than that point to identify a vector that we can think of as the direction of time.

But what is the "something other"? Another set of points (a geometrical construct)?

This will be my last post on this subject, as I am not thoroughly familiar with tangents and vectors in spacetime other than as mathematical spatial geometric constructs.

But what I understand from what you just described seems to establish worldlines for a spatial reference system consisting of more than one point in space (by any other name). A "chosen" theoretical geometric reference system. IOW, in the experiment the experimenter can create any direction depending on the choice of coordinates (points). What the experimenter cannot do is alter the forward chronology of time intervals as it measures the spatial construct.

It is in the action of choosing vectors or tangents or any other geographic configuration that we create the apparent direction of time because time is always created during the action or the change and therefore would follow the spatial direction of the identified events or points.

IMO, the slicing experiment creates the condition of the direction of a worldline. Nevertheless, whatever spatial direction is indicated, it is a result of this action. If we were to change our reference points, the direction of time would follow those coordinates in space and the result might contradict the original directional tendency, but regardless of spatial direction time accompanies every event in every direction but always forward in time. Time itself has no direction except 'forward in time". There is no going 'backward in time' other than observationally and that's relativity, no? But even the act of observing the 'past' creates a worldline forward in time for the observer.

I do promise to look further into potentials of tangents and vectors, as right now they just seem spatial measurements, albeit in a sophisticated theoretical (geodesic) model.

Thank you for your patience and indulgence of my "speculations". I'll just observe to see if a consensus can be reached by the "learned fellows" about a direction of time which is other than forward in time.

Dang, one last question;

If I measure a square where the sides are 1 mile each. At 60 mph, I can establish a time measurement of 1 minute per side regardless of the direction of travel. When I arrive back at my starting point I will have traveled 4 minutes, the measurement chronology adding 1 minute for each side, but always accumulative and forward in time. If I have traveled 3 sides of the square and stop to measure the amount of time from where I came and measure the time it will take to the finish, I will notice that for this specific action more time lies in the "past" than is left in the "future" to complete the measurement. We can say 'we are almost there", but in this case where is 'there"? It is our starting point and we have spatially traveled 4 miles in the direction of 4 points (E,W,N,S.) of the compass but temporally we have traveled forward by 4 minutes in time, even as we ended up at the same starting point 4 minutes later.

I maintain that time is always a result coming into existence as a by-product of a physical event or physical change, or physical action in space, creating a worldline in spacetime. Of course space (a dynamic medium) itself is creating time and we have universal spacetime, but it is non-directional except that the dimension of time allows only the forward movement of time towards the future, along with the creation of future events.

Thanks for your patience.

 

[Spourk]

I maintain that time is always a result coming into existence as a by-product of a physical event or physical change, or physical action in space, creating a worldline in spacetime. Of course space (a dynamic medium) itself is creating time and we have universal spacetime, but it is non-directional except that the dimension of time allows only the forward movement of time towards the future, along with the creation of future events.

You kind of just answered all of your own questions.

 

[write4u]

You kind of just answered all of your own questions.

Thank you for the observation, but my question remains if am I wrong or not wrong but naive in my intuitions? As a layman my understanding of the universe comes from narratives. I trust that the scientific equations and formulas accompanying those narratives, are the proofs of those narratives.

Thus the question, does my narrative address the fundamental principle of the "time" part of spacetime as it pertains to the question asked in the OP?

 

[Fredrik]

But what is the "something other"? Another set of points (a geometrical construct)?

I answered that in #47, and yes, it's something geometrical.

But what I understand from what you just described seems to establish worldlines for a spatial reference system consisting of more than one point in space (by any other name). A "chosen" theoretical geometric reference system. IOW, in the experiment the experimenter can create any direction depending on the choice of coordinates (points). What the experimenter cannot do is alter the forward chronology of time intervals as it measures the spatial construct.

Sounds about right.

It is in the action of choosing vectors or tangents or any other geographic configuration that we create the apparent direction of time because time is always created during the action or the change and therefore would follow the spatial direction of the identified events or points.

Langauge like "time is created" isn't used anywhere in relativity, or in any other established theory of physics.

IMO, the slicing experiment creates the condition of the direction of a worldline. Nevertheless, whatever spatial direction is indicated, it is a result of this action. If we were to change our reference points, the direction of time would follow those coordinates in space and the result might contradict the original directional tendency, but regardless of spatial direction time accompanies every event in every direction but always forward in time. Time itself has no direction except 'forward in time". There is no going 'backward in time' other than observationally and that's relativity, no? But even the act of observing the 'past' creates a worldline forward in time for the observer.

I'm not sure I understand what you're saying, so it's hard to comment on whether this is right or wrong.

If I measure a square where the sides are 1 mile each. At 60 mph, I can establish a time measurement of 1 minute per side regardless of the direction of travel. When I arrive back at my starting point I will have traveled 4 minutes,

A clock at the corner where you start will tell you that 4 minutes have passed, but the number of minutes that you will have aged is
$$4\cdot\sqrt{1-\left(\frac{60\cdot\frac{1609.334}{3600}}{299792458}\right)^2}\approx 3.999999999999984.$$ This is if we ignore the that infinite acceleration is impossible in the real world.

the measurement chronology adding 1 minute for each side, but always accumulative and forward in time. If I have traveled 3 sides of the square and stop to measure the amount of time from where I came and measure the time it will take to the finish, I will notice that for this specific action more time lies in the "past" than is left in the "future" to complete the measurement. We can say 'we are almost there", but in this case where is 'there"? It is our starting point and we have spatially traveled 4 miles in the direction of 4 points (E,W,N,S.) of the compass but temporally we have traveled forward by 4 minutes in time, even as we ended up at the same starting point 4 minutes later.

In any inertial coordinate system, your spatial coordinates will be what they were at the start, but your time coordinate will be different. You are at the same location (in "space", as defined by the coordinate system), but at a different event (i.e. a different point in spacetime).

I maintain that time is always a result coming into existence as a by-product of a physical event or physical change, or physical action in space, creating a worldline in spacetime. Of course space (a dynamic medium) itself is creating time and we have universal spacetime, but it is non-directional except that the dimension of time allows only the forward movement of time towards the future, along with the creation of future events.

You're really giving me a hard time with comments like these. This is personal speculation and against the forum rules. There's no established theory of physics that says that time comes into existence as a byproduct of change, or that space creates time. The only reason I'm not giving you infraction points is that there are mathematical statements in SR that are somewhat similar to what you said.

1. An object moving in space traces out a curve in spacetime.

2. If there's a 1-parameter family of 3-dimensional spacelike hypersurfaces whose union is spacetime, then we can think of the parameter as time and the hypersurfaces as "space, at different times".

 

[write4u]

Thank you for your patience and your encouraging responses (except the last one

A clock at the corner where you start will tell you that 4 minutes have passed, but the number of minutes that you will have aged is (different)

Is this due to the direction or the speed of travel relative to the starting point?

1. An object moving in space traces out a curve in spacetime.

TY, this is basically what I was trying to express. I believe it is called a "world line", e.g. a chronology of its own existence within spacetime?

Earlier you asked me to clarify the term "set" of world lines which would afford a probability calculation. I believe those sets are called "world braids".

 

[Fredrik]

Is this due to the direction or the speed of travel relative to the starting point?

It's just the speed.

http://en.wikipedia.org/wiki/Time_dilation

 

[Whitefire]

Because a point doesn't determine a direction. You need something like a point and a timelike curve through that point, or a point and a spacelike hypersurface through that point.

Well, you will not get any argument from me here. Agreed 100%. However, can't you determine a direction from several points? You don't need to slice the Earth's surface into square yards to determine which way is up-- 3 points are enough. And if you substitute points for observers... why the slices?

@write4u: If there is any direction for time, 'future' is like 'forward' when driving a car. On the other hand, considering the fact that each point/observer moves into its 'future' with the 100% speed, I would say that 'future' (like 'forward') is a relative term and therefore a relative direction. When you compare many relative directions you can get a larger picture: that they are not necessarily the same; my relative 'future' and galaxy X relative 'future' are not the same futures/directions. Like with going 'west' by car. I can move 'west' by going south-west, west or north-west. I am always going 100% forward, but it is better to understand my north-west movement as what it is in relation to the larger frame of reference, not as 'less efficient movement west' (a.k.a: relative slower progress of time). In the case of time, we need the largest frame of reference possible--the entire universe, or at least what we see of it.

you can't visualize it

please ... a space-like *surface* ...

 

[WannabeNewton]

You are stuck thinking about vectors in the elementary sense from Euclidean space. First of all, we are trying to define a time-like basis vector at every point of space-time so obviously we need a vector field, we can't just take two points and subtract them to get a vector like in elementary physics. And if we want a notion of space at every instant of time then we need space-like hypersurfaces that fit together nicely under a continuous parameter - which we call "time". You can't visualize these hypersurfaces (the word surface here doesn't mean surface embedded in $\mathbb{R}^{3}$, which are the only kind of surfaces you can visualize).

 

[write4u]

Well, you will not get any argument from me here. Agreed 100%. However, can't you determine a direction from several points? You don't need to slice the Earth's surface into square yards to determine which way is up-- 3 points are enough. And if you substitute points for observers... why the slices?

@write4u: If there is any direction for time, 'future' is like 'forward' when driving a car. On the other hand, considering the fact that each point/observer moves into its 'future' with the 100% speed, I would say that 'future' (like 'forward') is a relative term and therefore a relative direction. When you compare many relative directions you can get a larger picture: that they are not necessarily the same; my relative 'future' and galaxy X relative 'future' are not the same futures/directions. Like with going 'west' by car. I can move 'west' by going south-west, west or north-west. I am always going 100% forward, but it is better to understand my north-west movement as what it is in relation to the larger frame of reference, not as 'less efficient movement west' (a.k.a: relative slower progress of time). In the case of time, we need the largest frame of reference possible--the entire universe, or at least what we see of it.

As I understand it, the time frame of the car where everything associated with the car all travel in the same direction at the same speed is called a 'world braid'. A set of world lines moving in the same coordinated direction through spacetime. Can we say that technically a person is a world braid, and if I was born @ 4:00 pm, May 24, 1953, my world braid as a person today spans 60 years, locally.

But what happens when the car breaks down and stops moving? The ensemble is no longer moving in any direction in space. Yet the car, parts, occupants all continue to go forward in time. But for the individual parts time has no specific direction other than forward and depending on the properties of the individual parts.

One might say that the world braid of coordinated movement of traveling in a certain direction has paused, but the ensemble itself of course continues on in spacetime, slowly decaying until the car is no longer a world braid but a random collection of individual world lines. A wheel falls off the car, I decide to start walking, I have a heart attack from the stress, etc.

Can a universal spacetime coordinated be established at all? Do we have a 'theoretical' map of every spacetime coordinate?
If east, west, north, south are 'local' directions, can a direction be identified within spacetime other than as another spacetime coordinate? How does one express; I am 'here at this time' but I am on my way "there when I get there", except by reference to local coordinates?

Aside from the accepted science of the properties of spacetime, when we are dealing with the creation of an individual world line or world braids (chronologies of individual events), I see the time part of an individual world line as a by-product created from the chronology of the various durations of these physical events (changes). I don't think this is in conflict with current spacetime science, is it?

 

[Whitefire]

You are stuck thinking about vectors in the elementary sense from Euclidean space

Yes, but it is mainly because I am convinced that 'now', even this 'now' we can't really see or experience because it is space-like, can be treated as euclidean space, and we can imagine and visualise it; in fact, we do it all the time. Given enough data, you could reconstruct such space-like hypersurface from, say, 8 minutes ago, all the way to the Sun, and as I understand, this reconstruction would be an euclidean space.

@write4u: I am sorry but I cannot just accept the idea that if you don't see the changes, this must mean that time doesn't flow. If you put a stone and a clock next to each other, do you really think that time doesn't flow for the stone, only because it doesn't show it? I do sometimes wonder whether absolute zero = time stop, but it seems like mixing symptoms with the cause of the sickness.

 

[Fredrik]

Yes, but it is mainly because I am convinced that 'now', even this 'now' we can't really see or experience because it is space-like, can be treated as euclidean space, and we can imagine and visualise it; in fact, we do it all the time. Given enough data, you could reconstruct such space-like hypersurface from, say, 8 minutes ago, all the way to the Sun, and as I understand, this reconstruction would be an euclidean space.

This works when we're dealing with inertial coordinate systems in SR, but it doesn't work in GR, or even when we're dealing with non-inertial coordinate systems in SR.

 

[write4u]

Yes, but it is mainly because I am convinced that 'now', even this 'now' we can't really see or experience because it is space-like, can be treated as euclidean space, and we can imagine and visualise it; in fact, we do it all the time. Given enough data, you could reconstruct such space-like hypersurface from, say, 8 minutes ago, all the way to the Sun, and as I understand, this reconstruction would be an euclidean space.

@write4u: I am sorry but I cannot just accept the idea that if you don't see the changes, this must mean that time doesn't flow. If you put a stone and a clock next to each other, do you really think that time doesn't flow for the stone, only because it doesn't show it? I do sometimes wonder whether absolute zero = time stop, but it seems like mixing symptoms with the cause of the sickness.

I may not have expressed it with clarity. I agree with your example of the stone. And of course, if we wait long enough we can indeed see the stone 'age' (I used the 'wheel falling off' the car').

 

[Ogr8bearded1]

As one layman to another, perhaps it is the view that is off and causing problems. Maybe time is outside of what you are trying to say. I'll give an example. I'm in a car traveling North so my direction to all I can see is North. However the Earth is rotating, so to an observer not on Earth it would appear I'm traveling very slowly North and quickly East IF he were mapping your progress as a space point. Think of East as the forward of time, regardless of your true direction you head East. Even if the movement is OUTSIDE of your ability to observe. So I went North and time went forward. If I turn around and head South, I'm still really moving East and time is going forward. Even if I go East, my view of how fast I'm going East is still slower than my actual movement East and I'm still going forward in time. So yes, time has a direction, but it is one outside of perception. You notice its effects (the Sun moves higher in the sky) but not its affects on your direction of physical travel.

Also, I think its important to not confuse time with the measurement of time. Some say time is movement and without movement there is no time. To me, they are talking about the measurement of time (and that rock, its atoms are moving even if it is still.) Smolin says time may be fundamental. If you haven't read the post and seen the talks I'd say you should give it a look here. https://www.physicsforums.com/showthread.php?t=683198

One of the best thoughts on time I have heard was when someone stated "Do we stand still and time moves, or do we move and time stands still?" If we can't really answer this question then figuring out 'why' it always, to our perception, moves forward may be impossible.

 

[write4u]

@write4u: I am sorry but I cannot just accept the idea that if you don't see the changes, this must mean that time doesn't flow. If you put a stone and a clock next to each other, do you really think that time doesn't flow for the stone, only because it doesn't show it? I do sometimes wonder whether absolute zero = time stop, but it seems like mixing symptoms with the cause of the sickness.

After a little more reading I discovered I was talking about a 'world knot', where a world line ceases.