Preferred direction

[chriscurtis]

If it is common understanding that there is no preferred direction in the observable Universe and time is one of four observed dimensions, why does time seem to have only one observable direction? This is a stupid question right?

[G O R T]

I can look in both directions of time. As in other dimensions, if you do not have the means to overcome your inertia, you keep going.

Course' this brings up the whole destiny/free will thing.

[Kaptain K]

...why does time seem to have only one observable direction?

We don't know!

This is a stupid question right?

No.

Course' this brings up the whole destiny/free will thing.

Freewill is a golden thread woven through the matrix of fixed events!

[a1call]

...why does time seem to have only one observable direction?

We don't know!

I would like to respectfully object to the use of the plural pronoun.

I question that being the mainstream view.

[hhEb09'1]

I would like to respectfully object to the use of the plural pronoun.

I question that being the mainstream view.

Go ahead and explain what the mainstream view is.

[a1call]

Correct me if I'm wrong, but
* Isn't time travel more the realm science fiction rather than serious science?
* Hasn't this been discussed to death on this board?
* Has there been any confirmed mainstream possibility of "Back to the future"?

[hhEb09'1]

Correct me if I'm wrong, but
* Isn't time travel more the realm science fiction rather than serious science?

Certainly!

* Hasn't this been discussed to death on this board?

Like everything else.

* Has there been any confirmed mainstream possibility of "Back to the future"?

Not to my knowledge

But how does all that make Kaptain K's comments ATM?

[a1call]

But how does all that make Kaptain K's comments ATM?

I never mentioned ATM.
I apologize for any such implication.

I think the answer to why, is as simple as because it's according to the definition of what time is. No big mystery here.

[hhEb09'1]

I question that being the mainstream view.

I never mentioned ATM.

??

I think the answer to why, is as simple as because it's according to the definition of what time is. No big mystery here.

What's the "definition" of time? and how does it say that time has to have only one direction?

[John Mendenhall]

??
What's the "definition" of time? and how does it say that time has to have only one direction?

Try here:

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

[hhEb09'1]

Try here:

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

No, I don't think so--the closest thing there is the discussion about the arrow of time. Most of the first part of that discussion at the head of the article just seems to make Kaptain K's point.

[John Mendenhall]

If it is common understanding that there is no preferred direction in the observable Universe and time is one of four observed dimensions, why does time seem to have only one observable direction? This is a stupid question right?

No preferred reference frame is a better way to put it. And now that I think about it, for any real reference frame defined x=0, y=0, z=0, and t=0, t starts incrementing immediately.

[hhEb09'1]

No preferred reference frame is a better way to put it. And now that I think about it, for any real reference frame defined x=0, y=0, z=0, and t=0, t starts incrementing immediately.

So do x, y, and z

[astromark]

If it is common understanding that there is no preferred direction in the observable Universe and time is one of four observed dimensions, why does time seem to have only one observable direction? This is a stupid question right?

The laws of physics decrees that time moves at its relentless pace and direction since the Big Bang and until now. We have not the knowledge to stop it or even move through it. It comes at us at the speed of light and is history in an instant. We get older. Good question, with no answer. Its just the way it is. Its not the question that is stupid. The answer is difficult to clarify.

[John Mendenhall]

So do x, y, and z

Yes, I know. But I don't think it's as inexorable and predictable as t. And also, you have to decide from where to measure.

The more we know, the less we know we know.

[Ken G]

You often hear that "time is just like another spatial dimension", but that isn't true. There are at least two ways that time is fundamentally different from distance. One has to do with the sign that appears in the relativistic metric, which basically means that distance acts like an imaginary (in the sense of the square root of minus one) version of time. That sign difference organizes spacetime in a way that some events can unambiguously be said to occur after other events, which is important for the second big difference-- time organizes the configurations of very large systems such that more likely indistinguishable configurations spontaneously follow less likely ones, never the other way around. How that involves our own minds, in saying what is meant by "indistinguishable", is pretty subtle, but certainly within the contexts of how our minds work, there is a clear arrow to macroscopic time, but not to macroscopic space.

[chriscurtis]

It's interesting. The reason I asked was that I remember physics theories are good if they make predictions that may be observed. Since we cannot observe the movement of time backwards, how can we test that the laws of physics are the same when you reverse CPT? Its like speculating about what's outside our past and future light cones isn't it?

[Svemir]

I remember an ATM page where the author said (I don't know if it's still active) that the existence of the 4th spacial dimension (orthogonal to x, y and z) will be perceived by us as Time. In that sense the answer to the question " Why is there only one direction of time?" is simple, as there is no negative distance.
In some reference frame (strong gravity, as in Black Holes) there is no distinction between time and space dimensions (right?).
In our mind (inclined to make apstractions) the time is separated from the space but in reality you don't have time or space alone.
You have an event (Einstein) which in the case of one-dimensional space could be expressed with ds/dt.
In the case of our 3-dimensional space, I don't know, maybe Schrödingers equation.
So, when you say time , it's no more then an apstraction, which we measure the change with. It's no more real then Santa Claus.

[hhEb09'1]

Since we cannot observe the movement of time backwards, how can we test that the laws of physics are the same when you reverse CPT? Its like speculating about what's outside our past and future light cones isn't it?

That's not what is meant, though. The physics laws we have are the same. We don't know if they are good.

[Ken G]

That's not really what CPT symmetry means-- we don't reverse time, it's true, but we also can't reverse P or C (we can't reflect our universe through itself, we can't make an antiparticle be a particle). What it does mean is that if we make replacements to the initial conditions that correspond to a CPT inversion, do we see the same physics unfold? The P means we swap the places of the particles, the C means we replace particles for antiparticles, and the T means we reverse all the velocities (and anything else with an odd power of t in its units, but that's pretty much velocity).

[chriscurtis]

Are these things be related in any way:
the excess of matter over antimatter and the arrow of time?

[Ken G]

I don't know if there's any direct connection, but maybe there's an argument that it is "more likely" that there should be some matter/antimatter discrepancy than a perfect balance, so time going forward would tend to find that more likely state.

[hhEb09'1]

I don't know if there's any direct connection, but maybe there's an argument that it is "more likely" that there should be some matter/antimatter discrepancy than a perfect balance, so time going forward would tend to find that more likely state.

Like the drunkard's walk? Where the most likely point is the origin, but the most likely distance from the origin is not zero?

[Ken G]

Yes, very much like that. So the next time you see a drunk stumbling around, he might actually be in some small sense re-enacting the process of creation of our universe-- give him a ride home.

[Warren Platts]

You often hear that "time is just like another spatial dimension", but that isn't true. There are at least two ways that time is fundamentally different from distance. One has to do with the sign that appears in the relativistic metric, which basically means that distance acts like an imaginary (in the sense of the square root of minus one) version of time. That sign difference organizes spacetime in a way that some events can unambiguously be said to occur after other events, which is important for the second big difference-- time organizes the configurations of very large systems such that more likely indistinguishable configurations spontaneously follow less likely ones, never the other way around. How that involves our own minds, in saying what is meant by "indistinguishable", is pretty subtle, but certainly within the contexts of how our minds work, there is a clear arrow to macroscopic time, but not to macroscopic space.

Another arrow through time is natural selection. The less-well adapted always precedes the better adapted.

But the big, real difference between space and time is phenomenological. Time and space are just experienced differently. This was Whitehead's argument against relativity. Just look at it! Well, you can look at things in space, but you can't see things in time--except for NOW!.

[Boxes]

I hesitate to mention this, but couldn't you say that in the reference frame of most points in the universe we will only ever be able to travel away? That is, to them we are red shifted to an extent that no current, and possibly no future propulsion system could overcome the speed at which we are traveling away.

So don't we already have an arrow of space as well as an arrow of time wrt/most points in the universe?

[Ken G]

Time and space are just experienced differently. This was Whitehead's argument against relativity. Just look at it! Well, you can look at things in space, but you can't see things in time--except for NOW!.

But Whitehead's argument has nothing to do with relativity, because relativity does not say space and time are the same. In fact, it says how they are different.