Why is there a "now"?

[Zeph]

Originally Posted by Michael C
If there were conscious beings in such a region, how would they experience time? Since all processes are reversed, peoples brains would be going backwards: they'd "remember" things that will happen in the future. Would the experience of time for a conscious being in a time-reversed region in fact be any different from our experience? I can't see how.

I'm not sure if there would be any particular differences in how they experience time, again since as you note “all processes are reversed, peoples brains would be going backwards:” and they would remember what we would consider to be the future just as we remember what they would consider to be the future.

Hmm. Here we perhaps switch roles. I don't see the question of time flowing in an opposite direction in such a region as meaningful unless there is some interaction between our region and that one. Suppose that beyond the singularity of a black hole there is another 4space universe similar to ours but completely unable to convey information to or from ours. However, time flows backward there compared to our time. But - absent some *common* frame of reference by which to measure "backward" and "forward", absent any way for information to cross between, how would that be meaningful?

On the other hand, if some region in our universe with which we can interact and transfer information has time flowing "backward" and entropy decreasing (as we see it), just how would that make sense? Can high entropy particles (or information) from the future of our universe enter that region during its low entropy "past" and have their worldlines carried (forward in that universe, backward in ours) to that region's future (our past) only to eventually reenter our universe in our past?

There would be at least one physical difference that I can think of though, however irrelevant it is actually. For example Sol mentioned charge reversal in CPT symmetry. So although what we call a positive charge would become what we would call a negative charge, like charges would still be alike and different charges would still be different. Just as we remember unlike charges separated in the past coming together in the future and like charges together in the past becoming separated in the future their experience would be the opposite. Unlike charges together in their past would separate in their future and like charges separate in their past would come together in their future. The keys points being that we would both see unlike charges still as unlike, like charges would still be the same as each other and there would still be a difference in the behavior of like charges from that of unlike charges. The only difference being that we would claim unlike charges attract (come together in our future) and like charges repel (move apart in our future), while they would claim like charges attract (come together in their future) while unlike charges repel (move apart in their future).

Sol, is this your understanding of CPT reversal? That like charges would attract? I don't believe that anything very "like" our universe would exist in that case. I have no problem accepting that in a flipped universe, vacuum tubes could have the same dynamics as ours do, but using what we call positrons rather than electrons. But I believe that the nature of atoms and molecules would be entirely different than they are in our universe if like charges attracted. Simplistically, a positive charge can easily occupy a time reversed orbit around a negative charge, which is entirely similar to the reverse situation in time and charge, so long as positive and negative still attract. If they repel, there is no orbit, and all the anti-protons in the universe clump together through gravity and charge as well as the nuclear forces. Such a universe is fundamentally different, not simply a time reversal of our own.

 

[The Man]

Hey, the man, relax a little.

What makes you think I'm not already relaxed quite a substantial amount?

I'm not frustrated, I said I was feeling friendly, not hostile or scornful.

"feeling friendly, not hostile or scornful" don't exclude being frustrated.

OK, so you're not frustrated, have you found the answer you were looking for yet?

My amusement is with the human condition, which we all share, myself included. I was also hypothesizing from the tone I perceive that some others might be slipping into (perhaps unnecessary) frustration, but I wasn't 'laughing in frustration' as you misread me.

Nope, I was simply pointing out that the frustration you perceive may simply be yours at not finding what you seek by looking in the wrong place.

You really haven't been reading very carefully; I don't mean that so much as a put-down, as to describe that if you tried a bit harder to understand in a friendly manner, you might not need to be so reactive to things I didn't actually say upon closer reading. Unless you prefer sniping at phantoms more than engaging with other thoughtful (even if horribly incorrect viewpoints, I invite a bit closer reading before reacting.

Actually I have been reading quite carefully and trying to point you in the direction of the type of answers you're apparently seeking. Again if you don't find the scientific and mathematical answers satisfying then I once again invite you to look somewhere other than a science and math subsection of this forum.

Likewise, it seems that you really missed what I found ironic. There's no inconsistency there. Let's try it point by point:

I asserted (for discussion purposes) in effect that science seems able to explain only as much of the subjective phenomenon of "now" as DOES fits into an analogy with "here" and that any further characteristics of the concept of "now" which DO NOT fit into that analogy are weakly handled if at all. (Paraphrasing).

Some others responded to the effect that (in their scientific framing) "now" was just like "here", and discounted (from their scientific framing) that there was any scientifically meaningful characteristics of "now" beyond those which analogize with "here".

This was agreeing with my hypothesis, not disagreeing, yet they appear not to have read closely enough to realize that.

Pay careful attention to the adjective "scientific" and the adverb "scientifically" in my quoted and unquoted sentences. Those were carefully used as important qualifiers, the omission of which could have indeed made my sentence seem to contradict earlier assertions. I have agreed from the start that "scientifically" there is little distinction between "now" and "here" (at least in terms of our current understanding, unless there's something new I haven't yet encountered but can hope for).

So let's just be totally clear that the conception of "now" which is well handled in science is indeed very analogous to the concept of "here". It's just an arbitrary point in 4 space, made special if at all by some observer whose worldline passes through there and who thereby gives it undue weight. Everybody here gets that, and I've seen no serious disagreement. Really. And certainly not from me! That's exactly what I learned in science.

However, the concept of "now" as a moving point where the undetermined future becomes the determined past, is a primary experience of almost all highly conscious beings to the best that we can tell. It might be explained as an illusion someday, but it doesn't go away just because we don't have a mathematical or physical model of it yet. THAT concept of "now" is NOT closely analogous to "here" and is thus outside the realm and tools of science, so far. It's hard to even translate this concept into scientifically meaningful terms, so it appears to be "nonsense" with regard to the scientific method, again so far.

And yes, that broader (or more subjective) concept of "now" does have several fundamental differences from "here", which the more limited "scientific" concept of "now" does not.

So again you're not looking for a ""scientific" concept of "now"", which is probably why your search will continue to be frustrated on a scientific subsection of this forum.

Yet I find some of the quantum mechanical edges of science do seem to be grappling with phenomena not formerly within the realms of traditional science, and I find it worth asking from time to time whether theorists have made any progress in scientifically addressing the broader concept of now, past and future. That's why I ask here.

Fine then discuss those "quantum mechanical edges of science". In scientific and not philosophical terms (you'll please note the qualifiers).

"No, that's still outside the tools of science, check with the philosophy department" is one perfectly reasonable answer. No scorn or frustration needed. No harm, no foul, for asking.

Quantum mechanics is a tool of science, and a very effective one at that. Perhaps the most effective tools of science that we have in our "tool box".

On the other hand, Sol Invictus and others have suggested that the subjective "now" could be illusion. I too find that credible and would welcome a scientific description of the mechanisms behind such an illusion, as we have for many other subjective or local framework illusions. I easily concede that might a a fruitful approach; I just don't see that it has yet borne scientific fruit.

Again as I said before look to physiology and perhaps some psychology for that particular "scientific fruit".

Two further rough suggestions of mechanism have arisen here (and elsewhere). One is that in effect C is a pretty big number; in physical space we tend to interact mostly with things around the light-nanosecond to light-microsecond scale, but time in the seconds to hours scales, which are disparate. That is, the scales of the time axis and the spatial axes are very different in the "everyday life" that imbues our consciousness, and this disparity of scale explains the subjective illusion of "now". While intriguing, upon examination I do not find that sufficient "mechanism" to explain the putative illusion, tho further discussion would be welcome.

Again it is not just the scale of C it is the time scale of our own ability to perceive that makes one believe what they perceive is in fact "now" as opposed to just the past.

The other is that entropy increase at near infinite rates, such that our consciousness cannot project certainty even a femtosecond forward, but the correspondingly lower entropy of the past allows us to have a fixed and immutable past extending billions of years. I'm still weighing this one. I haven't so far encountered any mathematics supporting the concept that entropy is increasing at such near infinite rates, so I'm not sure but that this proposed explanation is more than hand waving. I also don't see any full picture of how this ties to the subjective experience of now as the junction of future and past, but I'm still considering it and plan to do more reading.

"entropy is increasing at such near infinite rates"? Guess that heat death of the universe is only a "femtosecond" away now?

Your consciousness is a conglomeration of neural impulses that occur over some period of time and space in your brain. Which puts it in the past as well as perhaps the future, at least in the sense of a mathematical point as "now" with no temporal extents. As well as putting it "there", over "there" and some a bit more over "there", with a mathematical point as "here" having no spatial extents.

I have always been a "curious character", temperamentally not unlike Feynman even if far less brilliant intellectually. I seek out others of like temperament. My hypothesis is that some of them will gravitate towards non-dogmatic skepticism. I'm coming to another hypothesis which is that they might tend to avoid online skeptical forae for some strange reason. (wry but not hostile grin).

"dogmatic skepticism"? Talk about irony and inconstancy (indeterminate facial expression).

 

[Emperor_Gestahl]

I agree completely.


http://www.internationalskeptics.com/forums/showthread.php?postid=6698185#post6698185

Haha sorry I didn't read the thread, though at least my apology continues the important work of linking this at people.

 

[The Man]

Haha sorry I didn't read the thread, though at least my apology continues the important work of linking this at people.

Perhaps the most important work on this thread. No need to apologize for doing the important work.

 

[sol invictus]

Context 1. Yes, I take that as the step one. In that way, "now" is quite similar to "here", I think we all agree. It is indeed a very powerful and useful way of understanding the world.

Context 2. Here's the followup distinction which I haven't heard much acknowledged, and which I'll frame to this analogy. The arctic circle may or may not be north of both of us. Jan 12, 2012 2am PST is however in the future for both of us. (And for some very long period will be someday be in the past for both of us; the transition may vary by some microseconds). Of course, that's "merely" because we happen by some strange coincidence to always share an approximate t position which is pretty close to each other, even while our latitudes are completely independently chosen.

You keep trying to explain your position by assuming it. I don't agree that we share a common now - so comments like the bolded one are nonsensical for me.

There is no sense in which our latitudes change together in any way, even roughly. There is a strong sense in which our t locations change together (albeit never exactly so for reasons well accepted by all). There is no sense in which my latitude + 1 arc-second can be guaranteed to be greatly different in quality than my latitude - 1 arc-second, but the situation with my t location +/- even a small delta are extremely different in fundamental ways, being future and past. In these ways, "now" is not very similar to "here".

You have that backwards, really - it's our temporal positions that can differ by the most. Let me try to explain that in a way I mentioned once before, but maybe didn't register.

Think of spacetime as a 2-dimensional surface, like a piece of paper. Time is up, space is across. An object at rest is represented by a thick vertical line. An object in motion is a wavy line (these are called "worldlines"). A horizontal line would be something that exists everywhere for one moment - it's an instant, if you like. No line representing a physical object or person is ever at 45 degrees or more from the vertical, because we are using units where light travels at 45 degrees (i.e. the vertical axis is ct). OK?

Now imagine our two worldlines drawn on this diagram. We can either use a frame in which the earth is always at rest, or not - that's up to us. If it's it rest, our two world lines are nearly vertical lines, very close together (on the whole sheet, which is the size of the universe), with tiny little wiggles as we move around on earth. One line begins before the other (whichever of us is older), and one line ends first.

This post originated as a little dot somewhere on my worldline, after which it was transmitted along a line to you (and along other lines ro others) that read it later. If you reply, that's a line originating on your world line and going back to mine, etc.

Nowhere in this picture is there any need or room for a common "now". As I hope you can see, your assertion above that our heres aren't correlated is not true, and might seem true only in one extremely special frame (earth at rest) - and on the other hand even in that frame most randomly chosen points on our respective worldlines differ by many years in time. In a frame where the earth is moving at or near the speed of light our worldlines will both be nearly at 45 degrees (and very tightly correlated). In a frame where the center of the milky way is at res our worldlines are a pair of nearly coincident stretched helices, with tiny independent additional wiggles.

 

[Perpetual Student]

Nowhere in this picture is there any need or room for a common "now". As I hope you can see, your assertion above that our heres aren't correlated is not true, and might seem true only in one extremely special frame (earth at rest) - and on the other hand even in that frame most randomly chosen points on our respective worldlines differ by many years in time. In a frame where the earth is moving at or near the speed of light our worldlines will both be nearly at 45 degrees (and very tightly correlated). In a frame where the center of the milky way is at res our worldlines are a pair of nearly coincident stretched helices, with tiny independent additional wiggles.

Looking at two vertical and (approximately) parallel world-lines, when we draw a horizontal line through them, do not the two world-lines share a common t at the two points of intersection?

 

[Michael C]

Two further rough suggestions of mechanism have arisen here (and elsewhere). One is that in effect C is a pretty big number; in physical space we tend to interact mostly with things around the light-nanosecond to light-microsecond scale, but time in the seconds to hours scales, which are disparate. That is, the scales of the time axis and the spatial axes are very different in the "everyday life" that imbues our consciousness, and this disparity of scale explains the subjective illusion of "now". While intriguing, upon examination I do not find that sufficient "mechanism" to explain the putative illusion, tho further discussion would be welcome.

C is big to us. Whether we consider something to be "big" or "small", or a time to be "long" or "short" depends on our own dimensions in time and space. Consider some conscious beings who were accustomed to moving relative to one another at speeds near that of light: they wouldn't see C as a huge number. For them, the relativity of simultaneity and of distance would be normal, commonplace experiences. For them, "now" would be relative, much like "here". These beings wouldn't consider that they shared the same "now" more than the same "here".

Context 2. Here's the followup distinction which I haven't heard much acknowledged, and which I'll frame to this analogy. The arctic circle may or may not be north of both of us. Jan 12, 2012 2am PST is however in the future for both of us. (And for some very long period will be someday be in the past for both of us; the transition may vary by some microseconds). Of course, that's "merely" because we happen by some strange coincidence to always share an approximate t position which is pretty close to each other, even while our latitudes are completely independently chosen. There is no sense in which our latitudes change together in any way, even roughly. There is a strong sense in which our t locations change together (albeit never exactly so for reasons well accepted by all). There is no sense in which my latitude + 1 arc-second can be guaranteed to be greatly different in quality than my latitude - 1 arc-second, but the situation with my t location +/- even a small delta are extremely different in fundamental ways, being future and past. In these ways, "now" is not very similar to "here".

Here again you are using subjective words like "greatly", "roughly". If we say that a second is a "short" period of time, then we could logically say that a light-second is "short" distance. In terms of light-seconds, we are all very close together. You say:

"we happen by some strange coincidence to always share an approximate t position which is pretty close to each other, even while our latitudes are completely independently chosen."

If we measure everything in seconds, we are as far away in time as we are in space. You say that our latitudes are "completely independently chosen" but in fact we're all stuck on the same Earth, so we know that we can't be more than a certain distance apart. If we consider that our t positions are "pretty close", we may logically say that we also are "pretty close" in space. That's probably how the beings I describe above would see it.

 

[sol invictus]

Looking at two vertical and (approximately) parallel world-lines, when we draw a horizontal line through them, do not the two world-lines share a common t at the two points of intersection?

Of course. But why should the line be horizontal? Why should we draw it at all? Why should we only consider two points at a time?

 

[Perpetual Student]

Of course. But why should the line be horizontal? Why should we draw it at all? Why should we only consider two points at a time?

We are discussing the concept of "now." So, let's begin by agreeing on the concept of a shared point in time, and see if we can pin down "now" as a special point in time.
So, using your two dimensional model of space-time, you are sitting in your living room in Nova Roma, Kentucky and here I am seated in La Quinta, California. Those squiggly vertical lines that describe our world lines are some distance apart and, while we are seated, keep the same distance along the vertical axis, disregarding some very tiny movements due to our arms gesturing, breathing, etc. and some minuscule seismic movements between us. So, since we are in the same inertial frame we share the same t. Is that not so? If v is zero in [latex] t* = (t-\dfrac{vx}{c^2})}/{\sqrt{1-\frac{v^2}{c^2}}[/latex], then t* = t.
So, in your simplified two dimensional depiction of spacetime, any straight horizontal line represents a shared point in time for all objects in the same inertial frame (all points on that line). The points on any straight line not horizontal represents simultaneity for objects in relative motion that touch that line.
So, if I contemplate the current moment (now) it is also the current moment (now) for you. Any problems with that?

 

[sol invictus]

We are discussing the concept of "now." So, let's begin by agreeing on the concept of a shared point in time, and see if we can pin down "now" as a special point in time.
So, using your two dimensional model of space-time, you are sitting in your living room in Nova Roma, Kentucky and here I am seated in La Quinta, California. Those squiggly vertical lines that describe our world lines are some distance apart and, while we are seated, keep the same distance along the vertical axis

Horizontal. Vertical is time.

disregarding some very tiny movements due to our arms gesturing, breathing, etc. and some minuscule seismic movements between us. So, since we are in the same inertial frame we share the same t. Is that not so?

No, it is not - in fact it makes no sense at all. We are not "in" a frame, or rather we are in all frames. Frames are coordinate systems - the same spacetime populated with people and objects can be described in an infinity of possible frames, and everything in the spacetime is in every one of them. In my 2D spacetime, frames are just labelings of points. If you pick two spacelike separated points on our worldlines you can find a frame in which they are at the same time, and an infinity of others in which they aren't.

So, in your simplified two dimensional depiction of spacetime, any straight horizontal line represents a shared point in time for all objects in the same inertial frame (all points on that line). The points on any straight line not horizontal represents simultaneity for objects in relative motion that touch that line.
So, if I contemplate the current moment (now) it is also the current moment (now) for you. Any problems with that?

Yes. See above.

Look - let's draw a vertical line that passes through your living room in La Quinta at a time you were there. We know that line passes through your worldline at least once. Suppose it also passes through mine (meaning at some point in the past or future I occupied the same spatial location your living room did at a time when you were there). Does that mean we can think of that vertical line as our shared "here", and therefore conclude that we share a common "here"?

I don't know how to make sense of such a statement, but (in 2D at least) it's completely equivalent to the one you're arguing for.

 

[Perpetual Student]

OK, I am indeed confused! Is it not true that if our watches are exactly synchronized and there is no relative motion between us, we (you in Nova Roma and me in La Quinta) will exactly agree on the time of some event we both see (after we take into account the speed of light)?

 

[sol invictus]

Sure. Of course we can agree on the coordinates of a spacetime event - both its time and its location.

 

[Perpetual Student]

Sure. Of course we can agree on the coordinates of a spacetime event - both its time and its location.

OK, then it follows that we can also agree that our t coordinates are identical for some period of time.

 

[sol invictus]

OK, then it follows that we can also agree that our t coordinates are identical for some period of time.

If we choose a coordinate system, then obviously for some points on your worldline, there will be a point on my worldline with the same time coordinate. But in a different coordinate system, the same points on our worldline will correspond to different points on mine.

The point is that our lives aren't a succession of uniquely shared nows - they are two different lines in 4D. There isn't a unique way to choose a time slicing. You can simply make a choice, and that's fine, but it's of no physical significance.

Just think of drawing two lines on a piece of paper. Obviously you can put a grid down, and then identify points on the lines that fall on the same grid line. But the reality is the two lines, not the grid - and a different grid will give a different identification.

 

[Perpetual Student]

I guess my understanding of this is not what I thought it was. If we are at relative rest, I had thought all coordinate systems would assign the same t for us because if we have the same v relative to some other inertial frame, we both have the same t* (in accordance with the equation above, post #169). What's wrong with that thinking?

 

[Perpetual Student]

Wait a minute! Are we back to talking about coordinate systems like one would have while standing on a "stationary" Phobos? Could we limit this discussion to inertial frames of reference?

 

[Vorpal]

Since your proper time is the length of your wordline, it's natural to interpret it as your time axis and whatever's instantaneously orthogonal to it as your "now". In SR, there is a unique well-defined way to transport vectors over all of spacetime consistently, so you can extend them into a hyperplane. This gets you exactly what is conventionally meant by "now" in SR, with simultaneity defined by Einstein synchronization^WP. It's the coordinates defined in this particular manner for inertial observers that follow the transformation you have in post #169.

That's the interpretation that I've been operating under previously, but Sol's completely right in that nothing breaks if we don't follow that convention. It's not necessary. And in GR, it's not only unnecessary, but usually impossible to follow in the first place.

 

[sol invictus]

I guess my understanding of this is not what I thought it was. If we are at relative rest, I had thought all coordinate systems would assign the same t for us because if we have the same v relative to some other inertial frame, we both have the same t* (in accordance with the equation above, post #169). What's wrong with that thinking?

If we are at rest in some inertial coordinate system, then in that coordinate system there is an identification (equal coordinate time) between points on my worldline and points on yours. If we are not at rest in some inertial coordinate system, in that coordinate system there is still an identification (equal coordinate time) between points on my worldline and points on yours. If we use a non-inertial coordinate system in which you are moving in figure 8s and I'm spinning like a top, there is still an identification (equal coordinate time) between points on my worldline and points on yours.

In any coordinate system there is such an identification, because that's what coordinate systems are. But that statement contains almost now physics content, and it quite obviously does not mean we have a shared now - since most such identifications will be different.

Incidentally - if you are in California and I'm in Kentucky, we are definitely not both at rest in any inertial coordinate system - don't forget that the earth is rotating at 1000mph at its surface. And even ignoring the rotation, gravity means that there are no inertial coordinate systems at all, full stop. However whether or not one exists and whether or not we are at relative rest in it is irrelevant to the question asked in this thread. Two parallel straight lines do not "share a common x" any more than two non-parallel wiggly lines.

That's the interpretation that I've been operating under previously, but Sol's completely right in that nothing breaks if we don't follow that convention. It's not necessary. And in GR, it's not only unnecessary, but usually impossible to follow in the first place.

Exactly - it's not necessary, and it's a convention. It's no more indicative of reality than the fact that the english word for apple is spelled a-p-p-l-e.

 

[Perpetual Student]

Thanks. Are there any other counter-intuitive concepts of modern physics that you would like to toss my way? Just when I think I'm making some progress with this stuff, my brain is smothered in another layer of incomprehensible convolutions. Actually, I think I am getting somewhere here -- slowly!

 

[Vorpal]

You may want to follow up on Einstein's hole argument^WP for general covariance (which, ironically, was originally an argument against general covariance). And also this:

The method hitherto employed for laying co-ordinates into the space-time continuum in a definite manner thus breaks down...
All our space-time verifications invariably amount to a determination of space-time coincidences. If, for example, events consisted merely in the motion of material points, then ultimately nothing would be observable but the meeting of two or more of these points. Moreover, the results of our measurings are nothing but verifications of such meetings of the material points, coincidences between the hands of a clock and points on the clock dial, and observed point-events happening at the same place at the same time.

Or, in more modern language, "coincidence" = "intersection" and "motion of material points" = "worldlines". Any particular correspondence between points on distant worldlines, such as "sharing the same now", is not measurable and fairly arbitrary.