Why is there a "now"?

[Perpetual Student]

I can understand time as a ratio of motion. We use time to describe how much some object has moved relative to how much some other object has moved.

Define "moved" without reference to time.

 

[NoCoPilot]

Actually the concept of "now" is an illusion -- simultaneity does not exist across vast distances.

Two events that appear to be simultaneous to an observer in motion (at a significant fraction of LS) will not be simultaneous to a stationary observer.

Time slows as you approach the speed of light, so time can in effect be thought of as expanding at the speed of light from all points.

That's why thinking of time as just another dimension, like width, breadth and depth, is a little misleading. Time is always moving at LS.

 

[MostlyHarmless]

Once again “now” is no more indefinable within physics than “here” is, but “only one "now" shared by all of us” is specifically indefinable within physics because of the relativity of simultaneity. Again if you think not then physically define this “only one "now" shared by all of us”, if you can’t then you need to rethink your concept of “only one "now" shared by all of us”.

I think the reason it is hard to grasp that we do not share the same "now" is one of scale. Our "nows" are very close to each other because basically we, the human race, are in the same place. Taking in the scope of the Universe, we are as much in the same here as we are in the same now.

Perhaps, if we sometime spread to the stars, we will come to have a more intuitive grasp on the fact that my "now" is not the same as your "now", if we are a thousand mm apart or a thousand light years.

 

[The Man]

I think the reason it is hard to grasp that we do not share the same "now" is one of scale. Our "nows" are very close to each other because basically we, the human race, are in the same place. Taking in the scope of the Universe, we are as much in the same here as we are in the same now.

Perhaps, if we sometime spread to the stars, we will come to have a more intuitive grasp on the fact that my "now" is not the same as your "now", if we are a thousand mm apart or a thousand light years.

Yep, and also because of the comparatively slow velocities we generally experience. Were we to be regularly zipping about at relativistic speeds like some elementary particles then I doubt this would be of any concern.

Personally I find knowledge of how the universe works to be quite rich, meaningful and satisfactory even if it is about something I don’t experience in everyday life or could never possibly experience. I am however truly sympathetic for those like Zeph who might be seeking something they would consider “richer or more meaningful” and hopefully satisfying. However this is the wrong place to look for that (being the math & science sub forum) if you don’t find the just the math and science of it enough to quench that thirst.

Sure my now is more important to me as is my here, but that doesn’t make it the only now or here. Technically we can not say only one now that we all share is an illusion all we can say is that we just can’t physically define such a now. In the case of solipsism or idealism (brain in a vat or simulation) only one now that we all share may very well be the case, but that is philosophical discussion not one of math or science and better suited to the appropriate section of this forum. While I can certainly understand that some would find such a philosophical discussion of now “richer or more meaningful” and hopefully satisfying, unfortunately that, to me, would be the only illusion in this case.

 

[Zeph]

You need to address this issue to demonstrate that your remarks are indeed thoughtful.

(smile) I never claimed to be thoughtful myself; I was thanking others like yourself for their thoughtful contributions. And elsewhere for their patience and courtesy.

My basic question "why is there a 'now'" was about whether there was anything in hard science which addressed the phenomenon that humans experience as a "present time", or "now". Why should languages have a past, present and future tense, if time is a frozen river and it all exists "at once"?

One set of respondents tended to (briefly) describe "now" as some variant of being the changing point between past and future. That's the concept I was trying to reconcile. Another set of respondents tended to describe (at somewhat more length) that kind of special "now" as an illusion which doesn't exist in science, or perhaps is even impossible. Some have addressed this by separating physics from metaphysics or philosophy, putting the common cnocept of "now" into the latter category.

In trying to elicit more depth from those who quickly dismiss the concept of "now" as a special moving point between future and past, I may have confused matters by bringing in "the shared now". This alas understandably brought into the discussion relativity and simultaneity. Despite superficial similarity, the concept I was invoking in terms of a "shared now" has to do with interactivity and consciousness which appear to reside at that junction between future and past, and the experience that we seem to all share that same junction. That is, the real or illusory splice between future and past seems to be at the same T value for all of us, give or take tiny relativistic effect but not give or take hours or days. Nobody's consciousness appears to reside a few hours ahead of the person sitting next to them, such that they are viewing the frozen river from a substantially different T. The person sitting next to me will experience the portion of the time axis labeled "the future" as starting at about the same T as I experience it. This experience is so universal and ubiquitous that I understand I may seem daft to some to even ask "where in physics is there any explanation for that?" - they literally cannot conceive of it in any other way so it needs to explanation and is immediately obvious.

The simultaneity of relativity refers to matching arbitrary t1 with t2, where it is completely irrelevant whether t1 is in the past or future; and I completely agree that such an arbitrary T is no more special than an arbitrary X. Indeed, the disparity between these "pick a t, any t, they are all alike" approach of physics, and the subjective experience which humans label "the present", was exactly my topic. Relativistic modifications of t as perceived from reference frame A, are very relevant to measurements along the t axis, but really do not apply to the question of why there appears to be a special splice point between future and past.

I take responsibility for having been so incautious as to let these concepts be conflated in the discussion, through allowing my "shared now" to be confused with simultaneity.

I did get some good responses. Basically, the physics oriented folks have explained away any concept of "now" or "future" or "past" (by which I mean the portion of the t axis labeled as future or past, not the mere direction) as either illusion or just too fuzzy to define in physical terms that can be meaningfully measured or discussed in physics. I basically agree with them on that. It appears to be impossible to even define in physical terms the concept of "now" as the point between past and future. The inability for me to create such a definition has to some degree been thrown in my face to indicate the fuzziness of my thinking, which amuses me greatly, given that my basic premise is that science appears to have no handle on the concept of "now" or "the present" or "the past" or "the future". That is, I began with the assertion that the concept of "now" appears to be outside the scope of hard science (and being open to reasoned contradiction).

My not being able to give a good scientific definition of "now" (including a shared now) is hardly refutation of my initial postulate. (chuckle) Coming up with a good scientific explanation for the universally experienced human "illusion" of past and future and present WOULD have been a counterpoint (and a welcome one; my assertions were not dogma, but starting points for a discussion in which I hoped the assertions would be countered).

When I have a bit more time, I'll look up the more recent scientific american article, tho. That sounds like the closest I've heard.

Again, thanks to everyone for their thoughtful contributions, and for their courtesy and patience.

Zeph

 

[Zeph]

Personally I find knowledge of how the universe works to be quite rich, meaningful and satisfactory even if it is about something I don’t experience in everyday life or could never possibly experience. I am however truly sympathetic for those like Zeph who might be seeking something they would consider “richer or more meaningful” and hopefully satisfying. However this is the wrong place to look for that (being the math & science sub forum) if you don’t find the just the math and science of it enough to quench that thirst.

Just to clarify a little - I put the question here because I was hoping that somebody could refer me to some real scientific theory which explains the near universal illusion that there is a past and a future and a "now" in between those. I find that particular illusion (of living in "present time") far more powerful than counting angels on the head of a pin, in fact just as powerful - albeit different - as the perception of living with three spatial dimensions. The more "scientific" the explanation, the better it would fill this gap I perceive between my largely rationality oriented approach to the universe and my own experience as a conscious being.

I'm not totally against some philosophical answers, but I am more wary as I have found that absent the reality-feedback mechanism of science, it's unfortunately easy for philosophy to invent elaborate intellectual rococco which mostly consists of increasingly self-referential complexity and clan recognition symbols (eg: the portion of jargon which serves more to delineate who is part of the clan than to functionally advance the discourse) rather than useful insight. That's just a judgment call I make in observing the universe, not a fact.

I realize that it may be uncommon enough here to be confusing, but my intention was NOT to push some theory as correct and defeat all opponents; my "assertions" were meant as starting points, not end points to be defended. Any resistance I have shown to various responses has been because I want the admittedly difficult-to-explain question I'm asking to be understood and addressed in its fullness, not because I'm vested in the initial assertions being correct.

I went through a similar quest at one time asking people the far simpler question of "why does a mirror reverse left and right but not up and down?" Why do we write "ambulance" reversed left/right rather than up/down if we want it to be visible correctly in the rear view mirror? I got answers like "gravity changes how light reflects" or "because our eyes are side by side", or "it's a psychological illusion" and I explained why those were not satisfactory answers to my question not because I thought it had to be unexplainable, but because I was looking for a deeper or more accurate answer (that inherently being my own judgment call of course).

Besides getting a good understanding of the mirror effect in question, I learned a lot about psychology. Some of the unreasonable answers came from people who are generally skeptics; what I found as that as soon as they came up with something plausible in their own minds, they were comfortable dismissing the question. At some level, the accuracy of the answer was less important than the relief of tension from something akin to cognitive dissonance. I found the relatively scientifically oriented folks were not much different in this regard; they tend to pull explanations out of a different bag, but below that level their motivations of seeking comfortable cognitive equilibrium with the universe were often very similar.

Very, very few were motivated to review their own first explanation and pick apart the problems with it to look deeper. For most, all that was needed was a kind of "plausible deniability" to the premise that there was a common phenomenon which they didn't really understand.

Being human, I'm mostly wired the same way, but I appear to have a somewhat larger than usual curiosity and self-reflection factor. And that's what prompted this thread, not a need to validate some existing theory as correct. That's the level to understand what I mean by "rich, meaningful or satisfying". I got some satisfaction from this thread, and would have gotten even more if I had heard some new approach to connecting the scientific view and the subjective "now".

Cheers,
Zeph

 

[RussDill]

That is, the real or illusory splice between future and past seems to be at the same T value for all of us, give or take tiny relativistic effect but not give or take hours or days. Nobody's consciousness appears to reside a few hours ahead of the person sitting next to them, such that they are viewing the frozen river from a substantially different T. The person sitting next to me will experience the portion of the time axis labeled "the future" as starting at about the same T as I experience it.

And again, I'm not really seeing why your question is special. You've only made now special and shared by saying that your now is equated to someone else now by it having the same T, and them OMG, why do all our nows have the same T?

To me, I don't really see the past as no longer existing, just as Disneyland still exists even though I'm not there right now. So your concept of now is very unspecial as your whole life you've believed it was now, and you've always been right. So has everyone else.

According to someone living on January 5th, 1885, Mark Twain exists in the same now. And also according to those who live 125 light years from us depending on interpretation or those who are traveling relativistically in respect to the earth depending on other interpretations.

In summary, its really just a discussion about consciousness. Being conscious, you are always aware of "now" and its relation to past and future events, its just part of self awareness, although, some people have neurological damage that destroys that.

The Wikipedia page on the present is particularly helpful, and it categorizes your question under "Philosophical problems"

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

 

[case#46cw39]

The simultaneity of relativity refers to matching arbitrary t1 with t2, where it is completely irrelevant whether t1 is in the past or future; and I completely agree that such an arbitrary T is no more special than an arbitrary X. Indeed, the disparity between these "pick a t, any t, they are all alike" approach of physics, and the subjective experience which humans label "the present", was exactly my topic. Relativistic modifications of t as perceived from reference frame A, are very relevant to measurements along the t axis, but really do not apply to the question of why there appears to be a special splice point between future and past.

Any real moment on the time dimension was at some time a future T, then a present T happening now, and then will also be a past T. SO there are no moments of time that are inherently now or past or future.

My basic question "why is there a 'now'" was about whether there was anything in hard science which addressed the phenomenon that humans experience as a "present time", or "now".

If you agree that to study and know time by definition is to address past events, present events, and future events, then you must agree with me that hard science has addressed it. And hard science has deeply developed the spacetime idea:

"In physics, spacetime (or space–time; or space/time) is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space being three-dimensional and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions. According to certain Euclidean space perceptions, the universe has three dimensions of space and one dimension of time. By combining space and time into a single manifold, physicists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels."
http://en.wikipedia.org/wiki/Spacetime

Thus either you think hard science understands spacetime but not what "now" means, which I can't accept, or you agree here is where science sees "now".

 

[The Man]

(smile) I never claimed to be thoughtful myself; I was thanking others like yourself for their thoughtful contributions. And elsewhere for their patience and courtesy.

I'm sure such thanks are welcomed, as I welcome it, but you must address specific issues raised in addition to just thanking people.

My basic question "why is there a 'now'" was about whether there was anything in hard science which addressed the phenomenon that humans experience as a "present time", or "now". Why should languages have a past, present and future tense, if time is a frozen river and it all exists "at once"?

One set of respondents tended to (briefly) describe "now" as some variant of being the changing point between past and future. That's the concept I was trying to reconcile. Another set of respondents tended to describe (at somewhat more length) that kind of special "now" as an illusion which doesn't exist in science, or perhaps is even impossible. Some have addressed this by separating physics from metaphysics or philosophy, putting the common cnocept of "now" into the latter category.

Again with "now" as the origin (always T=0) it is the ordinal values of other points in time that must change. Any point can be used as a partition or boundary separating two domains without any common members and can be included in one of those domains (closed/half closed) or not (it is its own closed or half closed domain).

In trying to elicit more depth from those who quickly dismiss the concept of "now" as a special moving point between future and past, I may have confused matters by bringing in "the shared now". This alas understandably brought into the discussion relativity and simultaneity. Despite superficial similarity, the concept I was invoking in terms of a "shared now" has to do with interactivity and consciousness which appear to reside at that junction between future and past, and the experience that we seem to all share that same junction. That is, the real or illusory splice between future and past seems to be at the same T value for all of us, give or take tiny relativistic effect but not give or take hours or days. Nobody's consciousness appears to reside a few hours ahead of the person sitting next to them, such that they are viewing the frozen river from a substantially different T. The person sitting next to me will experience the portion of the time axis labeled "the future" as starting at about the same T as I experience it. This experience is so universal and ubiquitous that I understand I may seem daft to some to even ask "where in physics is there any explanation for that?" - they literally cannot conceive of it in any other way so it needs to explanation and is immediately obvious.

Again, while it is easily understandable that your "now" is special to you, just as your "here" is, that does not make it special to anyone else or special in any physically definable sense. As noted by schrodingasdawg before physics is specifically formulated to be applicable to all "nows" and "heres".

The simultaneity of relativity refers to matching arbitrary t1 with t2, where it is completely irrelevant whether t1 is in the past or future; and I completely agree that such an arbitrary T is no more special than an arbitrary X. Indeed, the disparity between these "pick a t, any t, they are all alike" approach of physics, and the subjective experience which humans label "the present", was exactly my topic. Relativistic modifications of t as perceived from reference frame A, are very relevant to measurements along the t axis, but really do not apply to the question of why there appears to be a special splice point between future and past.

Again "now" is simply a arbitrary boundary between domains labeled as "past" and "future" .

I take responsibility for having been so incautious as to let these concepts be conflated in the discussion, through allowing my "shared now" to be confused with simultaneity.

Well I appreciate that you take that responsibility but I still think your are looking in the wrong place for the type of answer you appear to be seeking.

I did get some good responses. Basically, the physics oriented folks have explained away any concept of "now" or "future" or "past" (by which I mean the portion of the t axis labeled as future or past, not the mere direction) as either illusion or just too fuzzy to define in physical terms that can be meaningfully measured or discussed in physics. I basically agree with them on that. It appears to be impossible to even define in physical terms the concept of "now" as the point between past and future. The inability for me to create such a definition has to some degree been thrown in my face to indicate the fuzziness of my thinking, which amuses me greatly, given that my basic premise is that science appears to have no handle on the concept of "now" or "the present" or "the past" or "the future". That is, I began with the assertion that the concept of "now" appears to be outside the scope of hard science (and being open to reasoned contradiction).

No, "any concept of "now" or "future" or "past"" have not been "explained away" it is just that the mathematical and physical explanations are apparently not the ones your appear to be specifically seeking.

My not being able to give a good scientific definition of "now" (including a shared now) is hardly refutation of my initial postulate. (chuckle) Coming up with a good scientific explanation for the universally experienced human "illusion" of past and future and present WOULD have been a counterpoint (and a welcome one; my assertions were not dogma, but starting points for a discussion in which I hoped the assertions would be countered).

Your "now" is special to you just as everyone else's is to them, but no "now" is physically anymore special then another. That is simply how physics is formulated.

When I have a bit more time, I'll look up the more recent scientific american article, tho. That sounds like the closest I've heard.

Again, thanks to everyone for their thoughtful contributions, and for their courtesy and patience.

Zeph

You're welcome.

 

[The Man]

Just to clarify a little - I put the question here because I was hoping that somebody could refer me to some real scientific theory which explains the near universal illusion that there is a past and a future and a "now" in between those. I find that particular illusion (of living in "present time") far more powerful than counting angels on the head of a pin, in fact just as powerful - albeit different - as the perception of living with three spatial dimensions. The more "scientific" the explanation, the better it would fill this gap I perceive between my largely rationality oriented approach to the universe and my own experience as a conscious being.

Again mathematically "now" is just an arbitrary boundary between domains labeled as "past" and "future".

I'm not totally against some philosophical answers, but I am more wary as I have found that absent the reality-feedback mechanism of science, it's unfortunately easy for philosophy to invent elaborate intellectual rococco which mostly consists of increasingly self-referential complexity and clan recognition symbols (eg: the portion of jargon which serves more to delineate who is part of the clan than to functionally advance the discourse) rather than useful insight. That's just a judgment call I make in observing the universe, not a fact.

However those " philosophical answers" seem to be specifically the ones you're seeking as the mathematical and physical ones don't appear satisfactory to you.

I realize that it may be uncommon enough here to be confusing, but my intention was NOT to push some theory as correct and defeat all opponents; my "assertions" were meant as starting points, not end points to be defended. Any resistance I have shown to various responses has been because I want the admittedly difficult-to-explain question I'm asking to be understood and addressed in its fullness, not because I'm vested in the initial assertions being correct.

I went through a similar quest at one time asking people the far simpler question of "why does a mirror reverse left and right but not up and down?" Why do we write "ambulance" reversed left/right rather than up/down if we want it to be visible correctly in the rear view mirror? I got answers like "gravity changes how light reflects" or "because our eyes are side by side", or "it's a psychological illusion" and I explained why those were not satisfactory answers to my question not because I thought it had to be unexplainable, but because I was looking for a deeper or more accurate answer (that inherently being my own judgment call of course).

If I recall correctly you also got the answer that a mirror simply reverses the ordering of points along an axis normal to its surface.

Besides getting a good understanding of the mirror effect in question, I learned a lot about psychology. Some of the unreasonable answers came from people who are generally skeptics; what I found as that as soon as they came up with something plausible in their own minds, they were comfortable dismissing the question. At some level, the accuracy of the answer was less important than the relief of tension from something akin to cognitive dissonance. I found the relatively scientifically oriented folks were not much different in this regard; they tend to pull explanations out of a different bag, but below that level their motivations of seeking comfortable cognitive equilibrium with the universe were often very similar.

"dismissing the question"? Perhaps, but more likely just considering the question being satisfactorily answered for them, just as you are here seeking an answer you find satisfactory, but again I think your are looking in the wrong place for the type of answer you would appear to find satisfying.

Very, very few were motivated to review their own first explanation and pick apart the problems with it to look deeper. For most, all that was needed was a kind of "plausible deniability" to the premise that there was a common phenomenon which they didn't really understand.

Being human, I'm mostly wired the same way, but I appear to have a somewhat larger than usual curiosity and self-reflection factor. And that's what prompted this thread, not a need to validate some existing theory as correct. That's the level to understand what I mean by "rich, meaningful or satisfying". I got some satisfaction from this thread, and would have gotten even more if I had heard some new approach to connecting the scientific view and the subjective "now".

Cheers,
Zeph

While I can't speak for those others or on that particular thread (as I didn't read much of it after a physically accurate answer was given) I can say that you need to seek whatever satisfies you and not presume that others should look for or provide you with whatever you might consider to be " deeper" that are not so engaged. Again I would direct you to the philosophical section of this forum as that appears to be the type of satisfaction and 'depth' you are seeking.

Good luck in your search

Dan "The Man"

 

[dogjones]

There is no such special t, either. Conscious being existed in the past, and (hopefully) will exist in the future as well.

I think you've mis-identified the fundamental distinction between time and space. "Now" is analogous to "here", and there's nothing especially mysterious about it. "Now" and "here" are simply where and when you as you express those words.

Strikes me that as well as "where" and "when" there could also be a "which" (thanks Sheckley). i.e. where do all the possible but non-actual "nows" stand?

 

[Zeph]

Regarding mirrors reversing left/right rather than up/down...

While I can't speak for those others or on that particular thread (as I didn't read much of it after a physically accurate answer was given) I can say that you need to seek whatever satisfies you and not presume that others should look for or provide you with whatever you might consider to be " deeper" that are not so engaged. Again I would direct you to the philosophical section of this forum as that appears to be the type of satisfaction and 'depth' you are seeking.

Just to clear something up - I asked my mirror question in person years ago, back when I lived in a Colorado university town - not here. I think you may be suggesting that there was a similar thread here, but if so I have not seen it.

I also just discovered that there is a Zephyr and a Xephyr registered here - neither are aliases of me (or appear to hold the same opinions).

As to the mirror question, that does make a decent illustration. That a mirror reverses one axis is not really much of an answer answer (perhaps in the thread this was embedded in a richer answer). Ironically a fuller answer DID involve psychology and gravity. My own answer would have been something like -

The word "Ambulance" is actually not "reversed left/right" when you see in in the rear view mirror - it has been in effect visually moved forward such that it appears to be as far in front of the mirror as it actually is behind the mirror (that inverting of one axis from the mirror surface). However humans are psychologically "biased" by living in a gravity field, in regard to their choice of rotation axes; in many ways we live in a 2D world. If we were to wish to "turn around" to look directly at the "Ambulance" sign, we are far more likely to rotate our heads or bodies around the axis parallel to gravity than to turn ourselves upside down. If we did the latter, the "Ambulance" sign would indeed be reversed up/down rather than left/right. This physical preference for rotating around the gravity vector results and a mental bias towards more easily grasping or assuming that rotation in interpreting the universe aroudn us. If we had always floated in free fall without gravity there might not be that bias (it would be an interesting experiment). So the apparent "left/right" vs "up/down" reversal doesn't in the end have to do with the mirror, but with our preferential axis of rotation when viewing the world and the resulting mental models. The mirror didn't reverse it left/right, it is we who tend to reverse it left/right when we turn to view it directly (or even imagine how we would do so).
​

I would find that an example of a "deeper" answer to the question than just "mirrors reverse one spatial axis", yet I don't consider it purely "philosophical". And the thread here may have come to a similar explanation, I do not know. This does illustrate one of the types of answers I would have found satisfactory - not just describing the math of timelines or mirrors, but addressing and explaining the seemingly disparate subjective human experience.

AND - I agree, it looks like in the case of now/past/future, there may be only philosophical answers rather than hard science one. Even in that case, I am more interested in the kinds of philosophical answers which are rampant within quantum physics, than those which might appear in a typical new age blog, or even most academic philosophical discourses.

Zeph

 

[Lithrael]

Sorry for the derail but...

If we were to wish to "turn around" to look directly at the "Ambulance" sign, we are far more likely to rotate our heads or bodies around the axis parallel to gravity than to turn ourselves upside down. If we did the latter, the "Ambulance" sign would indeed be reversed up/down rather than left/right.

That doesn't follow. It'd have to be rotated 180 degrees and flipped left to right to be readable in a mirror if you were used to looking at things behind you upside down.

ETA: clearly I am on crack, as these are the same things. Nevermind.

 

[The Man]

Regarding mirrors reversing left/right rather than up/down...



Just to clear something up - I asked my mirror question in person years ago, back when I lived in a Colorado university town - not here. I think you may be suggesting that there was a similar thread here, but if so I have not seen it.

My apologies then as I simply assumed you were referring to another discussion on this forum, (which unfortunately I can’t seem to find now).

I also just discovered that there is a Zephyr and a Xephyr registered here - neither are aliases of me (or appear to hold the same opinions).

As to the mirror question, that does make a decent illustration. That a mirror reverses one axis is not really much of an answer answer (perhaps in the thread this was embedded in a richer answer). Ironically a fuller answer DID involve psychology and gravity. My own answer would have been something like -

The word "Ambulance" is actually not "reversed left/right" when you see in in the rear view mirror - it has been in effect visually moved forward such that it appears to be as far in front of the mirror as it actually is behind the mirror (that inverting of one axis from the mirror surface). However humans are psychologically "biased" by living in a gravity field, in regard to their choice of rotation axes; in many ways we live in a 2D world. If we were to wish to "turn around" to look directly at the "Ambulance" sign, we are far more likely to rotate our heads or bodies around the axis parallel to gravity than to turn ourselves upside down. If we did the latter, the "Ambulance" sign would indeed be reversed up/down rather than left/right. This physical preference for rotating around the gravity vector results and a mental bias towards more easily grasping or assuming that rotation in interpreting the universe aroudn us. If we had always floated in free fall without gravity there might not be that bias (it would be an interesting experiment). So the apparent "left/right" vs "up/down" reversal doesn't in the end have to do with the mirror, but with our preferential axis of rotation when viewing the world and the resulting mental models. The mirror didn't reverse it left/right, it is we who tend to reverse it left/right when we turn to view it directly (or even imagine how we would do so).
​

I would find that an example of a "deeper" answer to the question than just "mirrors reverse one spatial axis", yet I don't consider it purely "philosophical". And the thread here may have come to a similar explanation, I do not know. This does illustrate one of the types of answers I would have found satisfactory - not just describing the math of timelines or mirrors, but addressing and explaining the seemingly disparate subjective human experience.

AND - I agree, it looks like in the case of now/past/future, there may be only philosophical answers rather than hard science one. Even in that case, I am more interested in the kinds of philosophical answers which are rampant within quantum physics, than those which might appear in a typical new age blog, or even most academic philosophical discourses.

Zeph

Well it is up to you to clarify what is you are looking for in terms of the context of this section of the forum and unfortunately “deeper” is still rather ambiguous.


Mathematically “now” can just be a point (though it does not have to be) and thus have no temporal extent itself.

Physically or scientifically we may find that time is discrete and only applicable in whole units of Planck time (in some given reference frame), thus a physical “now” might need to have some temporal extent itself.

Technologically “now” could be the difference in time between some input and the resulting output of some device or the resolution in units of time of some measuring or metering device (still limited by the possible extent of some physical “now”).

In terms of medicine or more precisely physiology “now” could be the difference in time between some stimulus and our resulting reaction. Even more so if you include the requirement of consciousness (the time for you to become aware of some reflex reaction). In that aspect our perceptions extend into (what would mathematically or physically be called) the past and our actions into the future (with awareness of some actions even being preceded by that action). So this is really the worst case scenario for “now” as not only is it limited to longer expanses of time than the other three considerations but that time expanse can also vary from one “now” to the next and from one set of conditions or subjects to the next, even to magnitudes that we can perceive directly ourselves.


I think the last one might be the “now” you are interested in and I think we have already established that “now” can be defined objectively, mathematically and physically but also that one now shared by all of us can’t. It seems that particular ascription is no longer of concern to you. So now I’m not sure what it is that you are inquiring about “now” and if you have any unanswered questions it would be helpful if you could put them in terms applicable to the context of this section of the forum.

 

[Zeph]

Mathematically “now” can just be a point (though it does not have to be) and thus have no temporal extent itself.

Physically or scientifically we may find that time is discrete and only applicable in whole units of Planck time (in some given reference frame), thus a physical “now” might need to have some temporal extent itself.

Technologically “now” could be the difference in time between some input and the resulting output of some device or the resolution in units of time of some measuring or metering device (still limited by the possible extent of some physical “now”).

In terms of medicine or more precisely physiology “now” could be the difference in time between some stimulus and our resulting reaction.

Smile. I'm not understanding how defining "now" as one of these delta-T's is very helpful. It has been a given from the start that there are small "fuzzy" difference in how we perceive "now".

It's so fascinating to me to see this question through two lenses at once. One lens is very much like yours - I too don't see any real significance to the concept of "now" in physics. In the other lens, I see the concept of "now" as fundamental to our experience of the universe, as significant as anything else we perceive (even if hard to measure meaningfully in scientific terms). That disparity is exactly what prompts the question. It would be cool to have some more convergence, and maybe one day that will happen.

I've enjoyed the chance to refine my own understanding by contrast to some of the sharp minds here. Various explanatory approaches have occurred to me and I've tried them, with interesting results, even when letting myself get sidetracked.

Let me try one more which popped into my head. Since you like delta T, how long ago, or how far into the future, is 2am Wednesday morning Jan 12, 2011 PST, as you read this? For me it's 4 minutes ago as I write, but will be different later. Is that concept meaningful to you? If so you are measuring the time difference between (1) a fixed time, and (2) something else. What is that something else? If there is no special "now" time because any moment is or has been a now just like any other, then how can you measure the time between a fixed point and "now" and get one answer rather than an infinite number of equally plausible answers?

Yes, I know, it's just like "here" and the distance from "here" to the statue of liberty. Except as you read this sentence, the time delta has changed, because your "now" point changed position in a predictable way along the time axis. For both of us. And if I call you on the phone, we'll both agree, within some fraction of a second due to relativistic, mechanistic, quantum, and physiological factors, on the difference in time from 2011-01-12 02:00:00 PST and the "now" we both happen to arbitrarily pick out of a time continuum where no point is different than another. And if we talk roughly a day later, we'll again agree that by great coincidence, both of us have again chosen to experience an arbitrary "now" point the same number of hours "since" 2011-01-12 02:00:00 PST.

That is what I mean by a shared now. It's not precise, but it's also not arbitrary. When we communicate in what we call "real time" with only minor delays, we happen to pick the same number of minutes since a fixed time as our shared "here" on the time axis.

We will both say "it has been 12 hours and 22 minutes since T0"; even if we would disagree at the nanosecond level, neither of us on the phone call is going to say "that's 6 hours in the future" or "that was three years ago". The point on the time axis which we label as "now" moves at close to the same rate for each of us. And we cannot do anything to stop, slow, or reverse that increasing time delta between T0 and what we call "now" (or decreasing time delta if T0 were in the future).

Physics is great at "it took 3 hours to melt" or "it will take 3 hours to melt", but there is no real concept of "3 hours ago" in physics, because that would measuring time relative to a meaningless point on the t axis. You all have reinforced that concept very well. Yet we human find "3 hours ago" a very meaningful and even useful concept, just like "next week".

The closest I've come so far to finding to a physical explanation seems a little bit weak, at least to my understanding. Much of physics considers that the only assymmetry to explain the arrow of time is entropy, but as far as I've followed that discussion so far it is more like "it must be due to entropy because we don't have any other assymmetry as a candidate, but we don't know how it works and cannot measure it".

We can "perceive" - albeit imprecisely - the past because it has less entropy, but not the future because it has much entropy. This is intriguing and I'll keep reading about it. I do not really find it sufficient however. Look at how assymmetric it is - we can "perceive" or measure or record information from billions of years into the past, but not even a nanosecond into the future. Is the entropy of every local frame really increasing that fast? Can anybody show me how Shannon's equations account for this degree of assymmetry?

Once we see that physics really does not (yet) seem to have much handle on explaining the difference between "future" vs "past", we see that it also has no real handle on "now" as the changing junction between those - the moving point on the timeline where the incredible entropy of the future (which blinds us) becomes the manageable entropy of the past (which we can "remember" or measure).

I regret that I let the conversation drift into things like relativistic time frames, and I appreciate the patience of those like yourself who tried to clue me in as to why a precise "shared now" is not possible (which I already knew, but you were not aware of that so you get credit). I did not have all this very well thought out yet (and I realize you are probably convinced I still have no clue

But we were talking about different levels of precision in defining "shared". You are correct that even when at rest relative to each other we are incapable of agreeing on the meaning of any arbitrary time point ("now" or "then") to infinite precision, due to speed of light delays, time quanta, and perhaps physiological delays of milliseconds. That's a truism of a sort - in the sense that I'll also grant that there is no truly meaningful single time which is exactly 2011-01-12 02:00:00 PST. So it's only in a very practical but relativistically meaningless that we can ever give meaning to any timestamp.

I'm referring to the fact that when we talk with each other, we can speak of "yesterday" as if we were talking about the same day - as if "my now minus around hours" somehow relates meaningfully to "your now minus around hours", despite both "now" either being illusions or arbitary.

It's almost as if we were on the same time elevator, and both defined "now" as approximately the same T, rather than each independently picking an arbitrary T for our personal "now" which is in no way distinguished from any other T. But I see nothing in physics which could explain why we'd be on the same elevator - why our "now" would stay roughly in sync even as our "here" doesn't. Relatively does explain why our "now" can never be precisely in sync, but I'm seeing no explanation for why my "now" shouldn't be completely different and not even vaguely correlated to yours, similar to my X,Y,Z.

Pointing out that relativistically we can't have an exact shared now is about as relevant to what I'm saying as explaining to your spouse that exactly 2pm on Saturday is impossible to define given relativity, so you can't be late for a meeting at that time. It's true in some sense, but misses the point.

Zeph

 

[Michael C]

I don't think the relativity argument misses the point. When considering time as a dimension, it can help to use the same units for time and distance. We might chose seconds, for instance: a second of distance is the distance light travels in one second. Using only one unit can give us a better sense of proportion between time and space. We tend to think of something on the other side of the world as very far away, whereas we think of something that happened a second ago as very close. If you use seconds for both time and space, you'll see that something that happens on the other side of the world can be closer than something that happened a second ago.

In fact our "here"s are as close as our "now"s: anybody near you in the space-time continuum will be experiencing almost the same "now" and "here" as you do. The further somebody gets away from you, whether it be far in time, far in space, or both, the more difference there can be between their "now" or their "here" and yours. We have shared "now"s only when we have shared "here"s.

"3 hours ago" is only unambiguous for somebody near you in both time and space. If I heard a recording of you saying "3 hours ago", I could only know what point in time you were referring to if I were told when you said it. It so happens that we both live on Earth, so I can safely assume that you were not far away in space when you made the recording. If we could possibly be separated by light-hours or even light-years, I'd also need to know where you were when you said it.

 

[The Man]

Smile. I'm not understanding how defining "now" as one of these delta-T's is very helpful. It has been a given from the start that there are small "fuzzy" difference in how we perceive "now".

It is often helpful to determine the limits or extents of some consideration and if it can or indeed must have some particular extents. I’m not sure what constitutes a “small "fuzzy" difference” but it just seems a way of dismissing any difference by labeling them as “small” and/or “fuzzy”, particularly when the differences can be quite specific and even large enough to be ascertainable by our own rather “fuzzy” perceptions.

It's so fascinating to me to see this question through two lenses at once. One lens is very much like yours - I too don't see any real significance to the concept of "now" in physics. In the other lens, I see the concept of "now" as fundamental to our experience of the universe, as significant as anything else we perceive (even if hard to measure meaningfully in scientific terms). That disparity is exactly what prompts the question. It would be cool to have some more convergence, and maybe one day that will happen.

Now is a significant concept in physics, it is when things happen between what has happen and what may/will happen and again it is just one now which we all share that has no significance in physics. Do you still perceive your “now” as such or have you in fact rescinded that requirement as your pervious post indicated?

I've enjoyed the chance to refine my own understanding by contrast to some of the sharp minds here. Various explanatory approaches have occurred to me and I've tried them, with interesting results, even when letting myself get sidetracked.

Let me try one more which popped into my head. Since you like delta T, how long ago, or how far into the future, is 2am Wednesday morning Jan 12, 2011 PST, as you read this?

I’m not sure what you think “like” has to do with it and I have certainly never expressed any preference for a now that has some temporal extents over one that does not. However science is quantitative so one way of scientifically exploring and comparing different concepts of “now” is looking at how they may differ, well, quantitatively.

Currently it is 16:02 EST Jan 12, 2011. You can do the math if you actually need or would like a delta T.

For me it's 4 minutes ago as I write, but will be different later.

So you got a different answer and will have another different one later. Will there ever be a “now” forthcoming where you won’t have a different answer than before?

Is that concept meaningful to you?

I’m not sure what concept you are referring to? That you will have a different answer (to some degree accuracy) each time you ask what is essentially the question ‘what time is it now?’?

If so you are measuring the time difference between (1) a fixed time,

Yes the fixed time you gave..

“2am Wednesday morning Jan 12, 2011 PST,”

and (2) something else.

Yes the answer to your question which was basically what time was it for me as I read you question.

What is that something else?

The time that I read your question, 16:02 EST Jan 12, 2011, another fixed time once I did read your question.

If there is no special "now" time because any moment is or has been a now just like any other, then how can you measure the time between a fixed point and "now" and get one answer rather than an infinite number of equally plausible answers?

Because the “one answer” is only between two fixed points in time.

The time that I am replying to this question is 16:11 EST Jan 12, 2011, another answer and fixed point in time that you can apply to your previously given “2am Wednesday morning Jan 12, 2011 PST,”. Just as you will get a different answer each time you ask just yourself ‘what time is it now’.

Yes, I know, it's just like "here" and the distance from "here" to the statue of liberty. Except as you read this sentence, the time delta has changed, because your "now" point changed position in a predictable way along the time axis.

Predictable? Well today has been anything but predictable, so you’ll have to excuse me for a while…

OK I’m back, it is “now” 20:55 EST Jan 12, 2011, sorry about that, but as unpredictable as that delay was, had I been traveling at varying relativistic speeds or in some intensely varying gravitational field it could have been even more so. Even if we had synchronized our watches at the first time and agreed I’d be back in four of my (or your) hours.

For both of us.

Nope, again your four hours need not be mine nor mine yours, I’m not sure why you keep glossing over this fact.

And if I call you on the phone, we'll both agree, within some fraction of a second due to relativistic, mechanistic, quantum, and physiological factors, on the difference in time from 2011-01-12 02:00:00 PST and the "now" we both happen to arbitrarily pick out of a time continuum where no point is different than another. And if we talk roughly a day later, we'll again agree that by great coincidence, both of us have again chosen to experience an arbitrary "now" point the same number of hours "since" 2011-01-12 02:00:00 PST.

While we certainly could agree and our originally synchronized clocks could still be synchronized after some period of time in one of our reference frames, neither ourselves nor our clocks are required to remain in such an agreement. You seem to be operating under the impression that these “relativistic, mechanistic, quantum, and physiological factors” must all amount to some “fraction of a second” that you can simply dismiss as your small "fuzzy" difference.

That is what I mean by a shared now. It's not precise, but it's also not arbitrary. When we communicate in what we call "real time" with only minor delays, we happen to pick the same number of minutes since a fixed time as our shared "here" on the time axis.

It is arbitrary as we can use my reference frame or yours as some frame of reference and your shared now is simply not physically definable as we need not (and in some cases won’t) agree on the “same number of minutes since a fixed time".

We will both say "it has been 12 hours and 22 minutes since T0"; even if we would disagree at the nanosecond level, neither of us on the phone call is going to say "that's 6 hours in the future" or "that was three years ago". The point on the time axis which we label as "now" moves at close to the same rate for each of us. And we cannot do anything to stop, slow, or reverse that increasing time delta between T0 and what we call "now" (or decreasing time delta if T0 were in the future).

Well that’s the rub of it Zeph, I might well say I’m just 6 more hours into my future while it was three of your years ago that we last talked. Time is relative, that point still seems to be escaping you.

Physics is great at "it took 3 hours to melt" or "it will take 3 hours to melt", but there is no real concept of "3 hours ago" in physics, because that would measuring time relative to a meaningless point on the t axis. You all have reinforced that concept very well. Yet we human find "3 hours ago" a very meaningful and even useful concept, just like "next week".

What makes you think "3 hours ago" isn’t a useful concept in physics. If physics says "it took 3 hours to melt" then it also says that the temporal measurement started, well, "3 hours ago".

The closest I've come so far to finding to a physical explanation seems a little bit weak, at least to my understanding. Much of physics considers that the only assymmetry to explain the arrow of time is entropy, but as far as I've followed that discussion so far it is more like "it must be due to entropy because we don't have any other assymmetry as a candidate, but we don't know how it works and cannot measure it".

Ever hear of Spontaneous symmetry breaking? Though it is still related to increasing entropy, much like the fixed point in time once the question “what time is it now” is answered; similarly the probability of some outcome is 100% once that outcome has occurred. What might have been a symmetrical probability of outcomes has become the asymmetrical result. Just as when asked what time it is "now" earlier I gave an answer that was earlier than that that was the answer to the same question later.

We can "perceive" - albeit imprecisely - the past because it has less entropy, but not the future because it has much entropy. This is intriguing and I'll keep reading about it. I do not really find it sufficient however. Look at how assymmetric it is - we can "perceive" or measure or record information from billions of years into the past, but not even a nanosecond into the future. Is the entropy of every local frame really increasing that fast? Can anybody show me how Shannon's equations account for this degree of assymmetry?

That would be a limitation of our perceptions; the universe is not bound by our perceptions. Check out Wheeler-Feynman absorber theory. Physically “now” could be as much of the past as it is the future.

Once we see that physics really does not (yet) seem to have much handle on explaining the difference between "future" vs "past", we see that it also has no real handle on "now" as the changing junction between those - the moving point on the timeline where the incredible entropy of the future (which blinds us) becomes the manageable entropy of the past (which we can "remember" or measure).

You keep making such assertions and claim “that physics really does not (yet) seem to have much handle on explaining the difference between "future" vs "past", then give an example of such a physical distinction between "future" vs "past", changing entropy but still seem unsatisfied by such a physical distinction. Again this leads me to believe that what you are looking for really is an answer in more of a philosophical basis.

I regret that I let the conversation drift into things like relativistic time frames, and I appreciate the patience of those like yourself who tried to clue me in as to why a precise "shared now" is not possible (which I already knew, but you were not aware of that so you get credit). I did not have all this very well thought out yet (and I realize you are probably convinced I still have no clue

Sorry but you still don’t seem to be aware of it as you still seem to be trying to posit that notion. Oh, I think you have a clue and that might be the problem you don’t seem that interested in a philosophical discussion (as well I can understand) but that seems to be the type of answer you might find more satisfying.

But we were talking about different levels of precision in defining "shared".

Physically define your “shared” “now” to any precision that suits you.

You are correct that even when at rest relative to each other we are incapable of agreeing on the meaning of any arbitrary time point ("now" or "then") to infinite precision, due to speed of light delays, time quanta, and perhaps physiological delays of milliseconds. That's a truism of a sort - in the sense that I'll also grant that there is no truly meaningful single time which is exactly 2011-01-12 02:00:00 PST. So it's only in a very practical but relativistically meaningless that we can ever give meaning to any timestamp.

I have never said anything about some “infinite precision”. Define the physical or other constraints you want to work under and we can discuss your “now” under those constraints. If not then the comparatively unconstrained philosophy of now may be what you are seeking. However mathematically (as a point) with no time expanse itself “now” would be, well, infinitely precise.

I'm referring to the fact that when we talk with each other, we can speak of "yesterday" as if we were talking about the same day - as if "my now minus around hours" somehow relates meaningfully to "your now minus around hours", despite both "now" either being illusions or arbitary.

Your yesterday could be my last year, in spite of your regrets about the relativity of time it is a highly relevant issue to any discussion of “now” and a demonstrable occurrence.

It's almost as if we were on the same time elevator, and both defined "now" as approximately the same T, rather than each independently picking an arbitrary T for our personal "now" which is in no way distinguished from any other T. But I see nothing in physics which could explain why we'd be on the same elevator - why our "now" would stay roughly in sync even as our "here" doesn't. Relatively does explain why our "now" can never be precisely in sync, but I'm seeing no explanation for why my "now" shouldn't be completely different and not even vaguely correlated to yours, similar to my X,Y,Z.

Almost, but it isn’t, we do not have to be “on the same time elevator” and to some degree of precision we aren’t, just because we might be on the same floor now does not mean we are on “the same time elevator”. We can pick “an arbitrary T for our personal "now"” even pick some arbitrary method for measuring T which is only distinguished from any other T by being my or your T.

Pointing out that relativistically we can't have an exact shared now is about as relevant to what I'm saying as explaining to your spouse that exactly 2pm on Saturday is impossible to define given relativity, so you can't be late for a meeting at that time. It's true in some sense, but misses the point.

Zeph

Again I’ll keep pointing out the relativistic (and other) aspects as long as you seem to keep missing them. Time is relative; your perception is unreliable compared to available instrumentality. What you perceive as instantaneous or “now” occurs over some expanse of time that varies to degrees that you could even perhaps perceive yourself if you just weren’t so, well, “fuzzy” out those differences.

 

[sol invictus]

...

You still haven't succeeded in identifying a relevant difference between "now" and "here". You have many examples in your post that are supposed to indicate how we "share a common now" or how "now" is special, but all of them work just as well for "here".

The only true asymmetry is that time has an arrow - and even that may be an local artifact.

 

[Perpetual Student]

The only true asymmetry is that time has an arrow - and even that may be an local artifact.

What does that mean? How could the arrow of time be a "local artifact," since the whole universe seems to be uniformly aging? Could there be any piece of the universe that is not 13.7 billion years old like the rest? Or -- are you saying some piece of the universe could be getting younger as we are experiencing our local here and now ?

 

[sol invictus]

What does that mean? How could the arrow of time be a "local artifact," since the whole universe seems to be uniformly aging?

It's not uniform (for example, those parts in gravitational potential wells age more slowly), although of course none of the part we can see is getting younger!

Could there be any piece of the universe that is not 13.7 billion years old like the rest?

That actually is the case taking into account small variations - but they are indeed fairly small (except near strongly gravitating objects like black hole horizons).

Or -- are you saying some piece of the universe could be getting younger as we are experiencing our local here and now ?

That's a possibility, yes. Another is that either in the far past or the far future of our own piece the arrow was pointing the other way.