I am looking for some help with understanding an aspect of physics which relates to something I want to consider theologically.
Basically, it is to do with the question of existence and time.
There’s a rather nice diagram which, I gather, sums up the present state of understanding in terms of time and space.
Here, the past is ‘the region from which we can receive light’ and the future is ‘the region to which we can send light’.
Thus the longer ago a thing happened, the further the distance from which we can receive light from that event. Hence, the ‘past’ light cone contracts towards us, the observer, in the present, as we can only receive light from recent events that are correspondingly near to us in space, whereas we can receive the light of events that took place billions of years ago from equally immense distances away.
On the other hand, if we point a flash gun at the sky and set it off, the light will spread out (theoretically) throughout the universe, so the ‘future’ light cone expands away from us. After eight minutes it will have reached the Sun. After about four and a half years, it will have reached Alpha Centauri, and so on.
What I am really interested in, however, is that bit of the diagram labelled “hypersurface of the present”, and what the relationship is between ‘the present’, ‘the past’ and ‘the future’.
And here’s my key question: how can we speak of things that are not on the hypersurface of the present actually existing?
It would seem patently obvious (though I may be missing something!) that from a simply physical point of view, nothing on the ‘future’ side of the diagram actually exists at all, even if its ‘coming into being’ is both predictable and inevitable.
Does the same, however, apply to the past? If so, then the only realm in which we can talk about things actually existing is on the plane of the hypersurface of the present.
But then we have to ask the question, just how ‘thick’ is that plane? I believe some people suggest it is just a ‘Planck Moment’, but I’d be interested to know of other ideas.
I am aware that the question is complicated by aspects of Relativity theory, which mean that time is not ‘absolute’. In particular, there is the interesting, though hard to conceive, fact that events which appear simultaneous to one observer may be separated in time from the perspective of another observer.
Considered overall, then, the hypersurface of the present may be ‘wavy’ — a bit ahead for some observers, a bit behind for others, but how far might these ‘waves’ extend?
I am also aware that St Augustine of Hippo wrote a whole chapter on this subject in his Confessions. What he said is very interesting, but I’m trying to get at the physics in the first instance before looking at the theology.
What I am asking is whether it could actually be that, despite our memories of the past and our anticipation of the future, what exists, physically, is confined to a ‘micromoment’.
Thoughts and contributions would be welcome.
John Richardson
14 December 2010
Anonymous users wishing to paste in the comments box need first to select 'preview', then close the preview box. When posting your comments please give a full name and location. Comments without this information may be deleted.
14 December 2010
My comments may seem overly obvious, but what Augustine was getting at is that time is most important, but it is a commodity like any other. Past, present and future are as tangible as anything. As proof, he points out our concepts of distance, space and interval.
ReplyDeleteHe also draws a comparison with "eternal" in which time is neither short or long, not a commodity at all. Indeed, time is a created substance. It is not a part of a world that might be called eternal. Augustine goes on to explain that God in Christ was (or is) "before all worlds", outside of time, and yet He comprehended it fully by entering it as a man.
The eternal is an essential ingredient to the present, affecting it in every detail, but there is no reciprocity... the present (or past or future) has no contingent effect whatsoever on the eternal. I don't think your diagram works too well in a world now enlightened by Quantum Mechanics, which has demonstrated the limits to refusing to see beyond the temporal, that insists upon making sense of things using only man's ability to measure time, distance, mass, and energy.
Just to throw another question into the mix John, suggest you take a look at
ReplyDeletewww.imprint.co.uk/pdf/smythies.pdf
The idea here is that there is a physical relationship between time and consciousness. That moments in time are never 'lost'.
I'm inclined to think this is probably true. I am currently putting together an essay on the relationship between time, consciousness and the Calvinist idea of predestination for the course I am doing at my local Baptist College.
Interested to see what other people think here.
Chris Bishop
Devon
I think it's a bit more complex than that. Events which are neither in the definite future nor the definite past light cone are neither past nor future. The shape (and angle) of the "hypersurface of the present" depends on the speed and direction at which you are travelling...
ReplyDeleteSo when you say "what exists?", you raise the question "from whose point of view", because it's different from different positions and at different velocities.
Of course, it seems easiest to say that from God's point of view, he sees the lot of it - past, future and unknowable present.
If you want more complexities, try throwing in the Einstein Podolsky Rosen Paradox / Action at a Distance...
John Allister (MSci), Cheshire
One reason Physicists use Maths such a lot is that words often have imprecise definitions. You ask if "something can exist outside of the present" but "exist" is in the present tense, so how long is that defined as? It is possible of course, for something to have existed, be existing and continue to exist into the future - in which case it will have a "shape" occupying both of your cones and the "plane" of the present time.
ReplyDeleteI think the plane in your diagram is a personal "plane of perception" rather than a manifestation of real space-time and so will be be unique to each observer. That gets over your problem of relativity and wavy-ness.
So I would say that both the past and the future "exist" it is just that we cannot perceive them.
But I always thought God existed outside of time in a more profound way than this. God created space-time, so he is outside time in the same way that he is outside of all his creation.
But then I am just an amateur.
I've sent a link of this to a Christian friend of mine who works for NASA, in the hope she can shed some light on it. I don't think it's within her day job, but I suspect to her it will be basic stuff! I can't promise she'll have time to reply though.
ReplyDeleteDavid Wilkinson of St John's Durham gave the annual Bishop of Sheffield's Shrove Tuesday lecture this year and I suspect is the person to give you a well informed answer. He did mention his latest book, which may be relevent:
http://www.amazon.co.uk/Christian-Eschatology-Physical-Universe-Wilkinson/dp/0567045463/ref=sr_1_1?ie=UTF8&s=books&qid=1292377311&sr=8-1
The hypersurface is simply the projection of three-dimensional space into two-dimensions, purely for the purpose of depicting time as a third dimension. Whether the hypersurface actually has thickness depends on the concept of granularity of time, but that's a completely difference issue - for our purposes, we can consider the hypersurface to a be a plane, i.e., it has no thickness.
ReplyDeleteThe question of whether anything exists that isn't on the hypersurface of the present ducks the more important question of whether anything exists on that hypersurface other than the observer. We can only ever know anything about the existence of any event if it is actually on the cone of past light (where it would be perceived as happening "now") or within that cone. As for things outside of that, we may be able to come up with probabilities that something may or may not exist, and sometimes those probabilities will be close to 1 or 0, but we can never be certain about them existing until our movement through time causes an event to pass through and into our cone of past light.
Relativistic effects are not represented by any kind of distortion in the hypersurface of the present. Each observer has their own position in space and their own cones of future and past light. If a specific event occurs at a particular point in space and time, the point at which that event passes through the cone of past light (and is thus perceived as occurring "now") for two different observers may well happen when those two observers are at different places along the time axis. If a second observer is moving relative to the first you start to see relativistic effects such as time dilation. In the extreme case, where an observer is moving at the speed of light, a single event perceived as momentary to other observers can be seen as taking place continuously and eternally by the (impossibly fast) observer.
You can actually use the geometry of these light cones to derive the special relativity equations.
I have absolutely no idea what any of this tells us about God, other than that he certainly knows how to make an interesting universe for us to admire and puzzle over.
Thank you for all the comments so far. I hope I still have your attention, because I am really trying to get a grip on this!
ReplyDeleteI get the basic points being made about different observers observing events differently, but I’d like to focus on just two phenomena — an event and an observation of the event.
Take, for example, a flash of light — the emission of a burst of photons at point A. They are emitted, and off they go. That is 'the event' in this case.
Now I would presume this means that the configuration of particles which constituted A before the photons were emitted changes upon their emission. This may (or may not!) be theoretically reversible (ie, if you ran the tape the other way it would still, technically, ‘work’), but actually things don’t ‘go into reverse’.
Then, as time passes (as we say), the photons get further from A. They don’t suddenly turn round and go back towards A, and even if they did, they could already have been detected at point B (at a different location from A).
Is, then, what we call the ‘passage of time’ reducible to a series of different physical configurations?
And if it is then does not time ‘vanish’? But then do not the other physical configurations also ‘vanish’, leaving just the configuration existing 'right now' (whatever 'now' is - which is my point)?
BTW I think on of the 'complicating' factors is that when we talk about 'an observer' we seem to imply a conscious observer. But 'an observer' need be nothing more than, say, a light detector (for the purposes of describing the phenomena involved).
Can replies be couched in these terms — where a light detector would detect the photons emitted from point A — rather than ‘what an observer would see’?
PS, I seem to recall St Augustine speaking about time 'vanishing' in this way, but I'd rather keep theology out of it for the moment, until I know what I'm supposed to be theologizing about.
For me, James67 has said it all! Especially helpful is his point that the hypersurface is so called because it is not a surface as we normally meet them, but a "projection of three-dimensional space into two-dimensions, purely for the purpose of depicting time as a third dimension." Its thickness might suggest to us that existence is fragile, the blink of an eye; but of course that present moment is continually moving in time, and represents all our known universe, with the observer at the centre.
ReplyDeleteJohn - I'm not sure if I'm reading you correctly.
ReplyDeleteDoes your question reduce to something like this?:
Does the past still exist, or is it gone for good?
If so, the answer to that question depends rather pedantically on your definition of existence and tense rather than on physics.
In English, the past does not continue to exist. But it might in Hebrew!
Ian, I wonder what you would understand by the phrase "moving in time". What moves? And what do you mean by "in", as in "moving in time". See my earlier comment about time as a series of physical configurations.
ReplyDeleteJohn, the short answer is 'Yes'. But I still want to get at the physics. Again, see my earlier comment about physical configurations. Is the 'passage of time' reducible to a sequence of physical configurations of which only one is ever 'actual'?
PS I am pressing these points not to show anyone is wrong, but because I don't necessarily understand them!
Interesting questions! It's quite a while since I thought about these things, but I wonder if the Heisenberg uncertainty principle might have something to say here. I am wondering what you mean by a physical configuration? The Heisenberg uncertainty principle seems to state that if one knows precisely the position of everything, then one cannot know its momentum. In other words a snapshot of the physical configuration of everything at a given time is impossible.
ReplyDeleteThis may have something of a bearing on your questions relating to the vanishing of time. I know that's not really answering them directly, but perhaps it will catalyse some other ideas?
John Percival
John P, I think I'm right in saying that Heisenberg refers specifically to certain sub-atomic particles. In other words, you can know very precisely both the momentum and the location of a bus if you step in front of it.
ReplyDeleteHowever, even those things whose momentum and location cannot be simultaneously detected nevertheless have a simultaneous momentum and location.
Thus although a snapshot of everything everywhere cannot include its detection, everything is nevertheless 'somewhere' and (theoretically) detectable.
John,
ReplyDeleteThanks for quick response. Heisenberg refers to sub-atomic particles because on that scale the issues of uncertainty in detecting location and momentum have a more significant role than in the case of a bus. However, I would contest your statement that such particles possess a simultaneous momentum and location, even if it cannot be detected. My understanding of quantum physics is that it operates on the basis of probability. When operating on the scale of a bus, the probabilities are so vanishingly small so as to be inconsequential. But when trying to make a comprehensive snapshot of everything, such probabilities would be important. What I think Heisenberg tells us is that there is no one snapshot of the present configuration, but rather a range of different snapshots of varying probabilities. A particle does not possess a simultaneous momentum and location, because that particle is also a waveform. If your snapshot pins down the precise location then it cannot also pin down the precise momentum and therefore is not a complete snapshot of everything.
I am getting into deep waters here, but I found the Wikipedia page on Heisenberg to be of some value.
From a Christian, and not a scientific, point of view, this is all rather simple!
ReplyDelete1. Although I accept that some Christians think that 'millions of years ago' did exist I don't. So that part is dealt with.
2. As to the future, we believe that Jesus Christ will come again, and that such a coming may happen at any moment - whether that be now, next week or next millenia. So how could we possibly "send" something to a 'time' that may never take place? We can't. End. !
Hello, there does seem to be a lot of confusion here.
ReplyDeleteThe diagram is a variation of the 'Minkowski' diagram, which represents 4-dimensional space-time onto a 2-dimensional piece of paper.
The vertical axis is 'Time'. To say that something on the 'future side' doesn't exist is meaningless. It simply has not happened yet, and might never happen.
If something has happened in the past we may or may not know about it. As I write, the Sun has just exploded, but that event is outside of my light cone, I will live for another 8.5 minutes.
Quantum physics (Uncertainty, Heisenberg etc) is great fun, but not relevant here.
Kevin_K
Rev Dominic, thanks for that, but actually the same question presents itself, as far as my interest goes, regarding five minutes ago - or even five seconds, or five milliseconds ago.
ReplyDeleteThe question is: what is the status of that which then 'existed'? Does it still 'exist' or is that the wrong way to think about the past - and ditto the future?
Kevin (sorry about the momentary confusion with Dominic, but you probably didn't notice), when you say something "simply has not happened yet", that's what I mean by "doesn't exist", and when you add "and it might never happen", that's also what I mean by doesn't exist (not the same as couldn't).
ReplyDeleteSimilarly, something which a data detector could theoretically detect does "exist".
I agree Heisenberg is simply a diversion.
John (Richardson): James67's answer is spot on.
ReplyDeleteI have on engineering based degree and one theological and I think that the diagram is not that helpful in answering your question and is confusing matters. Seems to be some confusion on the role of light.
If your question is as the other John stated it: Does the past exist? then the answer is yes - actually all we observe is past events delayed by the passage of light.
Kevin_K poses a good point - that you will not know the sun had exploded (or to clear the argument: disappeared) for 8.5 minutes. The Earth would continue to go round the non-present Sun. How ever if you were a 'being' that occupied the area of the sun and Earth simultaneously you would have knowledge of that would happen 8.5 minutes in the future for the Earth.
Now if you were an omni-present being in all areas of the universe you would see all time as one as well. Hence from a relativity point of view God, who is in all places, must also be in all time. Apply that to pre-destination.
Ben
Ok, I'll drop Heisenberg... Let me explore something else:
ReplyDeleteSuppose, John, you lived on Alpha Centuri, 4 1/2 light years away. Does my two year old son, born on earth exist, from your point of view? Your data detector on Alpha Centuri can only detect that which is within the past light cone centred on Alpha Centuri. And therefore from your point of view, my son's birth in 2008 is undetectable and therefore does not exist. The only earth accessible to you on Alpha Centuri at the end of 2010 is the earth of mid-2006. So in a sense it seems that the past does continue to exist. But I cannot get from earth to Alpha Centuri quickly enough to overtake the past and experience it 'arriving' at Alpha Centuri.
John
PS I just spotted Ben's post and think his second paragraph is making a similar point
John Percival, thanks for this, but I'm still having problems.
ReplyDeleteI think the introduction of light years of distance is itself obscuring the point I’m wrestling with - though I’ll take the blame for that, as I think I raised it first. (In fairness, it seems usually these matters seem to be discussed in ‘astronomical’ contexts.)
However, let’s just think about the hypothetical 'you' on earth watching your son being born. In the infinitesimal, but finite, period of time it takes for the light to cross the distance between your wife’s bed and you, would it be fair to say his birth “is undetectable and therefore does not exist”?
Technically, the answer would have to be ‘no’ if the birth of your son is undetectable until the sensory impression of his birth reaches you.
To test this, I would ask, “What if you were a bit further away, down the corridor? What if you were abroad and having to watch it online? What if you were on a vital trip into space, out in the orbit of Jupiter? At what point in this extrapolation does one switch from ‘common sense’ “Of course he exists” to ‘counter-intuitive’ “He doesn’t exist til the light reaches me”?
In other words, does the introduction of big distances really change the picture at all?
Thanks John. You're right that there's a difference between what exists at any given moment, and what I can detect exists at any given moment. The former is the 'hyperspace of the present' and the latter is the surface of the 'past light cone'.
ReplyDeleteBut I think I've lost track of the nub of the issue with which you're wrestling. If you want to, perhaps you could help me by restating it?
Ben,
ReplyDeleteThanks for your response, but as in John’s case, I’m still struggling with the reply.
You wrote, “If your question is as the other John stated it: Does the past exist? then the answer is yes - actually all we observe is past events delayed by the passage of light.”
Now that being the case, if we think in terms of detector D and transmitter T separated by space S, what D is detecting and what T is transmitting are always different.
The shorthand for this is, “It takes time for the signal from T to reach D” and “By the time the signal reaches D from T, T will be sending out a different signal.”
In actuality, though, it seems that what we could say is, “The configuration at any given moment M is that the signal from T is at S(M1), S(M2), S(M3) and so on, whilst D is in condition D(M1), D(M2), D(M3) and T is in condition T(M1), T(M2), T(M3).”
We can conceive of what an observer at D would observe, and what an observer at T would observe. And we can also conceive, and describe, the whole scenario.
Now if the signal takes three ‘moment configurations’ to reach D from T, we would say D detects the condition of T as it was ‘three moments ago’ (call it T-3). But it would seem that the actual configuration of T itself at T-3 is not recoverable. In that sense it “doesn’t exist”, even though it certainly once “existed” (ie T has had that configuration).
So the ‘past’ of T is an unrecoverable configuration of T which is nevertheless detectable by D. What we donot have, however, is an ongoing configuration of T in that state which D detects after the necessary ‘moments’ for the signal to pass from T to D.
John - I'm in serious danger of getting confused myself! What I'm trying to get a handle on is how we can speak of material existence in temporal terms, and therefore what we mean by saying something 'exists'.
ReplyDeleteThere is a danger when we move to the macro-level, as we are seeing in this discussion, that we start applying different fundamental principles to 'very far off' or 'very old' events, when I am presuming they ought to apply to 'very near' and 'very recent' events as well. (Ie, there is no discontinuity between the two which kicks in at a certain time or distance.)
If I can sort this out, I want then to consider the nature of experience, which it seems to me may perhaps create an illusion that 'the present' is a measurable period.
But I don't want to go there til I've got a handle on the initial question.
Thanks for helping to clarify things. A number of points come to mind, though I'm not sure how directly they answer your question:
ReplyDeletePast states of the universe are indeed irrecoverable - the second law of thermodynamics states that entropy never decreases, and I am think I am right in saying that in the case of the whole universe the reality is that it is always increasing. Therefore it would be impossible to recover an earlier configuration of the universe without external input - ie God!
The two cones, past and future, are also causality cones - the event horizon. My experience of causality is limited to that which lies within the cones. I can only be affected by that which lies within my past time cone, and I can only affect that which lies within my future time cone. The advantage of looking at large distances is that they allow us to take into account the speed of light as the limit of causality.
I think the example of the sun mentioned earlier in this thread could be helpful. Is the sun yellow right now? As far as I am concerned, even if it actually turned blue 2 minutes ago, from my point of view it is yellow. It will be a further 6 minutes until my past time cone comes to contain where the sun is now, assuming that I do not move. Of course if I flew towards the sun then I could discover that it had turned blue sooner than if I stood still. Also, if I started accelerating away from the sun and continued accelerating then it would be possible for me never to know that it had turned blue. I need never know that the sun turned blue. As long as I keep on accelerating, the sun will always be yellow and not blue.
The hyperplane of the present is inaccessible to the finite observer. What exists depends on where you are making your observations. I will only be able to tell if something exists if its future light cone intersects with my future light cone. The sun example I gave above is a case when the two light cones do not intersect.
But I think you are right in saying that the past does not exist in any real measurable sense. All I know of a past event is the impact that the event has had on the space between that event and me over the course of time. So sitting on the earth, I do not know the sun turned blue, strictly speaking, but only that I received some blue light from the space that lies between the sun and me. From that I extrapolate that the blue light was emitted by the sun, and therefore 8 minutes ago the sun must have turned blue. The past does not exist. All I can do is to recall what I experienced at some point in the past. I speak from the point of view of a finite observer. From God's point of view, I suspect that every moment is equally vivid and real, and therefore that time, past, present and future, exists simultaneously to him.
wikipedia defines "existence is the world we are aware of through our senses, and that persists independently without them".
ReplyDeleteI agree that the past cannot be revisited because the direction of time is defined by this process of irreversibilty, as John P describes.
You seem to be saying that the past does not exist because it does not persist - the idea that we cannot revisit it. I suppose I would have to concur with this.
The idea that existence is more closely related to our sensual experience of it, is I think, a distraction. The phenomena of relativity and uncertainty apply to the present observable universe (to what exists) and do not really help to answer your question about what persists.
Lesley and John Percival, thanks for that.
ReplyDeleteI think the notion of 'persistence' is a helpful clarification.
However (I bet you could see that coming), it is a basic question in philosophy as to what 'persists' of the world, when it is not being perceived.
Things like colour, taste, smell, texture, for example, are clearly 'realities'. It would seem pedantically odd to say that colour does not 'exist' (if, by this, we mean it is not a reality), but it does not 'persist' independently without being a sensory experience.
Still, for the moment I think we can sideline the question simply by focussing on the issue of time.
Here, however, it seems the 'observational delay' is also confusing us.
We understand 'scientifically' as it were that if the Sun turned blue right now, we wouldn't know for eight minutes. But to say that therefore it wouldn't 'exist' for us is, I think, a misuse of the word 'exist'.
Given that we know the time it takes for light to reach us from the Sun, we would simply say that, strictly speaking, we know what the Sun was like eight minutes ago, and in eight minutes time we shall know what the Sun is like now.
But in our minds we know there is a Sun-now and an earth-now configuration. The observational delay is just an aspect of that configuration. But it is the configuration itself which is the 'now' to which we refer.
The question is, therefore, not when does the light from the Sun reach the earth-bound observer, but when does the 'now' of any particular configuration become the 'then' of the past.
Just to keep everything in one place, I'm closing this thread and asking people to post future comments under the latest post on this topic, here.
ReplyDelete