Kevin's Watch

If I could add one sentence to Richard Feynman's famous one in which, in one sentence he transmits as much information to a future generation that has lost all knowledge of the nature of the universe in which we live as is possible (that stuff is made up of individual particles, being his chosen one), it would be that "Now is only now, here."

This is the central core of Einstein's Special Theory of Relativity - that the instant of now that we all experience (with the past stretching out behind us and the future extending out before) is entirely relative to our own particular position. The duration of the 'now instant' extends with distance away from the observer, such that on say the surface of Mars it is (from our position) about fifteen minutes in length. This means that to talk of 'now' on the surface of Mars, from here on Earth, you are actually refering to a period of about fifteen minutes.

As the duration of now increases relative to our position on Earth, it encroaches into the past and future, such that (presumably) at some distance the entirety of time is encapsulated in the now (again, from our own perspective, it must be stressed). Going back to Mars, the 'now' for the individual on the surface of that planet seems as instantaneous as ours does for us, but looking Earthward our now would seem to him (or her) to be same fifteen minutes that his appears to us.

Assuming I have this correct, and given that we can calculate this increase in the duration of 'now' with respect to increasing distance, what I want to know is this. What is the distance at which the entire existence of the universe, past and present, is caught up in our 'now'? Is it at the furthest limit of the observable universe, or the universe proper? Or does it occur before that point, say somewhere in the depths of space? Is this distance always the same - or does it increase as the universe expands?

Come on you lot; step up to the plate and nail your colours to the mast! Let's be having it!

You know you can do it!



(Vraith - where are you when we need you? )

peter wrote:This is the central core of Einstein's Special Theory of Relativity - that the instant of now that we all experience (with the past stretching out behind us and the future extending out before) is entirely relative to our own particular position. The duration of the 'now instant' extends with distance away from the observer, such that on say the surface of Mars it is (from our position) about fifteen minutes in length. This means that to talk of 'now' on the surface of Mars, from here on Earth, you are actually refering to a period of about fifteen minutes.

Are you sure you have that right? I would think that 'now' on Mars is fifteen minutes in the past. But how can now extend for 15 minutes of duration?

Never mind the thermodynamic complications of being able to see the future.

peter wrote:Assuming I have this correct, and given that we can calculate this increase in the duration of 'now' with respect to increasing distance, what I want to know is this. What is the distance at which the entire existence of the universe, past and present, is caught up in our 'now'? Is it at the furthest limit of the observable universe, or the universe proper? Or does it occur before that point, say somewhere in the depths of space? Is this distance always the same - or does it increase as the universe expands?

This is complicated by the fact that the universe is expanding. The farther into the past you go, the smaller the universe is, and so the "edge" is closer to us. In the extreme past, the universe is a point and everything is co-located. However, the closer the edge gets, the more recent is it's 'now'. So in essence you have two conflicting phenomenon - the farther away it is, the more into the past we can see, and the the more into it's past we can see, the closer it is.

Well it's an odd one to be sure WF, but in pursuit of getting it right I'll quote a few lines from the book I'm reading by Carlo Rovelli, a theoretical physicist working in the field of quantum gravity and author of the book (from which I quote) Reality is not what it seems.

Between the past and future of an event ( for example, between the past and future for you, where you are in the precise moment in which you are reading) there exists an 'intermediate zone', an 'extended present'; a zone that is neither past nor future. This is the discovery made with special relativity.

The duration of this 'intermediate zone' (the set of events at a space-like distance from a reference event), which is neither in your past or your future, is very small and depends on where an event takes place relative to you: the greater the distance from you, the longer the duration of the extended present. At the distance of a few meters...... the duration of what for you is the intermediate zone, neither past nor future, is.... a few nanoseconds. On the other side of the ocean....a thousandth of a second. But on the moon the duration of the expanded present is a few seconds, and n Mars it is a quarter of an hour. This means we can say that, on Mars, there are events that in this precise moment have already happened, events that are yet to happen, but also a quarter of an hour during which things occur that are neither in our past nor in our future.
They are 'elsewhere'. We had never before been aware of this 'elsewhere' because next to us [it] is too brief; we are not quick enough to notice it. But it exists and it is real.

These are the words from the book WF, pretty much verbatim (with a little bit of the padding removed). They are accompanied by a diagram of a guy sitting in a chair reading a book, time on the vertical axis and distance on the horizontal (he sits in the middle, as it were, of the graphical field) Above his head is labelled 'future' and below him 'past' (he sits in a grey band which in a previous "space and time before Einstein" diagram had been labelled 'present', but in this one now contains two black cones/triangles extending out from him along the distance axis direction in both directions, labelled 'the extended present'. (Sorry this is a bit cumbersome as descriptions go.)

From all of this I read the implication that present is not a fixed duration event that occurs simultaneously no matter where you are in the universe, but rather is a variable duration event, the duration of which is entirely dependent upon the observers position and extending in magnitude with increasing distance? Am I reading this right, do you think?

(Edit; Another 'insight' which I have gained from my reading last night is that there is no such thing as 'space' {or more correctly space-time} in the way I understood it. I (like many others I suspect) had been thinking of space as a thing in which the 'fields' that carried electromagnetic waves etc existed in. This had always perplexed me. What exactly were these fields? What were they made of? Now, from my reading, it transpires that space-time and these fields are one and the same thing. From Einstein's next theory, that of General Relatively, it transpires that space-time is the gravitational field; there is no space in which they 'are situated' - it is the field/s themselves (I include the electromagnetic field here, correctly or otherwise) that are what we had previously referred to as space (space-time). And it is ripples and bending of this field that causes the effects that we see as gravity. This subtle distinction, that it is space itself that is the field and not a case of the field existing within space makes it much clearer to me (and also deals with the 'action at a distance' problem that Newton grappled with, but was never really able to reconcile in his theory of gravitation. Now there is no action at a distance because we have a medium we can quantify, express mathematically, that connects all bodies in our universe. There is no 'space with fields and matter within it' - only fields and particles; this is the sum of our universe.)

I don't think you're reading it wrong.

But I for one have no clue what it implies. And I suspect neither do you.

If "the present" is 15 min on Mars to people on Earth but instantaneous to people on Mars, what does this mean? It means that it is an issue of perception and information, not of time distortion. The whole point of relativity is that things look different depending on where you are. So this is a things-look-different scenario.

It sounds to me like this phenomenon is describing a kind of Schrodinger's cat phenomenon, describing a zone in which we cannot measure precisely when something occurred. Or, more accurately, within this "intermediate zone", an occurrence happens at all times at once, but as time moves forward the occurrence moves out of this zone and into the past, which "opens the box", there is a quantum collapse, and now we can measure precisely when it happened.

Which seems to have no practical implications. We cannot "see" anything happening on Mars until long after it has occurred. We cannot sense in any way that 15 minutes of present.

And even if we could sense something so far away at instantaneous speed, the act of observing would "open the box" as well.

Yes, I think you have grasped it better than me straight away. There is a bit in the book, following the quote I gave that I think says pretty much what you have just said - let me just see if I can find it........

This is why it is impossible to hold a smooth conversation between here and Mars. Say I am on Mars and you are here. I ask you a question and you reply as soon as you've heard what I've said; your reply reaches me a quarter of an hour after I posed the question. This quarter hour is time that is neither past nor future to the moment in which you've replied to me. The key fact about nature that Einstein grasped is that this quarter of an hour is inevitable; there is no way of reducing it. It is woven into the texture of the events of space and time; we cannot abbreviate it any more than we can send a letter to the past.

I'm struggling to get my head around this; every time I think I'm getting it, it slips away, eel-like, from my comprehension!

peter wrote:This quarter hour is time that is neither past nor future to the moment in which you've replied to me.

I don't follow this, either. Clearly this time comprises the 7.5 minutes before I replied and 7.5 minutes after I replied. I know exactly where it is in respect to past and future.

Now, it's true that you are unaware of the question for 7.5 minutes until it arrives, and after you reply, you don't have to wait 7.5 minutes while the reply flies back to Mars. Maybe the author is trying to make something of this. But I am not sure what.

However, if you were to have an actual conversation with someone on Mars, a back and forth consisting of more than one utterance on each side, you would become keenly aware of the 15 minute delay!

It's one of those situations (I get them a lot in books like this) where you just have to take it as read and plough on. Still - I'm not going to beat myself up about it too much. After all, the reason why Einstein got it and I don't is quite simple; he was Einstein and I'm not!