The speed of *now*

[Cyperium]

Well, it turns out it isn't.

What "we" can prove is dependent on many things.

I am on Mars and you are on Earth. We are between 3 and 22 light minutes apart.

If I fire off a rocket here on Mars, I know whats gonig to happen in your future.

It gets even weirder if we are moving at relativistic velocities with respect to each other. I could go on a relativistic journey that only lasts a year for me and arrive back on Earth to visit you in your nursing home. Whose "now" are we talking about?

You don't know what is going to happen in my future, since if we are stationary relative to eachother my 'now' is also your 'now', I can't prove that you fired the rocket (since it would take me 3-22 minutes to know if I saw it through a telescope), but it isn't simply what I can prove that sets 'now', but instead what anyone can possibly prove. Do that between all reference points. It's not what I can prove or what you can prove, it is what can be theoretically proven as far as any reference point can prove that the future exists.

It still holds true though for the subjective perspective, my 'now' is the point where I personally can't prove my future exists. For all I know I can die this moment. But it also holds true of all reference points. That could be said to be 'now'. There is of course a limit to the extent that anything can be proven about the future. The sun, no matter what vantage point you are looking at it from, wouldn't have become a red giant. No matter the relative speeds or anything. There is a point where no future can be proven to exist. That point is 'now'.

 

[Cyperium]

There's a different arrangement of "all particles in the universe" in each Now -- with enough configurations (Nows) to exhaust all possible combinations of how the universe can exist. But nobody much takes it seriously or completely understands what Barbour is about. Yet his scheme is a kind of interesting twist to "Many Worlds". To where the meandering trail we experientially take through that manifold of static "parallel universe" like states constitutes our history (the countless changes or events of time). Go through it again, and it would be a different route, because there is no pre-set "railroad track" the changes follow. That's part of why he asserts that time does not exist.
_

Had me lol a bit when you ended my quote with /url, but anyway; in relativity, if I understand it correctly, the order of events must be preserved. This excludes 'all possible combinations' in each now (as far as I can tell), you would get all possible combinations that preserves the order of events (I guess that could be inferred by 'possible' as well though), but if we merge it with the 'many worlds' interpretation then of course anything is literally possible, and squared with that is in each possibility also all possible configurations that preserves the order of events, which is like 'many worlds' with 'many nows' or what you could call it I guess.

So the 'many nows' in his view, if I understand it correctly, is a higher dimension (even higher than time itself) where you can start at the beginning of the lower dimension (think ordinary spacetime), but you continue in the higher dimension of time (the "manifold of nows") so that the events unfolding are still unique and not repeated? Sounds a bit like that's what he's getting at? Could be, but I could also be completely lost in my trying of understanding his view.

 

[Cyperium]

I think that since you can make a one-to-one correlation between time intervals in different reference frames, you may be able to establish a universal now.

Yeah, I was getting that feeling as well. If you take all possible reference frames (with different speeds/accelerations) etc., then arrive at a point in which the furthest possible future exists which you can prove exists using all the reference frames available in the current universe. Obviously a task no one can actually do, but theoretically that should be where true 'now' is in time. The "edge of tomorrow" if you like. The existence of a new moment being created obscured by countless perspectives. Yeah, truly the breaking of a new dawn.

Reminds me of "The Langoliers" by Stephen King, when they finally arrive at the present moment and the world is reanimated in front of their eyes.
Ending Scene - The Langoliers

 

[TheVat]

Anyway, since he doesn't really get how the illusion of literally moving from one brain state to a different one (time "flowing") comes about in the worldline of a biological body in even a classical conception of spacetime... Then his efforts to explain why there "merely seems" to be an objective passage of time in his own (supposedly) "quantum-friendly" scheme has probably been a train wreck of futility.

Barbour fascinated me for a while, about 25 years ago. I recall him trying to frame the illusion through what he called "time capsules", which are "any fixed pattern that creates or encodes the appearance of motion, change or history". This puts us as conscious surveyors, in which our minds move across these landscapes which are a terrain of fixed slices of now whose adjacency depends on their similarities of pattern. The more similar, in Barbours universe, the closer they are. It's not a block universe, since it would lack any orthogonal time dimension or line, but closer to McTaggart's B series - indeed, reading Barbour it seemed to me that McTaggart is his primary influence. I can't recall all the criticisms that were fired at Barbour, except for Lee Smolin who is sort of the Great Anti-Barbour. Entertainingly so.

My own criticism was that, at the end of the day, I couldn't see what could be done with such a theory. It sort of landed on me the way Matrix theories do, i.e. "well great, so how does this really change anything for us if we're stuck in the illusion?"

 

[DaveC426913]

You don't know what is going to happen in my future, since if we are stationary relative to eachother my 'now' is also your 'now', I can't prove that you fired the rocket (since it would take me 3-22 minutes to know if I saw it through a telescope),

I know that you're going to see a rocket take off 3-22 minutus in your future.

but it isn't simply what I can prove that sets 'now', but

Right. That was my point.

It still holds true though for the subjective perspective, my 'now' is the point where I personally can't prove my future exists.

Right. Your now.
Not any kind of universal now.

For all I know I can die this moment. But it also holds true of all reference points. That could be said to be 'now'. There is of course a limit to the extent that anything can be proven about the future. The sun, no matter what vantage point you are looking at it from, wouldn't have become a red giant. No matter the relative speeds or anything. There is a point where no future can be proven to exist. That point is 'now'.

You really need to read up on the subject of the relativity of simultaneity.
It would vastly improve your notions on the matter.

 

[James R]

in relativity, if I understand it correctly, the order of events must be preserved.

That is not true, in general. It is possible to have situations in which, according to observer A, event X happens before event Y and also that according to a different observer, B, event Y happens before event X.

This is an extension of the result about the relativity of simultaneity, which says that there can be events that are simultaneous according to observer A but not simultaneous according to a different observer, B.

The failure to preserve a unique sequence of events throws a spanner in the works of any hypothesis that tries to draw a hard line between past and future. The fact is, past and future events are relative to the observer. (This is one reason for the name "Relativity".)

 

[James R]

Cyperium:

When considering how two people agree on the current moment, it seems that it depends on the speed of light.

No. It just depends on them synchronising their watches. However, it turns out that, if the two people are going to move relative to one another, they won't be able to maintain that synchronisation. Their watches will go "out of sync" when they move.

We don't notice this sort of thing much in our daily lives, however, because most of us don't flit around at large fractions of the speed of light. Far from it.

If I do any action *now* the information of that action will be transferred to any observer by the speed of light, so isn't it fair then to say that we differ on our perception of what is *now* by the time information travels from one person to another?

No, because we know how to account for signalling delays. We know what the speed of light is. So if we know that star X is 250 light years away and we suddenly see it explode, then we know that the light we just saw took 250 years to get from star X to us. We then conclude that, in fact, star X is not exploding now (when we see the explosion), but that it actually exploded 250 years ago and we're only just seeing the explosion now.

Now, if that is true, we could take it to the extreme, so that if someone is standing ~300 million meters away from me, his current moment is now 1 second in the past for me.

Not if his watch is synchronised with yours.

Look, the two of you can synchronise your watches before he leaves. Then, very slowly, he can move 300 million meters away from you, and his watch will stay approximately in sync with yours. After that, even though he is 300 million metres from you, you can both agree on what happened at 2 pm last Tuesday, in your specific locations.

Just as we have different locations in space, we also have different locations in time.

Relativity describes our motion through spacetime as a worldline. Suppose you stand still for 1 hour. In relativity, your worldline would be a straight line in spacetime, with constant position coordinates and a time coordinate that increases at 1 second per second.

The further away from me, the further in the past is the current moment for any other person, depending on how much time light have taken to reach that person.

No, because that person can do the maths on the signalling delay, as long as they know how far away from you they are.

If we take it to the ultimate extreme, the current moment of the Universe itself, must be the Big Bang or at least how far in time that light (thus information) has been able to reach us.

No. Because we can account for the time delay it has taken light from the big bang to travel to us from distant places in the universe, then appropriately back-date events that we are seeing now using light from far away.

If we don't regard relative motion at all, that must mean that everything is actually happening at the same time.

Well, yes. It means that if everything in the universe was stationary, then you could give people anywhere in the universe synchronised watches and they would all agree on the current time (and remain in sync).

The only seperation of times being due to relative motion.

Yes, and also acceleration, as it turns out.

I want to grasp the simpler idea of the current moment without the complexity of relative motion. Because that would help me understand why science says that there is no universal *now* and how *now* is propagating.

Let me know how you go understanding the explanation I have just given you about clock synchronisation and signalling delays. There are no bizarre relativistic effects involved in any of that. Just an understanding that the speed of light is finite.

So *now* isn't itself information?

"Now" is just a particular moment of interest on your watch. As soon as you see it, your time has moved on. (Actually, before you see it, because light has to travel from your watch to your eye.)

Perception is a valid measure of the universality of *now* though if we take it to large enough scales.

By "perception" do you mean observation and actual measurement (using a stopwatch, for instance), or do you mean something more like your fuzzy human feelings about time passing? The latter aren't a very reliable measure of the passage of time.

I still find it a bit confusing that any relative movement (maybe with acceleration) breaks the universality of *now* so that *now* in an accelerating frame could be different from my own *now*.

The reference frame doesn't have to be accelerating. Even motion at constant relative velocity will do the trick.

Time can move slower or faster, but the end of it, the current moment just seems to me to always be the same for everyone.

If I take a fast rocket trip to Alpha Centauri and back, in the process aging 2 years while you stay on Earth and age 10 years, then you'll have trouble trying to sustain the idea that "really" our respective experiences of time were the same.

Maybe the trouble is defining what a 'now' really is.

Relativity doesn't have trouble. For a particular observer - e.g. yourself - some events are in what is called your "past light cone" and some events are in what is called your "future light cone". Your past light cone contains all events in space and time that can possibly have influenced you in any way, including all the events you can possibly know anything about at this instant. Your future light cone contains all events in space and time that you can possibly influence by any action you take in the current instant.

In this picture, your "now" is a single point that lies between your past and future light cones. It contains all the events that are happening right where you are, at this exact instant in time.

Of course, 10 minutes from now, your past light cone will have expanded, because you will be able to receive signals, in principle, from 10 light minutes further away than you can now. Your future light cone will also have changed. And so will that single point between the two, that you want to call "now".

Also, it's important to realise that my light cone is not the same as yours, because we are not located at the same position in space. I can therefore know about things you cannot know about now. I can also influence certain things in the future that you cannot, and vice versa.

Cause we could say that all time exists at once, the past and the future, and that time is only an illusion by the brain, making 'now' a subjective experience and subjective only.

Events seem to happen irrespective of the presence of brains. (Although, this is philosophical question we could debate.) That suggests that time is not purely psychological, and certainly not an "illusion".

You have probably noticed that everything doesn't happen at once, for instance. That suggests to me that time is a thing. How about you?

 

[James R]

I think that since you can make a one-to-one correlation between time intervals in different reference frames, you may be able to establish a universal now.

Explain how you would make a "one-to-one correlation" of time intervals in different reference frames, please.

I can't tell what you're trying to say.

 

[Pinball1970]

This is all about the concept of simultaneity and reference frames which has been touched on
I think the guy on the train, guy on the platform and the lightning strikes illustrate it well.
The fact you can derive gamma (using lights and mirrors) shows it is not just conceptual but also mathematically consistent too.
Some physicists I have spoken to on the PF do not like it but it worked for me at the basic conceptual level.
It illustrates two things, the concept of "now" and or simultaneity are an illusion and time dilation.

Einstein worked this and Minkowsk is worth having a look at too. The diagrams may help you. Cyperium

 

[Pinball1970]

Einstein's train

 

[Pinball1970]

., then arrive at a point in which the furthest possible future exists which you can prove exists using all the reference frames available in the current universe. Obviously a task no one can actually do, but theoretically that should be where true 'now' is in time.

Just to add this is not something you can just visualise and talk out.
Just taking the speed of light to be constant makes no sense in our everyday life. You would never guess it, never philosophise or derive it, work it out using logic.
So your thought experiments regarding time will fail.

There is a stack of books on the subject and "Taylor and Wheeler" seems to be the preferred standard.
There are even more you tube videos some with, some without maths.

 

[Wizard of Whatever]

Explain how you would make a "one-to-one correlation" of time intervals in different reference frames, please.

I can't tell what you're trying to say.

Since each temporal interval can be represented by a real number line and any real number line has the same number of points (infinite) a conceptual one-to-one correspondence can be made between all intervals.

 

[QuarkHead]

Since each temporal interval can be represented by a real number line and any real number line has the same number of points (infinite) a conceptual one-to-one correspondence can be made between all intervals.

So the time until my next beer and the end of the universe are the same. Damn!

 

[Wizard of Whatever]

So the time until my next beer and the end of the universe are the same. Damn!

No, that is a misinterpretation. I'm considering in different reference frames.