# In the block universe, what makes this particular 'now' special?

1. May 9, 2014

### The thinker

If each person exists in an unchanging state in the block universe, and the flow of time is an illusion caused by the way memory functions[1] (or by something else, the details are not the point), then how exactly does this sensation of 'now' work?

Even if 'now' is a psychological illusion, that still doesn't explain why or how I am experiencing this particular now and not some other now.

For example, are there an infinite number of me's at every point in time, all experiencing their own now? Or is there one me that 'travels' though the block universe, experiencing the illusion of time?

[1] 'Relation between the psychological and thermodynamic arrows of time' (http://arxiv.org/pdf/1310.1095v1.pdf).

Last edited: May 9, 2014
2. May 9, 2014

### Staff: Mentor

There is no special "now" in the block universe. There is also not an infinite number of you's. There is one you, and you are a single 4D object.

The block universe is not a psychological theory and does not attempt to explain psychology. However, at each point along your worldtube you possess the property that you experience that point as "now", so your psychological experience is certainly compatible with the block universe (as are all other observations) interpretation.

3. May 9, 2014

### The thinker

I understand that it is not a psychological theory, but as you said "at each point along your worldtube you possess the property that you experience that point as 'now'".

What confuses me is that I somehow move from one now to the next. How is that possible if there is no time in this frame of reference?

4. May 9, 2014

### Staff: Mentor

There certainly is time in any frame of reference in the block universe. There is just no "moving" from one now to the next.

The block universe is a geometric concept. If you have a piece of paper and you draw a line on it the line has a tangent vector at each point, and that tangent vector can differ from point to point, even though the line itself is not moving. Similarly with time in the block universe.

5. May 9, 2014

### The thinker

Sorry, I meant that when looking at the 4D me, from the outside as it were, that there is no time.

I understand that each point of time can be different in the block universe, it makes perfect sense that each slice is different, and also that my brain causes the me in each time slice to feel like one direction is past and the other is future.

The part I am stuck on is how my personal awareness can move from one slice to the next.

Perhaps it is not a question that physics can answer.

6. May 9, 2014

### pervect

Staff Emeritus
Any particular particle has a 4-velocity. This is just a vector in the geometry. Hopefullly the concept of the 4-veocity is familiar, if not try "Space-time physics" by Taylor & Wheeler or some other textbooks with a 4-vector treatment.

"Now" is just a 3-surface that's orthogonal to the 4-velocity of the particle. You look for the space-like vectors that are orthogonal to the 4-velocity at some particular point, the 3-surface spanned by these vectors is "now" at that point.

If you want to consider an "observer" as a collection of particles, things get less clearcut. I'm not sure that's part of the science. I'd start by considering what the 4-velocity of the observer. If all parts of the observer didn't have the same average velocity, they would wind up spreading out, so the center-of-mass velocity seems like a good first start for the velocity of a collection.

7. May 9, 2014

### The thinker

I think you may have misunderstood the question.

I am essentially asking how one's awareness can move from one 4-vector to another. This is sort of a psychological question, but at it's root a physics question.

8. May 9, 2014

### Staff: Mentor

It doesn't. At least, not according to the block universe concept.

The block universe is just an interpretation of SR. If it doesn't help you think about relativity then just ignore it.

9. May 9, 2014

### pervect

Staff Emeritus
When you phrase it that way, I would say that your question is philosophical rather than scientific. Though if you think it's scientific, you might propose a few experiments that would help you answer it.

That's assuming that I understood this version of the question any better than the last one - the apparent difficulty in pinning down just what the question is seems to me to be an indication that the base question is probably philosophical.

10. May 9, 2014

### The thinker

Yes I suppose so!

I figured that as it involved something physical moving (unless you believe in a soul!), then there would be a natural physical answer.

11. May 9, 2014

### Fredrik

Staff Emeritus
Who says it does? A 4-vector identifies something like a single event, or the tangent to a particle's world line at that event. It doesn't describe awareness.

If we assume that classical mechanics can describe a conscious physical system, then that system's experiences would, like everything else, be described by a set of timelike curves. Perhaps you meant to ask how awareness moves along those curves. The answer would be that it doesn't. The curves are the awareness.

12. May 9, 2014

### The thinker

Ah, now this is the kind of answer I was looking for.

Quite mind boggling!

13. May 10, 2014

### georgir

It is mind boggling, but is still just pointless philosophy.
"Why am I now and not 5 seconds ago, 1 year into the future or whenever?"
"Why am I me and not you or the president of the USA, or Moses or whoever?"
Pretty much nonsense questions.
(offtopic: and the many-worlds interpretation counts on that to shut you up about why you think it is stupid...)

If a tree falls in a forest...?

14. May 10, 2014

### The thinker

I don't think it is pointless philosophy.

Consciousness is a physical process, a real phenomena.

Would using a less loaded phrase like 'black box' help?

There is a black box which the available evidence suggests exists in only one slice of the block universe at a time. How can this be explained?

I am not trying to suggest that the block universe is wrong. I love the idea. I just want to understand it. I assumed that this question had an answer.

15. May 10, 2014

### Staff: Mentor

That is true for all objects in the block universe. The statement "X exists in only one slice of the block universe at a time" is tautologically true since the "slice" you choose defines what is meant by "at a time".

I think that the problem that you are having is that you are minsunderstanding something about the block universe interpretation. You keep ascribing things to it that it doesn't say, like this idea that you move from one now to another. In the block universe you don't move from one now to another. There is no block universe explanation for it because it simply isn't true according to the block universe.

I am not sure what you are misunderstanding, but the block universe is just an interpretation, and like any interpretation, there is nothing scientific requiring you to use it. It is just a philosophical aid to understanding relativity, and if it doesn't help, then don't use it. I like it, but there is no need for you to do so also.

Last edited: May 10, 2014
16. May 10, 2014

### bahamagreen

So the black box is like a clock, has no psychology or philosophy, but it always indicates what time it is "now"...?

If the block universe interpretation is that things don't move through time, it does allow that things change value through time... the question still remains how we observe these changes with respect to an apparent "now" that increments through time.

Last edited: May 10, 2014
17. May 10, 2014

### Staff: Mentor

I am not quite sure how you think that the question remains.

At each event along an observer's worldline the observer calls that time "now" and has access to information only from within the past light cone. That is all compatible with observation, experience, and with the block universe interpretation (and any other interpretation). What incompatibility do you think remains?

18. May 10, 2014

### bahamagreen

I kind of understand your point, but it makes for a peculiar world.

The Block Universe seems like a sculpture, or like a stack of frames comprising a movie; but our experience is more like listening to a piece of music, where we always are at some point in the piece.

I think I see how time being one of the Block Universe dimensions seems to provide for a worldline of events without these events existing "at the same time", and how each event will feel like "now", and the lightcones ensure a consistent past/future causality distinction at each event, etc.

But what that does is make ALL points in the sculpture or all frames in the movie behave consistently as a "now" event.

But why do we only have the present and particular "now" moment? Of course, the Block Universe interpretation will say that this is just this one and it is consistent and completely correctly connected... as are all the others of the worldline... even though they don't "all exist at the same time" nor are there "multiple yous spread along" the worldline, nor are you "travelling" the worldline.

The anthropomorphic principle seems to maybe apply here...? Every event will be experienced as a "now", including the sense of that "now" being the unique and only present "now"... along with the other consistencies and connections that support that sense.

19. May 10, 2014

### Staff: Mentor

You've stated this wrong. What you should say is: we at the present "now" have the present "now".

In other words, when you use the phrase "the present now", you are implicitly picking out a particular point on your worldline; but that very act of picking out a particular point on your worldline also picks out a particular state of your brain, the one that has precisely the information available in the past light cone of that particular point. Each distinct point on your worldline has a different past light cone, and therefore a different set of information available to your brain, and therefore a different state of your brain.

And that is all you are really saying in what I quoted above: that your brain state is different at each different point on your worldline, and each different brain state incorporates a different "now"--more precisely, the brain state *is* what you are really referring to when you refer to your sense of "now", of "the present and particular now moment". That's all there is to it.