Science Forums 2

[AnssiH]

Originally Posted by ldsoftwaresteve

Here's my definition of 'identity': a re-cognized pattern. Existence doesn't have cognition so there isn't anything behind the concept of identity except when you come at it from the point of view of a conscious entitiy.

Or from the point of view of a model of reality.
"Identity" can be defined as an assumption of something being the "same" from one moment to the next (or "through time"). In an ordinary worldview something like a shadow or a rainbow is taken to not preserve its identity ontologically, but we assume some things do. What things, that depends on how did we model that "unknown data". Should serve you well to not take any identity on anything for granted.

On the other hand, there are long duration structures that we could assume have been around 'forever' unchanged through the continuum of nows. That hints at 'stable' as opposed to unstable and implies a fundamental building block.

We certainly tend to think there must be some fundamental building blocks out there, but even then we don't know if we have that tendency only because our comprehension of everything works that way, i.e. it is *our* feature to handle everything that way, not reality's.

Another point is that even if there are fundamental building blocks, it is always possible to create a plethora of valid "mental models" on top of them (to explain their behaviour). That means no experiment can make a separation between different models.

And it's impossible to consider that without using the idea of time to do it. So, 'time' becomes part of a reference that we use to create identity. It's a way of tagging patterns that enables us to detect change.

Well that sounds quite close to how it is in Doctordick's analysis. It's kind of a minimum definition, a reference to changes in our knowledge.

I'm cutting you out here because it seemed to me the rest was getting out of the topic a bit

I'll just comment that the main purpose of the whole "object definition" exercise has been to point out how our perception/conception of reality has quite a bit to do with our own subjective definitions rather than being just us probing objective reality directly. Whatever probing we do, we understand it based on a model we built out of our very own assumptions/definitions.

Originally Posted by modest

comparing Sally's T which we call to Tommy's T. This tells us that Sally ages faster than Tommy. This is not an effect of observation. This is something that ontologically happens. Sally may age 10 years on this carousel while Tommy only ages one month.

My idea of time would be the concept that needs to be added to the above situation to fully describe what's happening. It's written as T and we call it time. However, you are claiming that there are multiple self-consistent ontologies of time that describe T here. I wonder if you can give a couple examples.

Yes, though note that I've been using the word "ontologically" differently than you do. I use it differently in the next sentence as well; The underlying "ontological" reality behind "time dilation" can be seen in many different ways, though all different views can agree it is predictionwise quite valid to describe the situation as "Tommy ages more slowly".

E.g. are Sally and Tommy passing through "time dimension" of "relativistic spacetime" in real ontological sense, or is spacetime just mental construction and the actual ontology is perhaps closer to, say, all natural processes in Tommy's situation are moving more slowly than in Sally's (rather like clock slowing down under stress)

...or is the root of relativistic time description found from our methods of defining entities in unknown data. To investigate that route, you might want to take a look at that epistemological analysis.

I was bringing up relativity of simultaneity instead of time dilation directly because that offers a fairly simple route to considering what ontological implications relativity makes on time and associated components;

Originally Posted by Overdog

I have to agree with this...lead on.

In a pre-relativistic view we'd be quite inclined to believe that the reality around us is in some definite "now" state even when we are not yet observing that state.

In a relativistic view we'd be inclined to believe it doesn't. Because the notion of simultaneity (~now moment) is defined as relative to your direction of motion. In a naive sense you could imagine that clocks in alpha centauri move backwards when you are accelerating away hard enough (they'd do so beyond your sight of course).

For anyone who is not familiar with the notion of relativistic simultaneity, here's a thought experiment pasted & edited from my old post;


We are on earth, and there is a spaceship near Alpha Centauri, approaching us at steady speed. Assuming the light is approaching us at speed C, we can figure out what is the "real" moment when the spaceship is just passing Alpha Centauri. On earth, we put up a signal beacon at that moment.

SR says the moment "we put up the beacon" and the moment "the spaceship passes Alpha Centauri" are not really simultaneous in any inertial frame but in ours. I.e. when the spaceship receives a signal from our beacon, it can figure out when did the beacon go up, and assuming the speed of light to be C in its own inertial frame, it will conclude that the beacon went up much much earlier than when it was passing Alpha Centauri.

This means that when the spaceship had not yet even passed Alpha Centauri in your frame, in its own frame you had already put up the beacon long time ago; your future had already happened I.e. your future actions have "already happened" from the point of view of many inertial frames.

It also means that if the spaceship now accelerates ("brakes") to the same direction of motion where you are, it will come to share the simultaneity with you. For example, if in its original frame you had put up the beacon three weeks before it reached Alpha Centauri, then when it brakes, the clocks and everything on earth "rewind" back to the state where they were three weeks ago; to the moment when you were just putting up the beacon.


Of course the above doesn't really make sense as is, it's a consequence of certain way of understanding the "now" (which we got from certain way of modeling the timewise evolution of things). But if you follow the implications of such a notion of simultaneity, you can see why some people have made the assumption that reality is ontologically a static spacetime block where future and past exists all the time, and nothing moves except in some dualistic sense our "consciousness" (that assumption of "consciousness" is also just a consequence of trying to fit in our subjective experience coherently together with relativistic description of reality where time is a static dimension and nothing moves... ...which of course makes it immediately incoherent or at least very unelegant to suppose "consciousness" nevertheless moves over and beyond the control of "time", which was supposed to be the source of all motion!)

Also you should note that "length contraction" is a direct consequence of defining simultaneity as relative. That is simply because the geometry of an object must be defined as "where its extents are found at a single moment". Re-define what "single moment" means, you also redefine the geometry of that object.

Aaaand what follows is that if you take length contraction as ontologically real, you also take those simultaneity planes as ontologically real, and consequently you take clocks that move backwards in time as ontologically real... ...and that eventually forces you to take rather specific ontological view on time (as a static dimension), and creates rather specific constraints on your ontological view of your own subjective experience.

Anyhow, I should point out, if it wasn't obvious all along, that relativity doesn't allow for direct observation of any "simultaneity planes". It would never be possible to actually see clocks moving backwards or anything like that. We can measure some objects moving at different rates in different situation, but to explain that it is not necessary to suppose all of past and all of future exists all the time.

It is quite possible to arrive to the same observable predictions even if you define simultaneity as absolute, as long as you define other things in your worldview appropriately as well. (A simple way to see that this is indeed possible is to imagine a static spacetime block and just choose any arbitrary simultaneity plane as "absolute"... ...nothing inside that spacetime block is affected, just the way you describe things becomes very complicated if this is the only change you make on your worldview)

I am aware of few other ontological takes on relativity of simultaneity (or on "reality of the now-moment"), some more coherent than the others. I have no idea how many people here take see static spacetime as ontologically real. The actual reason I am bringing all this up is not to argue the ontological validity of one or the other view, but just to once again point out how these things have everything to do with how we define things in our personal model of reality. Just an attempt to open up your minds to see how one assumption constraints other assumptions and vice versa. (That's why I said "let's see if you can analyze your thoughts objectively"

Modest, in case you are wondering, that has got very little to do with the math of relativity. It just has to do with what kind of reality that math implies (or what sorts of realitites are still possible behind that math, many of which are not very evident from the math directly)

-Anssi