What is time?

[AnssiH]

Originally Posted by modest

You're not wrong, you're just inhibiting yourself. It wasn't that long ago people were honestly trying to figure out if the solar system was geocentric or not. Understand, we had a model that described the motion of the planets in the sky without the 'correct' (earth orbits around the sun) description. So there were two models and neither really worked any better than the other.

So, people I'm sure asked which was real - which was in the middle, the sun or the earth. You would have said "faeries vs. elves" and stayed above the stench. Good for you, meanwhile we did figure out which model was correct.

Same will no doubt happen with curved spacetime vs. gravitons or many other differences in interpretation we have today. Yeah, believe it or not, one of these interpretations is the more correct one.

"faeries vs. elves"

~modest

EDIT:

We've both dragged this thread off topic. I appreciate that you will want to reply to this, and you should, but we're not getting anywhere and we should respect the topic me thinks.

I would just comment quickly that from my perspective, the inhibiting factor is that many people tacitly view the elements of some specific (theirs) valid worldview as ontologically real; i.e. assume those elements exist independent of that particular valid worldview. When they do that, they loose perspective on what sorts of valid models can really be built. They may think any model that does not define "photons" or "electrons" cannot possibly be correct, or indeed, any description where simultaneity is not relative to inertial frame cannot be correct.

Likewise, in my view it is not really inhibiting to stay away from the ontological arguments and rather investigate the constraints on valid worldviews (especially as it appears there exists surprisingly specific constraints if you take into account what sorts of assumptions would be undefendable). Even when you don't take any ontological preferences, you can investigate whether geocentric or heliocentric model is valid predictionwise... ...also in this case it is interesting that geocentric model can be twisted into a valid view by changing your perspective on space and inertia and such things - i.e. one could see the situation as geocentrism by changing completely what it means to "go around something". That of course would amount to much more complicated worldview than the heliocentric one.

That is to say, someone who did not take any ontological preferences, could have compared the heliocentric & geocentric models, and said over the heated debates; "it is much simpler to explain our night sky by the definitions of the heliocentric model, plus its definitions of space are simpler than what the geocentric model requires. You probably want to use heliocentrism in your descriptions of the situation".

That is in fact completely in line to Kuhn's description of scientific revolutions. E.g. some new observation (planets moving backwards for brief moments in our sky) makes the description of the situation more complicated when you describe it in terms of an old model (if you believed in geocentric models, you saw that observation as figure-8 orbits or perhaps as even more complicated motion). But someone realized that by changing some definitions/assumptions, the description of the situation suddenly became much simpler -> heliocentrism.
(That someone is often from a new generation of scientists; someone whose mind was not yet too entangled together with the existing models)

It is quite likely that our current scientic models have got some overly complicated ways to describe some situations. Dark matter comes to mind. It is not trivial to make new definitions that yield simpler overall model, but to my knowledge all the attempts to redefine space/gravity to explain away dark matter have been met with fair bit of resistance for no objective reason at all. Dark matter itself is often presumed to be ontologically real element, existing independent of our definitions in our worldviews.

Oops that wasn't quite as quick comment as I hoped for... Well I suspect this was useful or interesting commentary for some people anyway... I won't drag this thread off the subject more.

-Anssi

[Overdog]

I just googled Time, and discovered that my wife's seemingly (to me) brilliant view of it was developed by Gottfried Leibniz and Immanuel Kant a long "time" ago. I should have known that.

Sorry for wasting everyone's "time" with that post.

Hmmm...Can the universe waste time?

It seems we can conjecture and theorize about time until it runs out. Ah well, it seems this thread is timeless.

[AnssiH]

Originally Posted by modest

I might get some resistance by putting this in the language of physics, but I think it's best described with a lightcone:



described on wikipedia where the "hypersurface of the present" is outside our past light cone and therefore we do not experience it - we have no direct knowledge of it. I think this implies quite a bit about the workings of time and space. In particular, how our experience is limited to events not spatially separated from us. The further an event is spatially distant from us, the further in the past that event must be.

Since you pasted that picture, I should comment that when I was referring to the "ontology of the simultaneity planes", I was talking about what is dubbed "hypersurface of the present" in that picture. With the definitions of relativity, the visualized surface is for an observer who is not moving in that picture. If the red dot was moving in that pictured frame, his "surface of the present" would be tilted. Depending on the observer's speed, it could be tilted in any angle as long as it did not penetrate the light cones.

That means, if the observer was changing directions, its "surface of the present" would be said to tilt back and forth in such manner that some events would move through the present "backwards"; i.e. some things around the observer would move backwards in time (of course beyond the sight of the observer).

I.e, if you take relative simultaneity as ontologically real, you also assume that things around you in your "present moment" can move backwards in time if you change directions, but you just can't see it.

Of course at this point I should remind you that it is possible to build a valid view of reality where such simultaneity planes are not ontologically real. I think that is just one particularly interesting aspect of modern definitions on "time".

-Anssi

[Overdog]

Ok all, it's been fun, but I'm beginning to percieve that no matter what time is, this thread is a black hole that is sucking vast quantities of it right out the fabric of my reality. Since I have only a limited supply of it, I'm going to have to leave orbit, now....

[ldsoftwaresteve]

I have really enjoyed this discussion. I have seen beautifully elegant descriptions from many different points of view and witnessed folks expanding their world to include a little doubt, which I think is very healthy. We're strong enough to move forward with our eyes completely open.

And I think I finally understand, at least in part, what DD has been talking about thanks to Ansii's repetition of constraints on worldviews. I may not be smart enough to abstract out those constraints and deal with them as building blocks, but at least I am able to see that if there are patterns in the constraints or relationships between them something pretty important might be identified.

Just one more thing and I'm done. I wish we had some tools to go back over this thread and somehow tie things together with other threads. I guess I'm talking about a manual abstraction process where we can 'back out' and look for patterns in arguments, etc.

In other words, threads could be of two basic types: initial discussions covering a wide set of views - and mature threads, meaning, the thread has been analyzed and integrated into other structures. I'm not smart enough to do that so somebody else can think about it, ok?

I have to go now for a while. We just bought a house and are moving. So much to do and so little time to do it.

[modest]

Originally Posted by AnssiH

Since you pasted that picture, I should comment that when I was referring to the "ontology of the simultaneity planes", I was talking about what is dubbed "hypersurface of the present" in that picture. With the definitions of relativity, the visualized surface is for an observer who is not moving in that picture. If the red dot was moving in that pictured frame, his "surface of the present" would be tilted. Depending on the observer's speed, it could be tilted in any angle as long as it did not penetrate the light cones.

That means, if the observer was changing directions, its "surface of the present" would be said to tilt back and forth in such manner that some events would move through the present "backwards"; i.e. some things around the observer would move backwards in time (of course beyond the sight of the observer).

I.e, if you take relative simultaneity as ontologically real, you also assume that things around you in your "present moment" can move backwards in time if you change directions, but you just can't see it.

Of course at this point I should remind you that it is possible to build a valid view of reality where such simultaneity planes are not ontologically real. I think that is just one particularly interesting aspect of modern definitions on "time".

-Anssi

I'm glad you clarified that because I had no idea that's what you meant. It's described a bit on wiki's world line:

Originally Posted by Wiki

The present instant is defined for a given observer by a plane normal to her/his world line. It is the locus of simultaneous events, and is really three-dimensional, though it would be a plane in the diagram because we had to throw away one dimension to make an intelligible picture. Although the light cones are the same for all observers, different observers, with differing velocities but coincident at an event or point in the spacetime, have world lines that cross each other at an angle determined by their relative velocities, and thus the present instant is different for them. The fact that simultaneity depends on relative velocity caused problems for many scientists and laymen trying to accept relativity in the early days. The illustration with the light cones may make it appear that they cannot be at 45 degrees to two lines that intersect, but it is true and can be demonstrated with the Lorentz transformation. The geometry is Minkowskian, not Euclidean.

And your particular objection is called the andromeda paradox:

Rietdijk-Putnam argument - Wikipedia, the free encyclopedia

which is only a paradox (like so many things in SR) if you assume a person can receive information faster than light or assume people can know things which are impossible to know. In other words, only by making bad assumptions is the relative plane of simultaneity a problem rather than always perfectly consistent with observation.

~modest

[Doctordick]

Originally Posted by modest

...which is only a paradox (like so many things in SR) if you assume a person can receive information faster than light or assume people can know things which are impossible to know. In other words, only by making bad assumptions is the relative plane of simultaneity a problem rather than always perfectly consistent with observation.

But, my point is that Einstein's picture “is making those bad assumptions” by his definition of time; and it does indeed lead to some subtle problems. Consider a world where clocks accurate enough to be used as “the definition of time” were small enough to wear as wrist watches by everyone. Then everyone would know exactly what time it was (by definition) and no two people would agree as to what time it is. Add to that the fact that things can only physically interact when they exist at the same time and “time” seems to have failed in its purpose. That is why I say “time is not a measurable variable” and it only has meaning along the evolving path of an entity. It is a useful parameter for describing the phenomena impacting the evolution of that entity and any additional properties can not be defended.

My definition of time stands! The past is "what we know" and the future is "what we do not know". The present then becomes the boundry (of our knowledge). The fact that we find it convenient to think of what we know (the past) as a collection of "presents" for the purpose of ordering our world view (and the evolution of specific phenomena) does not make time a measureable variable. That is an unjustifieable leap of faith enjendered by the success of Newtonian mechanics. He introduced the idea that the future could be known if the past were known and Einstein's picture is soundly based upon that erroneous illusion. That is precisely the source of the problems between general relativity and quantum mechanics.

Have fun -- Dick

[AnssiH]

Originally Posted by modest

And your particular objection is called the andromeda paradox:

Didn't mean to object the validity of relativity at all, if that's the implication you got.

btw, rather interesting that the "Rietdijk-Putnam-Penrose argument" refers to something that surfaced as late as in the sixties. That implication regarding "present moment" should be abundantly obvious immediately from the premise of relativity. I'm sure many people have made comments about it, including Einstein.

Rietdijk-Putnam argument - Wikipedia, the free encyclopedia

which is only a paradox (like so many things in SR) if you assume a person can receive information faster than light or assume people can know things which are impossible to know. In other words, only by making bad assumptions is the relative plane of simultaneity a problem rather than always perfectly consistent with observation.

Yes, in other words the simultaneity planes themselves are not observable at all; they are things we have defined as part of relativistic spacetime, but their ontological reality is an assumption.

Following that, when people think about the implications of relative simultaneity, many end up assuming there is then no specific "present moment" existing at all; that it's not fair to say whether Andromedian invaders are underway or not, but rather future and past exists "all the time". That obviously leads to rather specific assumptions to explain our subjective experience, where things still seem to be "moving".

Well, if that's now clarified, one should pay attention to the possibility of modeling reality with absolute simultaneity, or technically with just about any sort of simultaneity. By defining simultaneity as it's defined in relativity, it makes certain aspects of our description of nature very simple. Yet, it being valid does not constraint the reality itself into a static spacetime block in any ontological sense. It is poor judgment when people think relativity = static spacetime.

That is not to condone the ontology of absolute simultaneity as much as it is to point out that spacetime is also part and parcel of our conception of reality; A matter of defining (many) things that way. Referring to DD's analysis, it is rather interesting that it seems it is the symmetries in our "definitions of entities" that make relativistic descriptions valid.

Ps. Note that the Wikipedia page listed as one of the references "A Rigorous Proof of Determinism Derived from the Special Theory of Relativity".Well, that is simply not valid. Someone is seeing that as "proof" because they take some assumptions in their worldview as ontologically valid, on pure faith.

-Anssi

[modest]

Originally Posted by Doctordick

But, my point is that Einstein's picture “is making those bad assumptions” by his definition of time; and it does indeed lead to some subtle problems.

I think Einstein's definition leads to problems with your world view. His definition has never led to problems of agreement with observation.

Originally Posted by Doctordick

Consider a world where clocks accurate enough to be used as “the definition of time” were small enough to wear as wrist watches by everyone. Then everyone would know exactly what time it was (by definition) and no two people would agree as to what time it is.

Time is relative. What's the problem here?

Originally Posted by Doctordick

Add to that the fact that things can only physically interact when they exist at the same time and “time” seems to have failed in its purpose.

You want Einstein's definition of time to fail in its purpose which would then support your personal philosophy of anti-realism. However, such a thing cannot be managed. Relativity is one of the most successful theories of all time. It has yet to disagree with observation. The only way to attack such a theory is to make a better one that makes better predictions with better theoretical structure. Your sentence above doesn't accomplish that.

Originally Posted by Doctordick

That is why I say “time is not a measurable variable” and it only has meaning along the evolving path of an entity. It is a useful parameter for describing the phenomena impacting the evolution of that entity and any additional properties can not be defended.

By this reasoning length is not a measurable variable. The front and back of a train have spacetime separation and therefore a train has no length. That's not useful.

Originally Posted by Doctordick

My definition of time stands! The past is "what we know" and the future is "what we do not know". The present then becomes the boundry (of our knowledge).

This is not a definition of time. I appreciate that it has meaningful constraints that are related to time. But, taken literally "the future is "what we do not know"" means anything we do not know is in our future. This is untrue because what we "know" is not an exact way of describing our past lightcone.

Perhaps you meant to say "we can only know things from our past".

Originally Posted by Doctordick

The fact that we find it convenient to think of what we know (the past) as a collection of "presents" for the purpose of ordering our world view (and the evolution of specific phenomena) does not make time a measureable variable.

Yet there is something (some concept) that distinguishes two past events that are exactly the same in every way except for 'time' that separates them. Your definition makes no allowance for that. It is therefore incomplete at best.

Originally Posted by Doctordick

That is an unjustifieable leap of faith enjendered by the success of Newtonian mechanics. He introduced the idea that the future could be known if the past were known and Einstein's picture is soundly based upon that erroneous illusion. That is precisely the source of the problems between general relativity and quantum mechanics.

Have fun -- Dick

I agree that the usefulness of the concept (and the normal definition) keeps it alive and kicking.

~modest

[modest]

Originally Posted by AnssiH

Yes, in other words the simultaneity planes themselves are not observable at all; they are things we have defined as part of relativistic spacetime, but their ontological reality is an assumption.

I think you're the only one assuming it has any ontological reality. I honestly don't think that would be a normal assumption. The present instant is no more real than a world line.

~modest