Does time exist?

Well if you think about it,

Do things happen because time passes

Or does time pass because things happen?

Imagine, say nothing in the world was changing. Everything was still. No movement, no forces, no anything. Consider one moment. Now consider a minute on from that. Then an hour. A day. A month. A year. It's still the same. Nothing has changed. How do we know how long has passed if we have nothing to gauge it by?

But now the inverse. Say we imagine time isn't passing, but things change. If something started of at point A, then moved to point B, while time isn't changing, did it start at A? or at B? or at some point inbetween A and B. If everything happens simultaneously, then how do you know where it started/finished?

My thoughts on the subject.

roosh wrote: »

Are you referring to "the block universe" interpretation there, where spacetime is 4D, and we only experience our "now slice" of the block universe.

Yup.

A number of questions arise from that; if we take the example of your 8yr old self having his/her birthday party, the natural question would be, how did your 8yr old self not age as you aged? You were that 8yr old, and you grew to be whatever age you are now; how did the 8yr old you not age along with you; how can he/she still be having their 8th birthday party?

I think you're mistakenly taking the younger and older self to be different, especially when you say the 8yr old should age along with you. Both would be connected as a unity through time. The 8yr old at the 3rd of April is the same as the 8yr old on the 9th of April. The 8yr old on the 3rd of April is always that age, ie. no one ever ages in any real sense of the word, they simply experience the individual moments along the static timeline of their existence.

They are still having their birthday party, but by they it's just you. Your past self is statically frozen as an extended temporal birthday party. In fact the you that is going to reply to this has already done so, it's just that your awareness of that moment has not caught up to it yet. In effect you are always moving into your future self.

I think however, that this doesn't really solve or elucidate the nature of time at all. All that has happened is that there is now something else we have to explain, namely, how the 'now' point moves along the frozen 4-Dimensional time space. Everything exists already, but they don't all exist as 'nows', so why not?

I think you're right on the empirical comment, however I think the notion of 4-Dimnesional time has arisen rather as an attempt to overcome some of the conceptual problems of regular time. (Don't ask me what those are )

The answer to that conundrum, I think, appears to be that we, somehow, exist as geometrical "world lines" already plotted out in absolute spacetime. This further gives rise to the question, if we are geometrical world lines, with an absolute existence in spacetime, and not necessarily moving - but moving through time?? - then how is there the illusion of relative motion between observers and objects? How do these non-moving worldlines experience relative motion?

I'm not too familiar with relative motion to be honest. Will I even hazard a guess... Maybe if we could furnish a simple example of it for myself. Oh yeah, so the basic example of the twin who travels around the earth a near light speed and returns to his more aged twin.

Would it be possible to explain this in the sense that the progression through time, the consecutive 'nows' for each observer are not progressing at the same speed? You don't need different time lines because the 4-D timeworm is essentially 3-D extended through time, it's not just a line, which is 1-D. The person at near light speed is travelling through the static time faster than the other people. I think you just need to say that there are different 'now' points in 4-D time.

Sorry for my poor explaining!

I think the world line is slightly different from philosophical 4-Dimensionalism.

For 4-Dimensionalism objects aren't travelling through 4D spacetime, they are fixed at all points. Their past and future states already and always exist.

I think the world lines are a measure of movement through spacetime and is not saying that the past states still exist. Would I be right in saying that?

For 4Dism sapcetime is the temporal and material extension of objects, it's not something through which they pass.

roosh wrote: »

Does the world line not represent the object in spacetime; that is, the object is fixed at all points and would be represented by a line?

I'm not sure what the status of the world line is. If it's just representing the movement of the object through time it's not necessarily saying it still exists at those points, whereas 4Dism is saying that. Morbert is probably in a better position to clarify the world line idea.

It appears to be a pretty big assumption, though, that past and future states already and always exist; I think it stands in the realm of the unverifiable.

Probably. But as philosophy it's often just looking for the necessary conditions of time, e.g. things must always already exist in past, present and future.

Not that I agree. It just is what it is.

roosh wrote: »

Why would you say they are the necessary conditions of time?

I think one of the problems that 4Dism tried to solve was reference to past events. So I talk about yesterdays dinner, I must be refering to something for the words to mean anything. Otherwise I'm refering to nothing and it loses meaning. So the 4Ders go as far as to state that the objects (necessarily) always exist, otherwise our talking about them wouldn't make any sense.

I haven't kept up with the debate on this issue, so it may actually be rather dated!

I would say that things used to exist, but existed in the present, which subsequently changed. They don't exist in the future, nor will they ever; they only ever exist in the present.

That would make you a Presentist

Edit: It certainly looks like 4Dism and world lines may be the same thing according to that wiki page. "This theory depends upon the idea of time as an extended thing and has been confirmed by experiment, thus giving rise to a philosophical viewpoint known as four dimensionalism."

roosh wrote: »

Have Quantum Mechanics and Einsteinian relativity been fully reconciled, and does such a reconciliation lead to something termed "the problem of time", where both theories appear to use different conceptualistions of time?

Quantum mechanics and special relativity have been fully reconciled. The postulate that space and time are on equal footing, and part of a larger relation called spaceime has produced some of the most accurate predictions in physics.

Quantum mechanics and General relativity have not been fully reconciled because of the dynamics of the gravitational field. One approach has been to canonically quantize the Hamiltonian in the context of a uniquely foliated space-time. I.e. Slice spacetime into 3D spaces, parametrised by a parameter, and build quantum mechanics in this context. This does not result in presentism, however. The gauge parameter, used to construct quantum mechanics and the presentist "time label", are not equivalent. All you can say about these particular slices is they make the maths easier.

roosh wrote: »

and how do static worldlines give rise to the perception of relative motion?

Relative motion manifests as a difference in the shape of two world lines. If we consider the simple case of a globally flat spacetime (I.e. No gravitational pull), two objects at rest with respect to each other will have parallel world lines.

roosh wrote: »

This explains how we would graph the two worldlines of two different objects; that is, it explains what shape two worldlines would have; it doesn't explain how two static worldlines, at angles to each other, give rise to the perception of relative motion.

EDIT: I think you're putting the cart before the horse in the above formalism; I don't think it is accurate to say that relative motion manifests as a difference in the shapes of two worldlines, because the shape of the worldlines isn't what manifests in the physical world, it's the relative motion that manifests. So it would be more correct, I think, to say that the difference in shape of two worldlines manifests as relative motion - the question remains as to how this happens.

Your conflating terms again. By manifest, I mean that is how the observation of relative motion manifests in the spacetime structure of events.

Also, what about "the Problem of time" in Quantum Gravity and Cosmology that prompted Lee Smolin to teach this series of lectures - regardless of his own personal opinion on the matter.

Also, what about the Wheeler-Dewitt equation which appears to suggest a timeless universe?

And as I explained before, the timeless universe they are talking about is not the presentist universe you are talking about.


Go to 18:19

"Not only is all of the past and all of the future present, but all possibilities of the past and future."

The difference is, in vanilla relativity we have events within a 4D spacetime. In the "non-time" model, we have a space of all possible configurations of the universe.

roosh wrote: »

It isn't me that is conflating terms, but you may just have misunderstood the question. The question was, how does the spacetime structure of events manifest as relative motion i.e. how do static worldlines, ultimately at rest relative to each other manifest as relative motion?

And I said it is the shape of the world lines that exhibit the relative motion we associate with observers and objects. If you're asking why we don't atemporally perceive the entire world line of ourselves, that boils down to the question of how perception manifests from things, an open question.

I wasn't referring to Barbour's theory, although I wonder does his theory incorporate the idea of a universally shared present moment?

I was specifically referring to "the problem of time", as per the lecutre seires given by Lee Smolin, and also the Wheeler-DeWitt equation:
What if time really exists?

They are the same theory: "The Wheeler-DeWitt equation embodies a stark form of presentism: it simply tells us which states the universe can find itself in, and says nothing about any evolution through time. " Is equivalent to Julian Barbour's:"The quantum universe is likely to be static. Motion and the apparent passage of time may be nothing but very well founded illusions." I.e. They are saying the universe is an unchanging configuration space, and change is an illusion generated by the Hamiltonian. The "present" in this case, is not a single 3D hypersurface, but rather all possible hypersurfaces, and all possible configurations.

I am assuming the world line issue has been resolved.

Presentism is the idea that only the present moment exists; so regardless of the configuration of hypersurfaces, the Wheeler-DeWitt equation embodies a stark form of the idea that only the present moment exists.

No it doesn't. This is what I have been saying. It gives us all states the universe can be in. It says nothing about the evolution or "change" of the universe. The quote you used even says this:

"The Wheeler-DeWitt equation embodies a stark form of presentism: it simply tells us which states the universe can find itself in, and says nothing about any evolution through time."

I.e. The Hamiltonian is simply a constraint. It does not generate change. The "stark form of presentism" is presumably an allusion to the fact that a static universe exists.

I'm not entirely sure about the idea of a 3D hypersurface, but, if I understand correctly, I don't have too much trouble with the idea that the universe is an unchanging configuration space and that change is an illusion.

Still, it would represent presentism though.

EDIT: it is probably worth clarifying the point about change being an illusion; change still manifests in the physical world we experience, but the physical world we experience is illusory.

You understand that the configurations corresponding to your past and your future (and all possibilities of your past and future, permitted by the Wheeler DeWitt equation) are part of this unchanging configuration space, right?

roosh wrote: »

Our system can exist as a single quantum state, where past and future exist eternally, all within the parameter of a single, universal present moment; because what constituted the past state of the system continues to exist, but has changed its form to that of the present; and the present will change to a state which we now call "the future", but what constitutes that "future" state exists in the present moment, just in a different form.

That is not what a configuration state is. What you are saying is "The ball was here, now it's there, but the ball always exists". A timeless, static universe says "The ball is here" and "The ball is there" both exist. They are both different "configurations" that exist in an all-encompassing space of configurations. Ontologically speaking, it gets rather messy because a quantum state is not just a configuration, but rather a function over all configurations called a "wave function". But what is important is that, in the traditional, non-relativistic, Schrodinger formalism of quantum mechanics, the universe is a single quantum state that changes. That change is described by a mathematical object called the Hamiltonian operator. This is the presentism you are talking about. Time is just a parameter of change, and all that exists is the single quantum state. In quantum cosmology, the Hamiltonian no longer describes change. Instead, it is a constraint on all configurations. Change disappears as well. All states (that are allowed) exist.

roosh wrote: »

To try and be more precise about what I am saying; I am saying that the nature of reality manifested, on the macro level, as "the ball was there"; this manifestation changed to "the ball is here". There is no evidence to suggest that the manifestation of "the ball there" continues to exist, and there is no evidence to suggest that the manifestation, "the ball is already over there" (the future), already exists.

To speak about a "ball" at the quantum level is, I'm sure you'll agree, pretty imprecise. I would be more inclined to say that, the nature of reality, which manifested as "the ball was there" continues to exist - in whatever form it does - and the nature of reality, which will give rise to the "future" manifestation of "the ball is over there, exists now.

Where the nature of reality is monistic in nature, and could be potentially be classified as a "wave function".

This is where we get back to relativity of simultaneity. There is evidence that the notion of a single "true" present does not exist, unless we assume there are unknown mysterious dynamics at work (which we also have no evidence for).

roosh wrote: »

And this is where we get back to the question of how a clock measures physical time.


The evidence that the notion of a single "true" present does not exist is reliant on the assumption that a clock measures physical time; that there is no empirical observation of "past" and "future" points to an underlying assumption of their eternal existence.


Ultimately I think it might come back to a question on the constancy of the one-way speed of light, which is an untestable assumption in relativity i.e. the conclusion has to be assumed.

The "mysterious dynamics at work" seems to pertain to experiments on the constancy of the speed of light primarily, given that time dilation and length contraction aren't actually observed in muon experiments.

I'm just wondering, if light in a vacuum had an absolute wave length, would this account for any lack of a fringe shift, or more accurately, a negligible fringe shift, in interferometery experiments?

That question might be better suited to the physics section though.

The mysterious dynamics pertain to explanations of the constancy of the two-way speed of light. It is not only an untestable assumption, but a large collection of unparsimonious, untestable assumptions that happen to produce Einstein's relativity. Even at my most generous, I will say that, at the very least, the notion of relativity you adopt has no fewer assumptions than the spacetime notion of relativity.

roosh wrote: »

Genuinely asking; did you mean to type the emboldened bit; or am I just picking it up wrong? Did you mean to say Lorentz's relativity; because it sounds like you are saying that Einsteins relativity is based on a large collection of untestable assumptions - I'll just put it down to a freudian slip

The thing is, I think that Lorentzian relativity can be stripped of certain assumptions; I don't think it requires the assumption that an absolute reference frame exists, it simply has to allow for that possibility; which is not an assumption at all, and not contradicted by any evidence.

Of course, it can assume that an absolute reference frame doesn't actually exist, that all objects are absolutely in motion; not with respect to an absolute reference frame, but in the sense of absolute motion we've been discussing. A further assumption about the existence of time can be dropped, which would tally with the idea that an absolute frame of reference doesn't necessarily exist, and hence no "universal time".

I also suspect that defining a rest frame for units of measurement would also help to remove other assumptions.

I mean the untestable postulate of Lorentz's relativity, that there is an "absolute" rest, requires a wide range of untestable assumptions about the dynamics of things to be able to reproduce the predictions of Einstein's relativity.

It just strikes me that the assumptions of the spacetime notion of relativity are fundamentally untestable, and circular in nature.

As are assumptions of the Lorentzian notion of relativity.

C14 in the moon and in earth. Check levels later.... Time is relative.

roosh wrote: »

I don't think Lorentzian relativity requires an absolute rest frame to actually exist though; it simply has to allow for the possibility that one could exist, something that is more compatible with the experimental evidence than the assumption that absolute rest cannot exist.

Of course, if you suggest that Einsteinian relativity allows for the possibility that absolute rest could exist, then we can use this possibility to see what deductions we can make. One such deduction is the subject of the thread in the phyiscs forum.

It also seems however, that Einsteinian relativity requires its own untestable assumptions, which amount to circular reasoning.

Lorentzian relativity posits an absolute rest insofar as it posits that time dilation and length contraction are dynamical effects, and someone who is not undergoing length contraction or time dilation is "at absolute rest".

OK, so you would agree that Einsteinian relativity is based on untestable assumptions and circular reasoning?

Circular reasoning: No.

Untestable assumptions: Only insofar as the kinematics of relativity don't falsify some underlying dynamical explanation. I.e. It is an untestable assumption that these dynamical explanations don't exist, just as it is an untestable assumption that they do exist, or that an invisible teapot orbits Pluto.