VikingF

I think I got the point. It is easy to draw a straight line (e.g. the x-axis of a specific frame of reference) if you have a flat surface (and SR talks about flat spacetime), however, GR talks about a curved spacetime, hence you cannot describe a straight x-axis in the same way due to the curvation of spacetime. So simultaneity (e.g. the x-axis of a specific frame of reference) is relative in SR but not clearly described in GR. Is this correct?

Do I understand it correctly by saying that from Newtonian physics to SR, simultaneity went from being absolute to relative, and from SR to GR, it more or less "disappeared" (since it can only be discussed locally as you say)? Please correct me if I am wrong. I try to wrap my head around this.

Of course, but I meant the difference between being somewhere in spacetime, and at this specific point of time in spacetime. Shakespeare exists in spacetime, but not at this very point of time. According to Presentism, he doesn't exist at all, because they do not believe in a four-dimensional spacetime, hence for something to exist, it has to exist now.

You have to choose your definitions first. If to exist is to exist in spacetime, then he exists.

I think this boils down to how we define the word "exist". If by "exist" we mean "simultaneous in my reference frame" (existing right now for me), then surely, Shakespeare does not exist. However, if by "exist" we mean "simultaneous in any reference frame" (existing in spacetime), then he does indeed exist, since simultaneity is relative based on which reference frame you are in. Shakespeare is certainly existing in the spacetime, whether or not he is existing "right now" in my frame of reference. The main difference between Presentism and Eternalism is really about whether time is an own dimension or not. Presentism says "no, time is just a measurement of changes in space", while Eternalism says "yes, time is a temporal dimension containing all events that have happened, are happening, and will happen, and "now" is not a privileged point of time".

I cannot speak on behalf of all Eternalists, but I would answer it in the same way as I did in my last post: "Because that is how consciousness works". The consciousness is a process that exist from about your birth to your death. Every temporal part of you, i.e. the consciousness within your brain, remember its past and have expectations about its future, and this - somehow - creates the illusion that time is "rolling on" in the future direction. Entropy and the arrow of time could be the reason why we feel time is running in that specific direction. I don't know... I am just throwing out some ideas to think about here.

I don't see the difference. The block universe/Eternalism is the view that everything is four-dimensional, i.e. consisting of three spatial dimensions and one temporal dimension. Your view sounds like Eternalism.

1. According to Eternalism, everything exist in (and consist of) four dimensions, i.e. three spatial dimensions and one temporal dimension. An object, e.g. a person, is a four-dimensional "tube" between the its beginning and its ending moment, and a temporal part would be the four-dimensional part of the "tube"/object between two moments. 2. Eternalism is just the view that the world consists of four dimensions, i.e. three spatial and one temporal, and nothing more. We probably experience one-by-one moment because that is just how the consciousness works.

You're welcome. This topic has fascinated me for quite some years now. The main argument for Presentism that I have seen is that Relativity of Simultaneity is a part of SR that has not been tested directly, and could just be a "theoretical truth", but not a part of the ontological reality. However, it is a central part of SR and can be seen by examining a simple Minkowski diagram (spacetime diagram), and from the same diagram we can extract e.g. the Lorentz transformations, which have actually been tested and verified.

Relativity of Simultaneity. I think this is an interesting paper: http://philsci-archive.pitt.edu/2408/1/Petkov-BlockUniverse.pdf by Vesselin Petkov, who I also mentioned in a previous post.

I don't understand your ontology of time. Either only the present exists (Presentism), the complete spacetime exists (Eternalism), or the past and present exist but not the future (Growing block view). I think the growing block view is somewhat unappealing, because if all temporal parts of me up until now exist, then how can I know that THIS exact moment, i.e. what I call "now", is "the present moment", and not one of the points of time in the future of now? The temporal part of me that exists in e.g. 2001 will also say that he is in "the present" and that it is only his temporal part and his past temporal parts that exist. Hence, I think Presentism and Eternalism are the views that are easiest to cope with, and as you say yourself, Presentism is incompatible with SR, or more specifically RoS.

Yes, that temporal part of you does (did). Since you did experience it (unless you were unconscious at that moment), and spacetime is static (according to Eternalism, that is), then you did (does). At least that is how I think about it. Other people may disagree.

I think your thoughts are heading in the right direction, however, I don't think "eternal return" is the correct term to use, because you don't come back so to say. I think it is more correct to call it "atemporal existence", i.e. when you die you "still" exist - in the past, between your birth and death, and each 3D slice of you will "still" remember what is in it's past and have expectations about it's future. (And yes, "still" was not a correct term either, just to highlight that before I get a philosopher of language on my neck. )

I recommend "Relativity and the Nature of Spacetime". You can find it on Amazon. It is a book which gives a good overview of Relativity, and how it is more or less given that our universe must be four-dimensional, i.e. containing three spatial dimensions and one temporal dimension. At least that is Petkov's conclusion.

I think Eternalism is a more correct model of the universe than Presentism because of SR and Relativity of Simultaneity, and I agree with the rest of your post. (This is probably the most boring answer of this century ) According to Vesselin Petkov, the experiments confirming SR have also disproved Presentism.

He was probably thinking tenselessly about time, i.e. that all points of time exist on par. In that case, there must be either true or false whether a sea battle happens tomorrow, whether or not we have the ability to predict it using the information within the present point of time. I think the right term for this is logical determinism, and this should be compatible with causal indeterminism in the way you explain in your post above.

Hmm.. Interesting. Thanks for your explaination and the links, Martin! So it actually seems like the universe might be closed, instead of being flat. If this turns out to be the case, then is it possible that the universe is heading towards a Big Crunch in the far future?

Yeah, I see your point. However, from what I have understood of cosmology, the measures of this value have always given results very close to 1, and the universe seems to be accelerating. I am no cosmologist, so I really have no clue other than referring to what I have read. His data is described in the article "Cosmological parameters from SDSS and WMAP" by Tegmark, et al. http://arxiv.org/abs/astro-ph/0310723 (in the table on page 9). I thought the inflationary cosmology was rather strong, compared to many of the other models that exist? It has a great explanatory power, doesn't it?

Really? According to Alan Guth's article "Eternal inflation and its implications" (http://arxiv.org/pdf/hep-th/0702178), the omega constant is found to be approximately 1.012 (+0.018/-0.022), hence the universe seems to be rather flat.

Wow! I was actually thinking of a kangaroo in Denmark, eating an orange!

What I don't get is this: If the "single bounce" scenario is correct, then the universe is (more or less) the same on each side of the Big Bang/Bounce, and hence the universe we have now is almost the same as the universe 13.7 billion years before the bounce. But if this is the case, then the universe must have started exactly like it will end in the future, that is with a "inverse Big Rip". How can a (inverse) Big Rip be the begining of the universe? Or have I misunderstood completely?

∞ is not a constant at all, it's more like a direction. A constant, let's say n, can move towards ∞ (n->∞), or towards -∞ (n->-∞), but it can never BE ∞.

Yes, you're right... I forgot that. (It's fixed now. Thanks for noticing!)

0.999... = 0.9+0.09+0.009+0.0009+... = [math] \sum_{n=1}^{\infty} \frac{9}{10^n}[/math], which is an infinite row. The sum of an infinite row is defined as S=a_0/(1-k), where a_0 is the first number of the row, and k=a_n/a_(n-1). Here: k=0.09/0.9=0.1 and a_0=0.9 => S=0.9/(1-0.1)=0.9/0.9=1 (Q.E.D.) Those who disagree should say where in my calculations I am wrong.

Because some people don't understand what a limit is, and that "..." means the limit where the number of 9s goes towards infinite. I talk from my own experience actually. I was one of those stupid lads who disagreed that 0.99...=1, saying that "no matter how many 9s you place behind the '.', the result will never be exact 1!". I am less ignorant today.