Had a hard time picking out a consistent point being made in that long post, so I picked this little bit out.

It's difficult to believe that such beings would observe events on our planet without instituting the policing that would protect us from eachother. ...as in Clarke's Childhood's End. — Michael Ossipoff

This sort of makes the assumption that we're worth saving. How can a species that has the collective maturity of an ebola outbreak be the thing they want to save? If there's a test, we certainly have yet to pass it.

Does the red-shift seen in the color of light from distant stars represent the distance between us and that star, as in has distance been tightly correlated to that effect through another reliable measure of distance?

Because there's other interpretations, such as a doppler frequency shift due to velocity between us, which looks a bit odd in the face of light-speed is always the same in every frame of reference. — AngleWyrm

Doppler shift, yes. Light is the same speed in any frame. It is not the same frequency or wavelength. Those are frame dependent measurements.
A photon has no objective wavelength or frequency, but a full spectrum beam of light bears the fingerprint of the frame of the source of the light. Hence the speed of some distant star can be assessed by the measurable shift of the light frequency.

I'm not sure about this. I wonder if the principle behind the Boltzmann brain hypothesis can also apply here. It is more likely that an Earth-like planet spontaneously forms than for a Hubble volume to grow and develop as ours is believed to have done. — Michael

Interesting. Perhaps we could define a duplicate as not just a state, but one that persists for a second or so as a natural duplicate should. A Boltzmann Earth duplicate ceases to be a duplicate immediately just like the brain ceases to be a brain in a moment

Does it means that absolute time is some dimension not known or measured by us on this planet?? — vesko

Absolute time is fiction. I can't prove there are no invisible pink unicorns, but I can't detect them either.
To say there is no absolute time is to say there is no detectable actual time of the universe. It is meaningless to say exactly when some supernova occurred in Andromeda galaxy for instance. An arbitrary frame of reference must be presumed to do that. Pretty much any statement without a specified reference frame presumes absolute time and/or space. Absolute time would imply that all events anywhere are objectively ordered and that there is a correct frame, but again, no way to determine that frame if light speed is the same in all frames.
Light speed being the same in all frames is the only empirical evidence that led to relativity. Myttenar's picture of things (somebody is wrong) can be falsified by lightspeed measurements.

Read a good tutorial on relativity, especially some of the initial thought experiments that led to the SR parts, and not just the articles that teach the conclusions. The thinking behind it helps so much, and helps one to drop the ingrained presumption of absolute time.

With the twins, the travelling twin's time is dilated in the Earth frame, but in the space ship frames, it is the Earth twin whose time is dilated and exhibits less duration.

A man can be wrong without creating a paradox. — Myttenar

Who is wrong? The guy who labelled as a paradox the twin-experiment? It is indeed not a paradox. But you're also labelling it a perceptual problem, so again, who's perceptual problem?

↪vesko this is not a paradox but a simple error of judgment on behalf of the twin who perceives the ships' clock to be ticking slower. — Myttenar

OK, you think one of the twins has a perceptual problem. Not so. He sees his clock ticking at normal pace, and he's right. If you assert that he is wrong about this, then please don't explain this stuff to vesko.

can you explain to me what is perceptual problem,if possible with examples. Thanks. — vesko

There isn't one. Everybody is correct about their ages and the durations of their experience. The only problem is the presumption of absolute time, which is something no instrument can measure, and hence has no evidence of existence.

As for A and B series being the same, yes, but both work for a place, even one that moves around. For any place (say where this ping-pong ball is), events are ordered the same way for both series. There is no difference. For two locations (say here and planet Zog), events are ambiguously ordered, both in A and B series. Either way, there is no difference between the series. Neither is an assertion of a metaphysical stance and hence neither is right or wrong. It's just two different ways of referencing the same things.

Who would benefit from hiring a philosopher? The whole point seems to be thinking of things with no practical application. If there is something practical about it, it isn't philosophy, it becomes science. Those guys tend to be ignored as well if they're not talking about immediate benefits.
So what specific contribution do you think a philosopher has to offer?

I agree they are not other universes. — apokrisis

The type-3 ones are also not other universes, for more or less the same reasons.

So spatial infinity would seem to guarantee that there should be an infinity of Earths where you and me are having this exact discussion - plus every other even faintly similar or utterly different interactions. We could be discussing hair-do's, speaking in Korean, typing random sequences. And the fact any of those might be the case would mean that all those varieties of cloned Earths would have to be infinite in number themselves. There would be an infinite number of replica planets with us speaking Korean, etc.

You mean there is a pile of near-replicas to go with each actual replica. Yes. Those aren't so far away, depending on how loose you allow your definition of 'near replica' to be.

There just is no end to the madness once you let actual infinity run riot in your ontology.

You seem to be apeirophobic *. I followed the argument until it was suddenly labelled madness.
* The word seems to mean more fear of eternity, not infinities of the non-temporal sort. So fear of realities that involve infinities. Could find no better word for that.

Anyway, even in a spatially infinite universe, we would presume that it all expands and cools in the same way. And cooling steadily - or in fact, exponentially - removes material possibilities. If every portion of the universe is losing energy density at a shared rate, that means there is only a tiny time window for replica earths to actually form.

Of course. Any replica of Earth would be the exact same age. A replica cannot begin to form by chance for example, centuries from now on the other side of our galaxy.

Even in Euclidean space, as soon as you introduce something to break the symmetry, you already have some kind of "preference." For example, in a universe that is a flat space with one black hole there is an obvious "center." — SophistiCat

That one makes a bit of a hash of the Copernican principle at least. Ossipoff's initial post on the prior page was such a violation, but there is no such principle in the view he was supporting there.

The simplest compact space that would make the point about the Universe being "finitely infinite" would be a sphere.

The story would then not change no matter how big your hubble factor. Or at least not until all that escaping light came back at you from the opposite direction. :) — apokrisis

I comment on something like this earlier. Such a space is not flat, so it would need to be big enough to account for whatever measure of flatness they've made so far. It's enough that there are places that cannot be reached by light from here, ever. So steering things back on topic, that means it has never been a really alien concept that there are undetectable portions of our universe. Are those places other universes? Not like they're discreet with boundaries where one stops and the next starts.

If there is an exact copy of Earth way out there, then there is an exact copy of me on it. Is that guy me? There are arguments to both sides of that question, so "depends" is all that can be said for now.

Oh I see your point. Yes, the torus is orientable. — fishfry

OK, My terminology is wrong. Orientable, yes. There is no obvious origin, hence no actual grid. It is the orienting that suggests a preferred reference frame.

A curved spherical space is not orientable. You'd see a copy of Earth in all directions, or at least you would if light speed was infinite or Earth was polite enough to hold still. With a flat 3-torrid manifold, the nearest Earths in the sky would be in 6 directions, hence the orientation suggestion.

I tried it with a 3-klein bottle and saw my backside reflection. Weird. And yes, no suggested way to look to do that. It is beyond my imagination to see the distorted picture of diverging ray tracing in such a space.

Apologies. I thought your mention of a torus was a typo. Didn't realise it had been introduced into the thread. If we lived in a 3-torus, we would be able to detect that global alignment as you say. — apokrisis

Well, only if the space was smaller than the hubble-sphere (which it very much is in asteroids). You could see the repetitive things line up in certain directions. With larger space, that can't be done. The grid is objectively there but the event horizon is too far away to detect the grid.

Is this true?
— noAxioms

That a manifold is a locally Euclidean object that exists on its own and does not live in an ambient Euclidean space? Most definitely. — fishfry

I should have quoted more.
I meant to ask if there was no grid in the sky if the space was torrid manifold. I then gave the example of the asteroids game which is played on such a manifold, and there is very much a noticeable grid to it, despite the lack of lines painted through the space or the fact that the screen happens to line up with it.

That's pretty mysterious to me. Do you mean that the new universes don't come into existence? Are you saying that they're always there? — fishfry

Not always there. No new thing at all, so nothing to always have been there.
Schrodinger's cat is the best example. The cat is both dead and alive, without the creation of a new cat, one of which doesn't survive. Still one cat in superposition. They've done this with a macroscopic object now. They have a box that holds something that can be seen without aid, and put that thing in superposition, not create a second thing, both of which are in the box.

In math, the idea of a manifold is more abstract than that. When we imaging the 2-torus, like a big donut in space, we imagine the donut embedded in Euclidean three-space. We can use the equations of the ambient space to describe and manipulate points on the torus. — fishfry

Is this true? I play asteroids in a flat 2-torus space, not on the surface of a donut embedded in three-space. If I fly along either axis, I return to my starting point, but if I angle it a little, I don't. The two axes are obvious even if I'm presented only with a circular screen displaying the local area.
This seems to counter what you're saying. There can be a continuous finite 2-space that does not exhibit this property? I can't think of how that would work.

This all has relevance to MWI multiverse hype. The big problem - if you believe in the reality of principles like the conservation of energy, or causal closure, at all - is that MWI violates energy conservation in the most fundamental fashion. That is at the guts of an instinctive objection.

Now if you are not used to taking the materiality of the Universe seriously, then perhaps it is easy just to imagine the free creation of endless worlds, or endless world branches. — apokrisis

MWI is not an ontological stance. No creation of new universes or new material ('somewhere' as fishfry puts it) occurs, and energy conservation laws are safe.
You seem to have a very biased picture of what MWI is. All it states is that any closed system evolves according to Schrodinger's equation.

A locally flat(tish) universe is compatible with some finite topologies, such as a 3-torus. These guys did some serious number-crunching with WMAP data and came to the conclusion that out of several likely topologies that they considered, a certain compact (finite) topology provided a better fit than the infinite flat topology. — SophistiCat

A bit off topic, but I've always noted that the orientation of the three spatial axes (X, Y, and Z) is arbitrary. If there is an actual x axis, which way is it? But if the universe is a 3-torus, all three axes have a preferred orientation, and this defines a preferred frame as well, even if not an inertial one. If the spatial axes are fixed, the temporal one, orthogonal to the others, is fixed as well.
This is only a minor violation of the principle of relativity, but it galls me enough to discount the significant probability of such a finite topology.

NoAxioms and I just had a lengthy conversation disproving this very point. — fishfry

Unconvinced we disproved it. I left convinced that a random stab will hit a zero-probability 'typical number' which are uncountably infinite. There are also infinite specific numbers, and they are countable. An exact copy of Earth is a specific number. The odds of it being never copied in infinite space is thus zero, with certainty. Of course it was also posted that contemporary physics puts a finite size on the universe, which dispells the whole infinite data-set thingy. Still level 1 places, but not necessary a copy of us.

Secondly, the level-1 multiverse only requires a finite universe sufficiently large that light hasn't had time to get from one point to some other point in the age of the universe.

It means there will never be enough time. It requires the expansion to be accelerating since steady expansion still allows light to travel from anywhere to anywhere else eventually.

By the way, I'd expect that if an infinite universe means that there are other civilizations in the universe, then the nearest one is so far away that, for all practical purposes, including communication or transportation, it's the same, for us, as if it weren't there. — Michael Ossipoff

How do you get this? It seems, especially in the context of this thread, to follow from an assumption that other civilizations must be essentially identical to us to be, well, civilizations.

Could there not be any other civilizations in this universe, if the universe is infinite?

You just got finished saying there is an exact copy of us out there, given infinite space.

Maybe, if, as a form of high-tech quarantine, our belligerent and aggressive species, along with its planet, has been re-located into a universe that was specifically designed, by an advanced technology, to not have any life other than us.

This statement is quite a break from the usual stance I've seen from you. You gone all ID on us? Tegmark for instance described a universe not in need of creation, not designed, nor one where we are special.

We need a thread on the Fermi paradox. Much more relevant to this sort of discussion.

Many Worlds is the only known interpretation of quantum mechanics. — tom

Well, you list others, so there are other known interpretations. Support of MWI is growing among physicists, but it has yet to reach a majority. For the record, my opinion rests with the MWI guys, but without a falsification test, it remains an interpretation, not a theory.

Bohmian mechanics - adds hidden variables to QM, thus a different theory. Doesn't work.

Why are hidden variables disallowed? I think you're right actually in that it was proved somewhere that there can be no hidden variables, but its supporters obviously don't think the proof carries weight.

GRW - ads stochastic collapse to QM, thus a different theory. Doesn't work.
Transactional - I really don't care.

These are new ones to me, but again, why does this addition disqualify them?
Copenhagen is not mentioned, and it carries a lot of voting support still.

My personal aversion to most of the other interpretation is non-locality. Bohmian doesn't necessarily have it, but the others do. The ability to alter the past seems a nastier pill to swallow than the (mostly religious) implications of what MWI does to one's biased ideas of personal identity.

It's not impossible. The computable numbers exist. You might hit one. — fishfry

Well, I hit a different one that cannot be hit, so I'm on thin ice to counter this. But having hit this computable number, I must in addition throw infinite coins and come up heads on them all, or else I just got close to it. I don't need to do that with the 'typical number'. Is there a term for that? I made that up.

Getting back to our original point, this is why even if there are infinitely many universes, SOME state must recur infinitely many times, but not necessarily any particular one. SOME person might exist infinitely many times, but probably not you or me. — fishfry

I would suggest 'possibly not'. If someone has infinite copies, I probably do as well. But I must back off the 'definitely' stance.

So at best, the "in an infinite universe there must be two earths" is false in an absolute sense, and is at best a probabilistic argument. Which I think we already agreed on.

Yes

Trying to discredit my own statements.
You take a stab at a number line with a pointer and you will hit a 'typical number' as I call it. That number cannot be expressed with any amount of digits. It has zero probability of being hit, and yet it was hit.
Is that more what you're after?

Edit: I wrote that before reading your last post. Creepy...
No, I would say it is impossible to hit a computable (or expressible) number, except to say 'this one'.

.3333... is not a sequence of random digits with equal probability. It is in fact the decimal notation for 1/3, something that can be expressed in a few characters. A typical real number is inexpressible because it actually is a sequence of random digits, be they base 2, 10, or 37.
If you can express it in finite language, it is not a typical number, it is a special one.

Well yeah, that's my point. You claimed there's a dup earth, I asked you to support your claim, and you have apparently backtracked. Yes? — fishfry

I am told that contemporary models are not of infinite comoving space. Not being an expert, I have no ground to assert otherwise. So yes, I backtracked.

I pointed out that ANY specific infinite sequence has probability zero. Are you unclear on this point? — fishfry

Clear, and it makes no sense. Any infinite sequence cannot be a specific one. That seems to be the point on which we differ. An infinite sequence is not 'some number' any more than its length is.

Which is good, because contemporary physics holds that the universe is finite. — fishfry

If so, the dup-Earth bit kinda falls apart, eh?

In infinite probability spaces, probability zero events may still happen. Suppose you flip infinitely many coins and they come up in any sequence whatsoever: hthhthththththhthttthhthththt... say. A completely random sequence. What's the probability? Well, the prob that flip 1 is h is 1/2. The prob that flip 2 is t is 1/2. Etc. The prob of the first n flips being exactly what they are is 1/2^n, and that goes to zero as n goes to infinity. Every particular sequence has probability zero. Do you follow that point? — fishfry

No, disagree with this. A finite sequence has a nonzero probability. An infinite one is not a specific one, and has probability zero and does not happen.
Every particular sequence has half the probability of the flip sequence of one-less flip. That is not zero. Some probability-zero sequence is not a particular sequence and thus does not in fact occur.

A 3-manifold, e.g. a 3-sphere, is finite with no edge. — tom

Good point.

It is psychologically interesting that people generally accept the existence of the Type 1 multiverse, when there is absolutely no evidence for it. I'm not sure if evidence for it is even possible? — tom

Isn't just a curvature measurement enough? If flat enough, there are places sufficiently separated to never interact. Yes, expansion is required for that, but not infinite space.

First, why is the space infinite? Your premise is that the universe is finite but sufficiently large that there are regions inaccessible to each other due to light not having had enough time to get from one place to the other. That doesn't require an infinite universe. — fishfry

Indeed, it doesn't require infinite space. It (a type 1 world, not a duplicate) does at least require an expanding universe, else eventually light would have time to cross the distance. The dup-Earth requires space big enough to form duplicates of something, which could in theory be close enough to be visible from here once light had time to make the trip. That is more probable than what you show below where it by chance just never happens.

Secondly, even if the universe is finite AND the possible states in a given region of space are finite, you STILL are not guaranteed a duplicate earth. Say there are two states, and infinitely many universes:

0, 1, 1, 1, 1, 1, 1, ...

Not guaranteed, no. A coin may flip tails forever. It's just a probability after enough distance.

Edit: I think that mathematically, a coin cannot come up tails forever. There cannot not be a dup Earth given infinite space. The probability of of that is 0.000... which is zero.

Again thought, you're betraying your original premise. You started with TWO regions of the universe that are causally and informationally isolated from one another. That's two, not infinitely many.

Not sure I follow this. If there is a duplicate, there would seem to be an infinite number of them. There is simply a probability as to how far away (measured in non-linear units) the nearest one is. There are infinite type-1 worlds given infinite universe size. In fact, each point in space is centered on such a world, so you are in a different one than I am. Light can in theory reach (immortal) you from your slightly-left-shifted world but never reach me in mine. That means that by the time the light gets to you, the expansion of the universe separates us so far that we're forever isolated from each other.

That would not seem to follow, since no distance is infinite. — Janus

Models say otherwise. For the distance to be finite, there would need to be an edge where there is stuff only on one side, and not uniform as we see it. This is true of a subjective model (one with a frame and a 'current event'), but not of any objective view. Other-worlds is necessarily a description from the outside.

How does the second sentence follow from the first? Do the universes share the same history? Why should they do that? — fishfry

They're not separate universes (especially types 1 and 3), just separate worlds in this universe. For type 1, the distant Earth is a true duplicate. The space is infinite, but the possible states in a finite space (say that of Earth) are not, so each state much eventually be duplicated given enough distance.

The same objection that Apo applies to Type 3 is relevant to type 1. Those distant hubble-spheres are just other (sometimes identical) solutions to the same equations. In both cases, there is no separate ontology to it. There is only the one universe, and not a multiverse of separately existing noninteracting things.

For those of us who prefer not to sit through a video, and who have only a nodding acquaintance with the topic, can you please remind us what a level 3 multiverse is? — fishfry

It is a Tegmark designation, and I'm not sure how much the video gets into it. Type (or level) 1: Places that are too distant to causally interact with here, ever. There is a duplicate Earth out there if you go far enough. Type 2 is other bubbles in eternal inflation theory. Those bubbles all have the same QM, but different dimensions, light speed, and other physical constants. There is a duplicate Earth there as well. Type 3 is Everett multi-worlds, essentially parallel-here. Type 4 is other structures altogether, and it is hard to argue that they're not separate universes, but ours exists no more than those others.

I didn't watch the linked video. For the record, quantum mechanics does not say the multiverse is real or is not. Not sure what 'physics' is wrong or conflicts with QM.

I think different people have different definitions of what 'is real'.
One can view the universe from within or from without and yield different answers to the same questions, and nobody is wrong or right.
So from within, only what we can sense or what possibly can effect us is real. It is not wrong to say there is no multiverse. From an objective view, there may be multiple worlds, but still one universe. These two different ways of looking at it are completely valid for not just Type 3, but also types 1 and 2.

So it seems there is no multiverse, but only because that is a poor choice of words. Everett proposed one universe with different solutions to measurements, but no 'collapse' that makes one of those solutions the actual one. That's multi-world perhaps, but not multiverse.

There doesn't seem to be a law that cleary demonstrates true regularity of any physical process. — TheMadFool

Yes there is such a law, and it is used in the articles linked. They've demonstrated the accuracy of some clock to X digits, and not by using a more accurate one.
You seem to just want to deny any answer to your query. So what's your purpose in asking then?

Every object has a separate now attached to it as a property. — guptanishank

OK, we're taking completely different things then. Ignore what I've said.

Could you explain all of this in a little more detail. I would love to get to the bottom of this. Thanks.

I know the model is mathematically consistent. The interpretation is after all, built on top of the math.
That's not the point I was trying to make. Time CANNOT be defined for all the objects this way, because of mathematical restrictions. It would be counter intuitive to say the least, that a now is not defined for every object as well. — guptanishank

Not sure what all else to explain. A photon, or anything else with no rest-mass, is missing half the properties of a classic object due to the inability to be at rest in any frame.

So every theory, built upon this concept of time, will not have a now for every object, because time itself was not defined for those objects, and we are trying to build a theory of now from the current concept of time.

This part confused me since no object has a 'now'. Events do, and 'now' is only a self-reference to that event. Pair an event with any other event and the two events can be said to have pure spatial separation (temporally simultaneous) or pure temporal separation (spatially the same place) by aligning one of the axes to go through both events. If you don't think axes can be arbitrarily assigned, I ask where any of them are? Which direction is the X axis of the universe? There isn't one. There isn't a temporal one either. Choosing one is arbitrary, as per the principle of relativity, which is older than Galileo's work, even if the implications of that principle weren't worked out until a century ago.

The problem with that specific definition is that time is not defined for light. Light has no frame of reference, and hence no time or space associated with it. — guptanishank

Exactly so. Light has no frame, travels in no specific direction, cannot rest, has no mass and exists in no time of its own. But all these things are defined by arbitrary selection of frame.
Light doesn't exist inside or outside a causal cone, but rather occupies the dimensionless singularity where the rotation of one type of dimension becomes the other type. Quite consistent with the mathematics of it all.

This definition/description does not seem to require causality? — guptanishank

Causality is what distinguishes the temporal dimension from the other ones.

if you are in a space ship somewhere in the universe and you have no clock, how can you measure the time with some approximation? — vesko

the answer is as follows :
simple way can be the measuring of our pulse which is a given by God interval we can use to measure the time . — vesko

If you have a pulse, you have a clock. Lousy precision, but a clock nevertheless. You can time the boiling of your egg by counting heartbeats.

So the time is nothing else but a counting of repeated events done by humans. — vesko

The counting can be (doesn't need to be) done by humans. The counting is not what time is. It is simply a human taking a measure of what time is. Plenty of non-human things utilize time measurement.

Plus distance is only applied for space. How are you defining distance for time. — guptanishank

In the spacetime model, the temporal dimension is distance just like the other three. There is physical distance between any two events, and that distance is temporal only if the two events are inside their mutual light cones. It is spatial only if the two events are outside those cones.

How do we know that? My watch's error can be detected by an atomic clock. How do we detect the error of an atomic clock? — TheMadFool

Read the links fdrake posted. They answer exactly this question. At the sort of accuracy they're talking, two clocks would need to be in exactly the same environment. Put them in adjacent parking spaces and the difference in latitude will get them out of sync.

So the negations of both versions of the sentence would be "Caesar is not a prime number"(which seems sensible) and "Caesar is number that is not prime." (which is bonkers) — jospehus

You were doing fine until here. That was not the negation.
The negation of the latter sentence is "Caesar is not a number that is prime".

but what if the time irregularity is in the nanoseconds or femtoseconds? — TheMadFool

I think you ask about what if the radioactive same ticked regularly. Then the decays would not be random events, but regular ones. All similar-rate samples would tick in sync. They don't. No way at all to predict when the next tick will come or which sample will yield the next tick.

My example used whole numbers and the error reveals itself quite easily but what if the time irregularity is in the nanoseconds or femtoseconds? Errors at such scales can be detected only over millions of years, right? — TheMadFool

My counter example works fine with nanoseconds. The radioactive samples might tick every nanosecond and the example still holds. The two samples would not be in sync ever, and thus are not representative of actual time. The decays are random events, much in the same way that Earth rotations are not.

Look at the history of time measurement. Started with the sun, moon and earth - wasn't accurate enough. Then we moved to pendulums - wasn't accurate enough. Now we have atomic clocks - aren't perfect. Isn't this the infinite regress I'm suggesting here?

Sun movement is way more accurate than pendulums, but inaccurate in the long run. The day used to be a lot shorter.

I see no infinite regress, or even finite. Yes, some things are more regular than others, radioactive decay being probably at the low end of the scale. Such accuracy is not needed except to verify very fine differences. You apparently don't accept that. You seem to assert that time cannot be known without some insanely accurate device. But somebody said that a day is defined as the time from noon to noon on some arbitrary day in say 1900, and that's the standard, period, even if we don't know how to translate that value into Caesium vibrations (something even more stable than Earth) to twelve places until decades later.