Do we live in 3 or 4 dimensions?

[Stricklandjr]

Check out page 15 in Schutz. Curves on which $-t^2+x^2$ is constant look the same in all coordinate systems. So if you pick a point on the t axis that's 1 second away from the origin, and follow such a hyperbola from that point to the point where it intersects the t' axis, you have found an event that is 1 second away from the origin in the other coordinate system.

Thank you Fredrik. I used up my previewing on Schutz before getting through that but I get an inkling of what it is so I'm going to put your formula into an Excel spread sheet and graph it out. I've also been starting to look in my algebra book and am going to study the hyperpola. I never thought I liked math but now I'm beginning to think it might be cool after all if it can show me how the universe works.

 

[Stricklandjr]

same time in spacetime

OK. You guys got me doing more homework than I ever did in jr. college physics and algebra classes. But this is really getting to be neat stuff. I feel like I'm being a physicist. So I played around with the hyperbola graphs in Microsoft Excel and came up with this one after going thru Shutz and going back to some things Dr. Donis said about slices and came up with a slice. What's amazing is how the slice explains why the moving guy sees an earlier time on my clock world tube (don't worry I know that you have to take into account how much time it takes for light to get there before you can see and I don't care about that right now because these basic ideas are what's really got my brain spinning). You were really putting me in the right direction Mr. Fredrick when you said to dig into spacetime pictures thank you.

I marked times t1 t2 and t3 to show these times are all the same since they are on the hyperbola. t4 is the time on my world tube clock that the moving guy would see in his slice of 4dimensional spacetime that Dr. Donis told me about. I really used ct for the time axis to get the units suggested by Mr. Fredrik.

Now I can't say this for sure but it looks like the space direction for the moving guy is always going to be a tangent line to the hyperbola.

 

[Stricklandjr]

I'm really have to study hard on something now because something don't seem right here. On the one hand people here are saying that I am moving along the 4th direction all the time. But when I look at the spacetime diagram then nothing is moving because everything is a 4 dimension world tube and the tubes are not moving anywhere. So was my thinking all wrong? Maybe the spacetime is 4 dimensions and I am 3 dimensional moving through the 4 dimensional spacetime? I'm reall sorry for getting this mixed up after I thought I was really getting it but now it looks like the world tubes can't be moving.

I still remember what Dr. Donis said: So you can't really view the object as a 3-dimensional thing that moves through time; you have to look at its entire 4-dimensional world tube"

But how do we move through time? It seems like I can feel myself moving through time but when I look at my world tube it doesn't move.

 

[PeterDonis]

it looks like the space direction for the moving guy is always going to be a tangent line to the hyperbola.

Yes, that's correct. You can actually prove this mathematically.

 

[PeterDonis]

I'm really have to study hard on something now because something don't seem right here. On the one hand people here are saying that I am moving along the 4th direction all the time.

For an appropriate sense of the term "moving", yes. See below.

But when I look at the spacetime diagram then nothing is moving because everything is a 4 dimension world tube and the tubes are not moving anywhere.

Yes, that's right. What you have here are two different ways of looking at the same physics:

If you are trying to make sense of what a person following a particular worldline/world tube is experiencing, you have to have some way of talking about his experience of "moving" through time--he doesn't experience his entire 4-dimensional world tube all at once. So you have to talk about things like 3-D cross sections, bearing in mind that these are abstractions, and only approximate ones at that.

But if you are looking at the entire spacetime history, for example when you draw a spacetime diagram, you are looking at the entire 4-dimensional thing all at once. On this view, as you say, nothing "moves" at all; the entire 4-dimensional thing is just there.

Both of these views are correct; they are, as I said above, just different ways of looking at the same physics. As far as what things are "really like", I (and many others here) would say that's a question of philosophy, not physics.

 

[Stricklandjr]

For an appropriate sense of the term "moving", yes. See below.



Yes, that's right. What you have here are two different ways of looking at the same physics:

If you are trying to make sense of what a person following a particular worldline/world tube is experiencing, you have to have some way of talking about his experience of "moving" through time--he doesn't experience his entire 4-dimensional world tube all at once.

I probably don't understand this Dr. Donis. I feel like I have let you down after all of the knowledge you and Mr. Fredrik have offered me. Does it me he is really a 4 dimensional world tube but he just experiences one slice at a time?

So you have to talk about things like 3-D cross sections, bearing in mind that these are abstractions, and only approximate ones at that.

I am afraid I don't know what this abstraction is. I'm sorry to disappoint you. I think I understand cross sections though.

But if you are looking at the entire spacetime history, for example when you draw a spacetime diagram, you are looking at the entire 4-dimensional thing all at once. On this view, as you say, nothing "moves" at all; the entire 4-dimensional thing is just there.

Yes. You are saying it just like I was trying to. The entire 4 dimensional thing is just there. So I still need to understand how it could be moving.

Both of these views are correct; they are, as I said above, just different ways of looking at the same physics.

I'm sorry for being slow and don't mean to repeat but are the two ways, one way is a 3 dimensional guy moves through spacetime and the other way is the guy is a 4 dimensional world tube. But it seems like if its a 3 dimensional guy moving through spacetime then the slices don't work anymore but if it's a 4 dimensional world tube nothing can move.

As far as what things are "really like", I (and many others here) would say that's a question of philosophy, not physics.

Are you saying that you physicists can't know what it's really like and I have to study philosophy to know what is really going on with the universe? My cousins buddy told me I was too dumb to understand the universe and it's beginning to look like he might be right. I guess I'm getting out of my element. My daddy told me if things didn't work out I could come back to the farm. But I know I don't want to do philosophy, they would have me trying to dance on the head of a pin.

 

[PeterDonis]

Does it me he is really a 4 dimensional world tube but he just experiences one slice at a time?

No, it means that the question of what he "really is" is a philosophical question, not a scientific one. (At least, IMO it is.) See further comments below.

I am afraid I don't know what this abstraction is.

Sorry, I should have been clearer. What I mean is that, as I said in a previous post, the cross section is not something anyone directly observes, because of light speed time delay. We experience objects as 3-D things that move in space and exist for some length of time, but our brains construct that experience from the actual data; the actual data is the light that we receive from objects, and that light is time delayed. It's just that the time delay, under ordinary conditions, is much, much smaller than any length of time we can consciously perceive, or even that our nervous systems can detect.

For example, if an object is 1 meter long, it takes light 3.3 nanoseconds to travel the length of the object, so the light you are seeing at a given instant from the object's far side was emitted 3.3 nanoseconds before the light you are seeing at the same instant from the object's near side. But your neurons have a cycle time of something like 20 milliseconds, more than a million times longer than that 3.3 nanoseconds, and you can only consciously perceive time intervals of around 100 milliseconds or longer, almost ten million times longer than that 3.3 nanoseconds.

So under ordinary conditions the light speed time delay is undetectable. But it's still there, and that means that the 3-D cross sections in our mathematical model are not directly observed; we have to construct them by extrapolating forward from the time-delayed light signals we receive. The same goes for the 4-dimensional world tubes in general; we don't directly observe them, we have to construct them in our mathematical models based on the data we have.

Yes. You are saying it just like I was trying to. The entire 4 dimensional thing is just there. So I still need to understand how it could be moving.

It isn't. If you view an object as its entire 4-dimensional world tube, it doesn't move; it's just there. But you don't experience it that way, so if you want to talk about your experience--and after all, if we're going to talk about experimental results, we have to talk about our experiences of them--you can't just talk about 4-dimensional things that are just there, because that's not what we experience. You have to talk about things moving, since that's what we experience; and that means you have to have a second way of looking at the physics, in addition to the 4-dimensional way, if for no other reason than to be able to translate what the 4-dimensional model says into predictions about what people will actually experience.

it seems like if its a 3 dimensional guy moving through spacetime then the slices don't work anymore but if it's a 4 dimensional world tube nothing can move.

The two ways are not two different ways the world can be, one of which is true and one of which is false. Both ways are valid; they are just different ways of looking at the same physics, as I said before.

Are you saying that you physicists can't know what it's really like

No; physicists are not limited to considering just physics questions, any more than anyone else is. And even if knowing the physics doesn't necessarily tell you "what it's really like", knowing the physics is certainly not irrelevant.

and I have to study philosophy to know what is really going on with the universe?

That depends on your attitude towards philosophy. My personal view is that the only thing that studying philosophy will do for you is to help inoculate you against the claims of philosophers to "know what is really going on". IMO, *nobody* knows what is "really going on"; how could we expect to? It's a wonder we know as much as we do. But maybe that's just me.

At any rate, the main point I was really making is that PF is a forum for discussing physics, not philosophy; so when people start trying to talk on PF about "what is really going on", as opposed to actual physical theories or actual experimental results, the discussion quickly gets bogged down. It's better to focus on the actual theories and the actual experiments.

My cousins buddy told me I was too dumb to understand the universe and it's beginning to look like he might be right.

I suspect your cousin's buddy is in worse shape than you on that score; at least you came here and asked intelligent questions.

I guess I'm getting out of my element.

Don't give up too easily. This stuff is counterintuitive; it's not supposed to just instantly ring true to you. It didn't to me at first either. I've been studying this stuff for many years; so have most of the experts here.

But I know I don't want to do philosophy, they would have me trying to dance on the head of a pin.

As you can see from the above, I agree with you. But you should realize that avoiding philosophy, which is IMO a good idea, also means avoiding questions that we all feel an urge to ask but which don't have any real meaning if you're avoiding philosophy, like "what is it *really* like?"

 

[Fredrik]

Does it me he is really a 4 dimensional world tube but he just experiences one slice at a time?

An object's entire existence is something 4-dimensional. Specifically, it's a bunch of curves in spacetime that describe the object's motion. Each curve describes the motion of a component particle. But if I mention my car, you won't assume that I'm referring to a set of timelike curves in a 4-dimensional spacetime. You will assume that I'm referring to the 3-dimensional thing that's parked outside my house right now. "Now" is the key word here. "Space, right now" is a 3-dimensional slice of spacetime. My car's entire existence is represented by a set of curves. But my car (and by that I mean "my car, right now") is represented by the set of points where those curves intersect that slice. That's a 3-dimensional region of spacetime.

Note that in a spacetime diagram, the slices that we can think of as "space, at time t" are horizontal lines. The world tube you've drawn will intersect those slices at different x coordinates. In relativity, that's what motion is, nothing more, nothing less.

Are you saying that you physicists can't know what it's really like and I have to study philosophy to know what is really going on with the universe?

Yes to the first part, and no to the second part. Physicists don't always know what things are really like, but when they don't, philosophers don't either. Physicists do experiments to find out how accurate a theory's predictions are. This way they can eliminate the bad theories. But a theory may be consistent with more than one idea about "what's really going on", and in that case, no one will know what's really going on. Each attempt to interpret a theory is philosophy, and the thought process that you have to go through to understand that is philosophy.

Oddly enough, this doesn't mean that physicists who want to understand these things better can just pick up a philosophy book.

 

[TheBC]

.Always interesting to read what Einstein himself was thinking of all this:

<< From a "happening" in three-dimensional space, physics becomes, as it were, an "existence" in the four-dimensional "world". >> Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's Four-Dimensional Space ("World") (supplementary to section 17 - last section of part 1 - Minkowski's Four-Dimensional Space).

<< Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> Albert Einstein, "Relativity", 1952.

 

[Stricklandjr]

.Always interesting to read what Einstein himself was thinking of all this:

<< From a "happening" in three-dimensional space, physics becomes, as it were, an "existence" in the four-dimensional "world". >> Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's Four-Dimensional Space ("World") (supplementary to section 17 - last section of part 1 - Minkowski's Four-Dimensional Space).

<< Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> Albert Einstein, "Relativity", 1952.

Boy! Mr. TheBC you are really giving us some real important sayings of Einstein. It seems like he really did think that the universe and things are 4 dimensional all there at once. I think this is very big news and Mr. Fredrik and Dr. Donis will really be interested to hear about this. You have made some very important information to our discussion.

I think maxverywell could really use your knowledge on his post because he had some of the same puzzling about moving in time and the 4 dimensional universe.

 

[Stricklandjr]

Other Theory

I was trying to go back through the information given by Mr. Fredrik and Dr. Donis to know more about why they wouldn't agree that what Einstein said. I mean they really agreed but had to say that you couldn't know it for sure because the real 4 dimensional universe with slices is philosophy. One thing I saw in Mr. Fredrik's information was that it may not be real because there is another theory that says it is not really a 4 dimensional universe all there at once.

Mr. Fredick pointed out that: "But a theory may be consistent with more than one idea about "what's really going on", and in that case, no one will know what's really going on."

But he didn't say what the other idea is that would be different from the 4 dimensional universe all there at once. What is the other theory?

 

[PeterDonis]

I think this is very big news and Mr. Fredrik and Dr. Donis will really be interested to hear about this.

I'm well aware of these sayings of Einstein, thank you. I'm sure Fredrik is too. Bear in mind that Einstein in those passages was not talking about the physics; he was talking about his interpretation of the physics. In other words, what he was saying was really philosophy, not physics. His philosophy is certainly consistent with the physics, but it's still philosophy.

 

[Fredrik]

...the real 4 dimensional universe with slices is philosophy. One thing I saw in Mr. Fredrik's information was that it may not be real because there is another theory that says it is not really a 4 dimensional universe all there at once.

Mr. Fredick pointed out that: "But a theory may be consistent with more than one idea about "what's really going on", and in that case, no one will know what's really going on."

But he didn't say what the other idea is that would be different from the 4 dimensional universe all there at once. What is the other theory?

The 4-dimensional spacetime is part of the definition of SR, so this is not the sort of thing I had in mind. I was thinking about attempts to get something out of the theory that isn't really there. For example, the theory says that if your twin goes on a space voyage and travels close to the speed of light relative to the Earth, he will be significantly younger than you when he gets back. SR tells you how to calculate his final age and your final age, but it doesn't tell you why the calculations should be done that way. Someone who wants to explain it could try to say things like this:

a) Space is filled up with a substance called the ether. Clocks at rest relative to the ether tick at their maximum ticking rates. A clock moving with velocity v relative to the ether is slow by a factor of $\gamma=1/\sqrt{1-v^2}$ because of its interactions with the ether. An observer equipped with such a clock will still measure the speed of light to be 1, because every object that's comoving with him (in particular the meter stick he uses to measure distances) will be contracted by a factor of $\gamma$ due to interaction with the ether.

b) Motion doesn't affect the ticking rate of clocks at all. There is simply "less time" to be accumulated along the astronaut twin's path through spacetime from the departure event to the return event.

I would say that b) is the natural and straightforward interpretation of SR, and that a) is an old-fashioned idea that shouldn't be encouraged. But it would be unscientific of me to say that b) is correct and a) is wrong, because neither of these assumptions has any falsifiable consequences. So there's no experiment that can support that claim.

 

[PeterDonis]

I mean they really agreed but had to say that you couldn't know it for sure because the real 4 dimensional universe with slices is philosophy.

...

What is the other theory?

Fredrik has given a good response, but I'd like to give a few other reasons why I am careful about making claims about what things are "really like":

(1) We know that special relativity is only an approximate theory; it is only strictly valid in the complete absence of gravity, and in the universe we observe there is gravity present everywhere to some extent. So the Minkowski spacetime that we use in SR is certainly not an exactly correct model of what things are "really like".

(2) The obvious response to #1 is that general relativity, which does deal with gravity, also uses 4-dimensional spacetime; it just allows that spacetime to be curved, whereas SR assumes that it is flat. However, we know that GR is not a complete theory, because it doesn't include quantum mechanics. And once we include quantum mechanics, it is highly likely that the concept of "spacetime" as we use it in GR is no longer fundamentally valid--that at some very small scale, of the order of the Planck length/Planck time, our model of spacetime as a smooth 4-dimensional manifold will break down. So even the general curved spacetime that we use in GR might not be an exactly correct model of what things are "really like".

(3) Even if we ignore #1 and #2, there is still a big problem with making claims about the entire universe based on 4-dimensional spacetime models. When we talk about a made up scenario, we stipulate what is in it. We can draw a spacetime diagram that contains everything that is in the scenario, as far in the past or future as we like, extended as far in space as we like, because we made up the scenario so we get to declare by fiat what is in it.

But in the real universe, we can't do that. People talk about what is happening in the Andromeda galaxy, say, "right now", as if it were something we knew directly, or at least something that is such an obvious, certain extrapolation from what we know directly that it's basically the same thing. But it isn't. The best information we have from the Andromeda galaxy, the light that is just now reaching us from there, is 2 million years out of date. Lots of things could have happened there that we don't know about. I don't just mean that stars could have exploded, another galaxy could have collided with it (from the "back side", the side we can't see), or aliens could have taken it over and rearranged all the stars in an orderly square array. I mean that, say, some quantum phenomenon could have changed the very nature of "reality" there--say some kind of phase transition similar to the ones that happened in the early universe--so that 4-dimensional spacetime is no longer even a good model of it any more.

But, you say, surely that sort of thing can't happen? Well, it seems highly unlikely based on what we currently know. But what we currently know is extremely limited. It doesn't seem that way to us because we've expanded our knowledge so much in the recent past. But that just means we've gone from being colossally ignorant to just being extremely ignorant. So when I see people, even physicists, proclaiming that "the universe is a 4-dimensional manifold that exists all at once" as though it were a proven fact, or the next thing to it, I just sigh and remind myself that even very smart people can have trouble distinguishing what is known from what is just speculation--reasonable speculation, speculation that's consistent with what we know, but still speculation.

 

[Stricklandjr]

Lorentz Ether Theory

Mr. Fredrik and Dr. Donis I understand now that you both already knew about what Einstein said and that he was not saying it as a physicist but was being a philosopher. You have both pointed out many things so I have to study some more on all that.

Please do not think I am starting an argument because you two have taught me much about relativity but one thing I noticed when Mr. Fredrik was telling about two theories: a) ether theory and b) 4 dimensional universe all there at once. I don't think ether theory could be used to call Einstein's statements into disrepute because of what I read the other day when I signed up in the physics forum and agreed to the rules given by Mr. Greg Bernhardt. Mr. Greg Bernhardt said: "Generally, in the forums we do not allow the following:

Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory);

So I don't think ether theory should be used on this forum to contradict Einstein."

 

[TheBC]

Mr. Fredrik and Dr. Donis I understand now that you both already knew about what Einstein said and that he was not saying it as a physicist but was being a philosopher. You have both pointed out many things so I have to study some more on all that.

Please do not think I am starting an argument because you two have taught me much about relativity but one thing I noticed when Mr. Fredrik was telling about two theories: a) ether theory and b) 4 dimensional universe all there at once. I don't think ether theory could be used to call Einstein's statements into disrepute because of what I read the other day when I signed up in the physics forum and agreed to the rules given by Mr. Greg Bernhardt. Mr. Greg Bernhardt said: "Generally, in the forums we do not allow the following:

Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory);

So I don't think ether theory should be used on this forum to contradict Einstein."

Very interesting and important comment you made there, Stricklandjr.

SR - 4D SPACETIME -BLOCK UNIVERSE -ETHER THEORY have been discussed a few times on PF.

Check out these threads for a start. (Along the way you will also encounter some very nice (Loedel) 4Dspacetime diagrams that help visualize what's going on):

https://www.physicsforums.com/showthread.php?t=685960&page=2

https://www.physicsforums.com/showthread.php?t=595021#post3857706

https://www.physicsforums.com/showthread.php?t=583606

https://www.physicsforums.com/showthread.php?t=561344&highlight=block+universe

a.s.o.

A lot to digest. Good luck.

 

[Stricklandjr]

More to study on

Thank you Mr. TheBC for giving me all of those other posts to study on but now I see it will take me much time to understand all of this. My cousin is going to loan me his book about The Fabric of the Cosmos and I think that will help me understand more about this. I am excited to find out about the new diagrams because now I can compare distances and times without having to draw so many hyperbolic curves in Excel (but I like doing that anyway) but I think my mother will fuss at me again if she finds out how much time I spend doing graphs in Excel. I think you are right about ether and I don't think it should be used to contradict Einstein and that's what Mr. Greg Bernhardt warned us about too. I think you are giving me a new word for Einstein's 4 dimensional universe you call it the block universe. I think Mr. Fredrik or Dr. Donis called it Minkowski spacetime.

 

[PeterDonis]

I don't think ether theory should be used on this forum to contradict Einstein."

We weren't contradicting Einstein; we were pointing out that the statements of his that you quoted were philosophy, not science. The same is true for "ether theory", at least as it's usually understood here: it is not a different theory from standard SR, it's just a particular interpretation of what standard SR "means". The "block universe" is another such interpretation. But since all of these interpretations predict exactly the same results for all experiments, whatever difference there is between them is a philosophical difference, not a scientific difference.

 

[PeterDonis]

My cousin is going to loan me his book about The Fabric of the Cosmos and I think that will help me understand more about this.

It might, but it might also induce more confusion. Bear in mind that The Fabric of the Cosmos is not, strictly speaking, a science book; it is a pop science book, which is not the same thing. We get threads here quite often started by people who are confused by things Brian Greene says in his books; IMO it's because Greene is not really trying to give a consistent, scientific presentation of the material, he's just trying to sell books. It's not that the things he says are wrong, exactly; but a lot of the things he says are not intended to help people actually learn the science, they are intended to make people say "wow, neat!" and tell all their friends how neat the book is, without ever having actually learned the science. (Of course this is just my opinion, but it comes from reading both The Elegant Universe and Fabric of the Cosmos, seeing all the threads here on PF about them, and also understanding the science Greene is talking about. Still, your mileage may vary.)

I am excited to find out about the new diagrams because now I can compare distances and times without having to draw so many hyperbolic curves in Excel

Um, you should realize that Loedel diagrams *are* spacetime diagrams; they are just spacetime diagrams drawn in a particular frame that is chosen to make the diagrams "easier" to use (for some people's definition of "easier"). But in order to properly mark off distances and times on the Loedel diagram's axes, you still have to draw the hyperbolas.

 

[phinds]

It might, but it might also induce more confusion. Bear in mind that The Fabric of the Cosmos is not, strictly speaking, a science book; it is a pop science book, which is not the same thing. We get threads here quite often started by people who are confused by things Brian Greene says in his books; IMO it's because Greene is not really trying to give a consistent, scientific presentation of the material, he's just trying to sell books.

+1 on that !

 

[TheBC]

Just a thought: Maybe Brian Greene simply does not want to spend time on an ether that has never been detected the last 500 years and is considered superfluous in Einstein's Special Relativity:
<< The introduction of a “luminiferous ether” will prove to be superfluous inasmuch as the view here to be developed will not require an “absolutely stationary space” provided with special properties,... >> On the electrodynamics of moving bodies, by A. Einstein, 1905. http://www.fourmilab.ch/etexts/einstein/specrel/www/

 

[PeterDonis]

Maybe Brian Greene simply does not want to spend time on an ether that has never been detected the last 500 years and is considered superfluous in Einstein's Special Relativity

I think you're misunderstanding my point. My point is not that Greene ought to talk about ether theory as an alternative to the block universe. I've already said several times that both of these are not scientific theories, they're philosophical interpretations.

My point is that Greene's books (and his TV specials) are not scientific books; they're pop science books. They might be fun to read/watch, they might have a good "wow!" factor for people who aren't really interested in learning the science but want to be entertained; but they are *not*, IMO, good sources if you actually want to learn about physics--the actual scientific theories that underlie the stuff Greene talks about.

Greene's talk about the "block universe" is a case in point. A person who didn't know better would be strongly tempted to conclude, from what Greene says, that the "block universe" is a scientific theory, not a philosophical interpretation. The way to fix this is not to talk about ether theory as an alternative interpretation; the way to fix it is to admit the key distinction between actual scientific theories and philosophical interpretations of them. Greene never does this; he never even gives a hint that it's an issue.

 

[Dale]

.Always interesting to read what Einstein himself was thinking of all this:

<< From a "happening" in three-dimensional space, physics becomes, as it were, an "existence" in the four-dimensional "world". >> Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's Four-Dimensional Space ("World") (supplementary to section 17 - last section of part 1 - Minkowski's Four-Dimensional Space).

<< Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> Albert Einstein, "Relativity", 1952.

I always appreciate when you go out of your way to highlight all of the words like "exist" and "reality" that indicate that it is a philosophical (ontology) quote.

 

[Stricklandjr]

Just a thought: Maybe Brian Greene simply does not want to spend time on an ether that has never been detected the last 500 years and is considered superfluous in Einstein's Special Relativity:
<< The introduction of a “luminiferous ether” will prove to be superfluous inasmuch as the view here to be developed will not require an “absolutely stationary space” provided with special properties,... >> On the electrodynamics of moving bodies, by A. Einstein, 1905. http://www.fourmilab.ch/etexts/einstein/specrel/www/

Mr. TheBC I'm glad you told us about this saying of Einstein because it shows why Greg Bernhardt told us the rule about not bringing up ether theory on this forum. Now people can't say that the 4 dimensional spacetime all at once can't be a correct theory because there is another one called ether theory that is just as good. I think you should be a Dr. like Dr. Donis because you know so many sayings of Einstein.

 

[phinds]

Mr. TheBC I'm glad you told us about this saying of Einstein because it shows why Greg Bernhardt told us the rule about not bringing up ether theory on this forum. Now people can't say that the 4 dimensional spacetime all at once can't be a correct theory because there is another one called ether theory that is just as good. I think you should be a Dr. like Dr. Donis because you know so many sayings of Einstein.

You really seem to be missing the point.

 

[Dale]

Now people can't say that the 4 dimensional spacetime all at once can't be a correct theory because there is another one called ether theory that is just as good.

The reason it can't be a correct theory is because it isn't a theory, it is an interpretation.

 

[TheBC]

Why would SR be a theory and not LET?
What you in fact mean is that the Lorentz Transformations are one thing, and ether and block universe are two different interpretations of the calcultations.
In that case SR and LET are two interpretations of the Lorentz Transformations, and thus the ether definitely not an interpretation of SR.

It then boils down what you consider a theory and what an interpretation.
Scientific theory includes a series of statements about the causal elements for observed phenomena, which makes LET a theory, not an interpretation. And 4Dspacetime makes SR a different theory.

On this forum it seems that a formula is sufficient to call it a theory, and all the rest is philosophy! But then we should talk about a "Lorentz Transformation Theory", with SR and LET (block and ether) as 'interpretations' of that theory. That's a far cry from stating that the ether is an interpretation of SR.

 

[Dale]

What you in fact mean is that the Lorentz Transformations are one thing, and ether and block universe are two different interpretations of the calcultations.

Yes. And SR, as a theory, is the Lorentz transform (with its experimental interpretation).

For some reason you keep trying to equate SR with the block universe interpretation, but the block universe is outside the theory and is only an interpretation.

Scientific theory includes a series of statements about the causal elements for observed phenomena, which makes LET a theory, not an interpretation. And 4Dspacetime makes SR a different theory.

Then, if they are different theories, please provide one experiment which could, in principle, distinguish between the two.

 

[Stricklandjr]

Ideas on 4 dimensional universe physics

We played pool Saturday night and then went to Ray's Bar-B-Q and
had a big bull session about relativity. No one could believe
all the things I learned about relativity and the my cousin and
Frank got into another big argument about whether the universe
was 4 dimensional all at once and it seemed like they were getting
a little angry. Frank said that ether theory didn't have anything
to do with it but the universe is just 3 dimensions and is always
changing and that the 4th dimension is just for mathematics
calculations. I told my cousin that some people said the the
4 dimensional universe all there was just philosophy and not real
physics but he asked me if Einstein was just doing philosophy
before special relativity was proved and if he was just doing
philosophy before general relativity was proved. My cousin says that
Einstein's idea that the universe is 4 dimensional all there at once
is really physics and not philosophy because the world tubes and
slices are predicted by the mathematics. But I did not like the
arguing and Frank and my cousin getting angry so I will not cause
any anger like that here and ask any more questions here.

I printed out my spacetime picture that I did here and told him
about making a symetric one so he added on another moving world tube
going in the opposite direction and showed me that each mover saw
the other's world tube slice to be shorter than his own and that
each one saw an earlier time on the other one's world tube. So I
went back to my room and made it up for my last post here. I played
like my cousin is moving away from me to the right and Frank is moving
away from me to the left at the same speed.

 

[PeterDonis]

he asked me if Einstein was just doing philosophy
before special relativity was proved and if he was just doing
philosophy before general relativity was proved.

Just to be clear, nobody here has been saying that SR or GR are just philosophy. We have only been saying that the "block universe" or "ether theory" *interpretations* are just philosophy. SR and GR are certainly scientific theories; they make plenty of predictions about experimental results, and those predictions have been verified, in some cases to ten or more decimal places.

My cousin says that
Einstein's idea that the universe is 4 dimensional all there at once
is really physics and not philosophy because the world tubes and
slices are predicted by the mathematics.

The world tubes and slices are indeed there in the mathematics, but they by themselves don' t prove that "the universe is 4 dimensional all there at once". That's a much stronger claim.

 

[Dale]

My cousin says that
Einstein's idea that the universe is 4 dimensional all there at once
is really physics and not philosophy because the world tubes and
slices are predicted by the mathematics.

The thing that I like about math is that there is generally more than one way to write the same thing, and due to the logical framework of math itself, you are guaranteed that both ways of writing are logically equivalent. So, if the world is 3D evolving in time then we would write the position of a particle as follows:
$(x(t),y(t),z(t))$

But we are always free to replace $t$ with some function $t(λ)$, and we can write $x(\lambda)=x(t(\lambda))$. So now we can write a completely equivalent expression for the position of a particle like this:
$(t(\lambda),x(\lambda),y(\lambda),z(\lambda))$

This last expression is what we would write if the world is 4D. So, mathematically, the 3D and 4D worlds are completely equivalent and you can always mathematically rewrite any expression from one form to the other. It seems intuitively like there should be some phenomenal difference between the two, but there isn't. Logically (rather than intuitively), a 3D time evolving world is completely equivalent to a 4D world.

 

[TheBC]

Yes. And SR, as a theory, is the Lorentz transform (with its experimental interpretation).

For some reason you keep trying to equate SR with the block universe interpretation, but the block universe is outside the theory and is only an interpretation.

I don't think Einstein considered it outside his theory.That's why he 'interpreted' his own theory without an ether, and as follows:

From a "happening" in three-dimensional space, physics becomes, as it were, an "existence" in the four-dimensional "world". >> Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's Four-Dimensional Space ("World") (supplementary to section 17 - last section of part 1 - Minkowski's Four-Dimensional Space).

<< Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> Albert Einstein, "Relativity", 1952.

What Poppers says about his encounter with Einstein is also interesting:

<< The main topic of our conversation was indeterminism. I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. (He agreed that this had been his view, and while discussing it I called him "Parmenides".)... >> Karl Popper, Unended Quest: An Intellectual Autobiography.Routledge Classics. Routledge. pp.148–150.

Based on above quotes it is -in my opinion- extremely difficult to refute that Einstein's 'phyilosophical' 'interpretation' is block universe, and not ether.(Irrellevant of the fact whether we have to agree ether is another valid 'interpretation').

Then, if they are different theories, please provide one experiment which could, in principle, distinguish between the two.

If the answer is no, then LET = SR. Which is obviously false.
It's not because they use the same LT ,that LET = SR. Why? Because they include different explanations (dynamical vs kinematical).

We probably have different views on what science and theory is all about. In dealing with SR I prefer therefore to stick to what Einstein says about his own SR, and that does not include ether. In SR the ether is -quote Einstein 1905- 'superfluous'.

 

[Dale]

Based on above quotes it is -in my opinion- extremely difficult to refute that Einstein's 'phyilosophical' 'interpretation' is block universe, and not ether.(Irrellevant of the fact whether we have to agree ether is another valid 'interpretation').

Nobody is attempting to refute that. The block universe was clearly Einstein's preferred philosophical interpretation. It is also my preferred interpretation.

If the answer is no, then LET = SR. Which is obviously false.
It's not because they use the same LT ,that LET = SR. Why? Because they include different explanations (dynamical vs kinematical).

I note that you, like all your predecessors, are unable to provide any experiment to distinguish between LET and the block universe interpretations. Thus you demonstrate, yet again, that they are two different interpretations of the same theory rather than different theories.

Also, I appreciate how you highlight at the end that the only difference is the explanations, as we would expect for interpretations of the same theory.

 

[bobc2]

LET and PF Rules

Thus you demonstrate, yet again, that they are two different interpretations of the same theory rather than different theories.

I don't see why you keep bringing up LET when the forum Rules have explicitly identified this as a discredited or superced theory. You are prohibited from continually advancing LET on PF. Here is Greg's statement again, which was called to our attention in an earlier post on this thread.

The PF Rule: "Generally, in the forums we do not allow the following:

Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory)."

 

[Dale]

I don't promote LET. It is merely a counterexample to the claim that the block universe is uniquely implied by the Lorentz transform.

In fact, when people have come here to promote LET, I have consistently argued against them. I consistently oppose the promotion of any philosophical viewpoint here.