Do we live in 3 or 4 dimensions?

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Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory);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

 

[TheBC]

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

Sorry, you are maybe not aware of it, but you DO promote LET by the simple fact stating it's a valid counterexample. If ether/LET has been discredited or superseded, then it should not be used as a valid alternative to Block Universe. According to the rules you may still only use it in an historical context.
I will not repeat Einstein's quotes once more, but Einstein himself never interpreted his SR/LT with an ether. On the contrary.
Or would you consider this spreading misinformation?

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.

If you consider any interpretation of numbers plain philosophy. But is this what physics is about?

Great sketch, Bobc2.

 

[Fredrik]

Sorry, you are maybe not aware of it, but you DO promote LET by the simple fact stating it's a valid counterexample. If ether/LET has been discredited or superseded, then it should not be used as a valid alternative to Block Universe. According to the rules you may still only use it in an historical context.

How many times do we have to explain this? LET is a theory that was replaced by SR, because SR is more elegant and doesn't require an ether. LET doesn't have a block universe interpretation, because it mentions the ether in its definition. SR on the other hand, has two interpretations: The block universe interpretation and the ether interpretation. The former is simple and elegant. The latter is complicated and weird.

LET is no longer used because it forces the ether interpretation upon us. SR is preferred because it doesn't.

To "promote LET" would be to say either that SR is wrong and the original LET is right, or that the ether interpretation is the only correct interpretation of SR. To admit that SR has an ether interpretation is not to resurrect a dead theory. It's just a statement of a fact.