Page 1 of 6

### Why is relativity so hard to learn?[1]

Posted: April 25th, 2017, 11:34 am
Judging by the number of threads in Physics and Personal Theories asking questions (or proposing theories) about it, relativity is hard to fathom for beginners. This was also my own experience when, already an experienced engineer, I started to question relativity for the first time.

I do not want to make this a Blog of my personal (uncompleted) journey towards understanding relativity, but there are certain key insights that stand out, which I will discuss briefly. Perhaps it will stimulate others to tell their own tales of learning relativity, be it successes or failures. Perhaps we can all learn why popularizations generally failed and maybe together we can come up with some better scheme for introducing/teaching relativity.

After years of battling with Special Relativity (SR), reading every popular book that I could lay my hands on, I stumbled upon Nigel Calder's "Einstein's Universe, the layman's guide" (Penguin Science, 1979). It is a piece of well-written popular science, so it does give some insight, but it did not give me 'real answers'. I still did not understand relativity when I finished the book, but one thing jumped at me: he started the book with General Relativity (GR) and only later showed that it reduces to SR when gravity is weak. If I remember correctly, his rationale was: if you start with SR, everything is too "footloose", while starting with GR, you can have your feet planted firmly on the ground. How cool is that?

So I started to look at the math of GR, but what a shock - the good stuff was way over my head! To make a long story short, once I (partially) coped with the tensor math, I translated it back into more engineering-like math. With that I could eventually do the calculations for reasonably 'simple' scenarios, like free-falls and orbits near a black hole. This sparked me on to also tackle cosmology and I found it to be pretty simple, once you got the hang of GR. In fact I think at that stage I understood contemporary cosmology better than I understood SR.

It took me quite some time to figure out how SR fits into the whole scheme of things. I found the secret to be that for any inertial observer, in his immediate vicinity (whether in a gravitational field or not), space is isotropic, the same in all directions. From this stems all the standard stuff of SR: like that the observed speed of light is the same for all inertial observers; that their definitions of simultaneity are different (but calculable); that there is a spacetime interval that must be the same for all inertial observers; why the 'twin-paradox' is not a paradox, and so on...

And finally, it helped me understand that proper acceleration (like what you would feel in a rocket blasting through space) gradually defines a new spacetime structure for a temporarily accelerated (but later inertial) observer. Such a difference in spacetime structure causes different inertial observers to record different distances and elapsed times between the same two events. It does not mean that their yardsticks (of space and time) are necessarily different - they just go through non-equivalent paths in spacetime. Most misunderstandings of relativity are rooted in these principles.

In order not to make this post overly long, I will leave it here and invite opinions on the main topic, before going deeper into what the isotropy of space, spacetime structure, and their visualization aids might mean. And in a non-math fashion, if at all possible.

### Re: Why is relativity so hard to learn?

Posted: April 25th, 2017, 3:33 pm
I studied SR from a variety of texts but most recently by Bernard Schutz. Though I also had a professor's treatment in handouts that did a very good job presenting the subject in terms of 4 dimensional vectors.

I had the most success studying GR from Robert Wald. I also tried Hawking's "Large Scale Structure of space time" but the math was a bit abstract and thick so I cannot recommend it.

I used what I learned in both to make a relativity space flight simulator called relspace. It shows what you see as a result of the aberration of light or if you filter this out then you see the lorentz contraction. It also shows what happens to light near a black hole. Though this is only visible in map mode because actual encounters with a black hole are quite difficult for a number of reasons and the basis for my claim that, "if you actually see a black hole then it is way too late for you!" Near enough to see the schwartschild radius, the gravity is just too strong that you end up whipping by the things in too short of a time to even see the thing. So what you will most likely be able to see are the accretion disk and the jets.

The idea that one should start with GR rather than SR is bizarre in the extreme to me. SR is basic to so many subjects and the mathematics is simple algebra. However, as I mentioned before, using the Lorentz transformations is rather tricky, for just plugging any old numbers can give results which are hard to understand. It is a struggle every time I use them but with a lot of practice you get used to it.

### Re: Why is relativity so hard to learn?

Posted: April 25th, 2017, 5:17 pm
Nigel Calder! "Timescale". For a moment you had me thinking "Now there is a man whose writings I can understand." I was ready to go for it until you (Burt) said "I still did not understand relativity when I finished the book," Oh, dear. Truth to tell, though, I don't think it's so much that I do not understand it as that I do not believe much of it. Can those be the same thing?

### Re: Why is relativity so hard to learn?

Posted: April 25th, 2017, 11:48 pm
BurtJordaan » April 25th, 2017, 9:34 am wrote:And in a non-math fashion, if at all possible.

Perhaps that's the source of the difficulty.

People want a qualitative or intuitive grasp of a subject that is inherently mathematical. Any qualitative explanation of relativity is not relativity itself.

Classical physics is the same. What is Newtonian gravity without math? "Matter attracts other matter." You can't do any better than that. To understand Newton's theory of gravity you must say, "Matter attracts other matter with a force equal to the product of their masses divided by the square of the distance between their centers, all of that times a constant." Or in the compact math notation, $F = G \frac{m_1 m_2}{r^2}$.

There is philosophical significance to this. Modern physics -- that is, our best theories about the nature of the world -- can not be understood without advanced math. And math is hard. Differential geometry, the math behind relativity, is an upper division or graduate level course for math majors. Tensor calculus and lots of it.

What does it mean that our very understanding of the world depends on being able to work with advanced math? Isn't that unfair to everyone else? Are the poets and artists not allowed to know how the world works? Why is that?

These are important questions.

We know from quantum theory that sometimes the ONLY thing you have is the math, and everyone argues about the intuitive meaning of the equations. Now that's mysterious!!

But that's the essence of the problem. Physics is inherently mathematical. Intuitive or qualitative explanations are bound to be insufficient.

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 8:57 am
vivian maxine » 25 Apr 2017, 23:17 wrote:Truth to tell, though, I don't think it's so much that I do not understand it as that I do not believe much of it. Can those be the same thing?

Maybe. People that understand it mostly believe relativity, not because it is dogma, but because experiments support it. Understanding the theory to some degree makes it a lot easier to understand the experiments.

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 9:27 am
mitchellmckain » 25 Apr 2017, 21:33 wrote:The idea that one should start with GR rather than SR is bizarre in the extreme to me. SR is basic to so many subjects and the mathematics is simple algebra.

The problem as I see it, is that the present system may work for formal students, but it apparently has a very low yield for the informal student. The majority of our members seem to (relativistically) belong to the latter group.

Is there a better way for them?

### Re: Why is relativity so hard to learn?[2]

Posted: April 26th, 2017, 1:00 pm
BurtJordaan » 25 Apr 2017, 17:34 wrote:I will leave it here and invite opinions on the main topic, before going deeper into what the isotropy of space, spacetime structure, and their visualization aids might mean.

OK, I will now attempt to describe the isotropy of space. I think most newcomers to science will agree that if you would be inside a large cubical, windowless and non-rotating laboratory, which is floating weightlessly somewhere is space, you will not be able to tell which way is up, down, east, west, north or south for the laboratory as a whole. But, you can obviously mark one end as the ceiling, the opposite end as the floor, another side as the east wall, the opposite side as the west wall, and so on, according to your free choice.

Essentially, you have set up a 3-dimensional inertial reference frame for your lab's internal space (not spacetime, yet). You may not know where you are in space at large, but if you are strapped to the exact center of the lab, you surely know where you are relative to the lab. You can decide to label that center point x=0, y=0, z=0. I think all would agree that the internal space is isotropic, i.e. without any other markings, all directions will look the same. If you use a handheld laser distance measuring device, the distance from you to the center of each of the six sides will be exactly the same. The same for the distance to each of the eight corners of the lab.

Now let us say your lab has a rocket attached to the outside of your chosen 'floor' and it is ignited for some time, pushing the lab in the direction of your ceiling. You will feel something like gravity working towards the floor. If you repeat exactly the same laser distance measurements as before, you will find that according to the device, the floor is slightly closer to you than it was before and that the ceiling is slightly farther away than before.

The floor and ceiling situation is quite obvious, because while the laser light was propagating from you to the floor, the floor came a little closer due to the push of the rocket, while the opposite has happened to the ceiling. In fact the distances to the other four sides will all come out slightly larger than what they were before, but let us ignore that for now. We will come back to it later in this thread.

While the rocket is burning, you can clearly feel (and measure) which way is up, which way is down and which are the 'sideways' directions, in the conventional down-to-earth sense. Without any numbers to work with, the only thing that you can conclude is that space inside your lab is no longer isotropic, but that space is somehow different in the direction of the floor than it is in the direction of the ceiling - and that both are different from the space in the 'sideways' directions. We will define the differences better later.

Now let us stop the rocket's burn, so that you become weightless again. Repeat the same laser experiment and you should not be surprised to find that the isotropy of the space inside the lab has been restored. All six sides will again be at exactly the same distance from you than what they were before the rocket blast. This is the essence of the isotropy of space. There is more to it, but for now, this is nothing new. Einstein, Newton and Galileo would all have agreed with us. Or would they?

I will leave with this question for now. What do you think?

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 1:13 pm
BurtJordaan » April 26th, 2017, 7:57 am wrote:
vivian maxine » 25 Apr 2017, 23:17 wrote:Truth to tell, though, I don't think it's so much that I do not understand it as that I do not believe much of it. Can those be the same thing?

Maybe. People that understand it mostly believe relativity, not because it is dogma, but because experiments support it. Understanding the theory to some degree makes it a lot easier to understand the experiments.

The first I ever read of it was a book by Carl Sagan. I understood it quite well. Then I began to hear these (to me) unbelievable stories and I've had it on the high shelf ever since. Shall be interesting to follow your explanations.

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 2:01 pm
Hi Jorrie,

Not bad. Let's give us some relative coordinates inside this lab. Let's say the Lab is square at 20 meters per side. Located in the center of such a Lab, would put us at +/- 10 meters to all closest surfaces.

We can accept that the Lab has Air for us to breath and is sealed from the Vacuum of Space outside.

We can accept that the Atmosphere inside the Lab is carried within the Lab.

Are we to accept that the Physical Space inside the Lab is also carried and sealed within the Lab like the Atmosphere? Or is the Lab moving through a Continuum that permeates and passes through the Lab?

I might suggest that a better Model would describe Space as being a very very very fine Atmosphere.

The walls are like course mesh screens. The walls serve the purpose of keeping such course objects such as the Air we breath contained within the Lab, but the fine Atmosphere of Space is so fine as to pass right through all walls, including us occupants. It's so fine we don't even feel it as we might feel a wind. It blows right though us too.

Not exactly the ideal Model, but provides a better foundation to understand what comes next. IMHO..

Regards,
Dave :^)

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 2:14 pm
Not a bad model, Dave, but what answer to the question in my prior post will the theory spit out?

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 3:17 pm
Hi Jorrie,

Not sure what is meant by: "what answer to the question in my prior post will the theory spit out?"

I assume the question is in regards to the statement: "Einstein, Newton and Galileo would all have agreed with us. Or would they?"

I'm not sure Galileo had a working hypothesis regarding "Space". But Newton believed "Space" was a continuum, like a fine atmosphere. Unfortunately, because we couldn't measure our speed through such a continuum, the Aether continuum lost face and was abandoned. Einstein revived the continuum concept with General Relativity but chose to call it by a different name (Space-Time).

Anyway, I believe it important to understand Relativity, that it is equally important to understand the existence of this continuum, because it has so many profound effects on everything that moves through it, or should I say "as it moves though you".. (it being mostly stationary and you (or Lab) being the actual mover.. lol).

Again, this is not my preferred Model, but my Model is a bit too abstract to have a place here. Also, not my intent to distract or object to any aspect of Relativity. I fully endorse it. My only deviation has to do with absolutism and I won't bring that up in this thread (again.. lol).

So we have a Lab in a flat even Space Continuum (no outside gravity). When the Lab is NOT being accelerated, the continuum blowing through us is steady and consistent (isotropic).

Anyway, I'm hoping to learn something here too (Ie: Time), so please continue Jorrie.

Best Regards,
Dave :^)

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 3:32 pm
BurtJordaan » April 26th, 2017, 8:27 am wrote:
mitchellmckain » 25 Apr 2017, 21:33 wrote:The idea that one should start with GR rather than SR is bizarre in the extreme to me. SR is basic to so many subjects and the mathematics is simple algebra.

The problem as I see it, is that the present system may work for formal students, but it apparently has a very low yield for the informal student. The majority of our members seem to (relativistically) belong to the latter group.

Is there a better way for them?

Actually it is not much difference because many of the more difficult subjects leave students largely on their own. Classes are rarely taught on the subjects. For example, I went through Robert Wald (GR) completely by myself working through all the derivations. Even SR is something where I learned more from my independent studies than in the classroom. The biggest advantage for the formal student is more to do with preparation and practice with both study methods and research.

Of course that probably depends a great deal on the school. That may be different in the more expensive science focused schools, but that is the way it was at the University of Utah where I studied.

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 11:24 pm
someguy1 » 26 Apr 2017, 05:48 wrote:
BurtJordaan » April 25th, 2017, 9:34 am wrote:And in a non-math fashion, if at all possible.

But that's the essence of the problem. Physics is inherently mathematical. Intuitive or qualitative explanations are bound to be insufficient.

Right, but everyone tries to connect people's intuition to the observed reality. I am striving for a community effort here to try and narrow the (apparently large) gap.

### Re: Why is relativity so hard to learn?

Posted: April 26th, 2017, 11:30 pm
Dave_Oblad » 26 Apr 2017, 21:17 wrote:So we have a Lab in a flat even Space Continuum (no outside gravity). When the Lab is NOT being accelerated, the continuum blowing through us is steady and consistent (isotropic).

Hi Dave, from the above, can I assume that you reckon the "continuum blowing through us ... steady and consistent (isotropic)" is not detectable? That we cannot know how fast it is blowing through us or in which direction? That its 'blowing through' does not change the path of light beams, or the laser distance measurement in any direction?

### Re: Why is relativity so hard to learn?

Posted: April 27th, 2017, 7:24 am
someguy1 » April 25th, 2017, 10:48 pm wrote:
BurtJordaan » April 25th, 2017, 9:34 am wrote:And in a non-math fashion, if at all possible.

Perhaps that's the source of the difficulty.

People want a qualitative or intuitive grasp of a subject that is inherently mathematical. Any qualitative explanation of relativity is not relativity itself.

Classical physics is the same. What is Newtonian gravity without math? "Matter attracts other matter." You can't do any better than that. To understand Newton's theory of gravity you must say, "Matter attracts other matter with a force equal to the product of their masses divided by the square of the distance between their centers, all of that times a constant." Or in the compact math notation, $F = G \frac{m_1 m_2}{r^2}$.

There is philosophical significance to this. Modern physics -- that is, our best theories about the nature of the world -- can not be understood without advanced math. And math is hard. Differential geometry, the math behind relativity, is an upper division or graduate level course for math majors. Tensor calculus and lots of it.

What does it mean that our very understanding of the world depends on being able to work with advanced math? Isn't that unfair to everyone else? Are the poets and artists not allowed to know how the world works? Why is that?

These are important questions.

We know from quantum theory that sometimes the ONLY thing you have is the math, and everyone argues about the intuitive meaning of the equations. Now that's mysterious!!

But that's the essence of the problem. Physics is inherently mathematical. Intuitive or qualitative explanations are bound to be insufficient.

someguy, only a highly-educated-in-math professional would make such statements. Your position is great for those who already understand upper math in all it's stages. My bets are on Burt when it comes to educating the non-mathematician who only wants to know what it is all about. As Burt said, "And in a non-math fashion, if at all possible."

I remember to this day how her eyes lit up when I managed to explain fractions to a very panicked student using no math at all. I imagine that is hard for a fully-educated mathematician to understand, maybe because it is hard to mentally step back to sixth grade. But I assure you the basic concept of things can be taught to the laity without math.

Of course, if someone in that laity really wants more understanding, then they can ask more and find more, even on their own. But I don't think that was Burt's goal, was it?

### Re: Why is relativity so hard to learn?

Posted: April 27th, 2017, 1:53 pm
Hi Jorrie,

Jorrie wrote:Hi Dave, from the above, can I assume that you reckon the "continuum blowing through us ... steady and consistent (isotropic)" is not detectable? That we cannot know how fast it is blowing through us or in which direction? That its 'blowing through' does not change the path of light beams, or the laser distance measurement in any direction?

I will agree that we can't measure any change.

But for those interested in a bit of detail, there is this effect called the "Aberration of Light". When we shoot a photon from our Laser expecting to hit one of the side walls while we have a non-accelerating velocity in the direction of the ceiling of the lab from the previous acceleration mentioned (now we are coasting upwards), the photon will take time to travel from the Laser to the far center of the wall. We have a velocity coasting upwards (like an elevator rising), so this "Space Wind" is in essence blowing downwards through us.

Now, since we are aiming directly at the center of any far wall and shooting from the center of the room, one might expect that in the time it takes for a Photon to leave the Laser and reach the Center of the far wall, that we have moved a bit further upwards in that time and intuition would have us expect to hit the far wall a tiny bit closer to the floor. For example, if one want's to shoot a skeet, one aims in front of the moving skeet so your bullet intercepts the skeet. If you aim directly at the skeet, it won't be there by the time your bullet gets to the skeet.. right?

Not so with Light! If you want to hit the center of the wall with a Photon Bullet from your Laser, you aim exactly where you want to hit, in this case.. dead center of a far wall. So why don't we have to lead the target like if we where shooting a skeet? The "Aberration of Light" is why. This "Space Wind" has an effect on the path of the Photon Bullet, that causes the path to automatically "lead" the Target by an exact amount and "Zonks!" (that's a technical term.. lol) you hit the wall exactly where you were aiming.

If the far wall dead center had a Mirror and it bounced that Photon bullet back towards you, again this "Space Wind" has the same effect causing the bounce path to lead (upwards) and Zonks again, the Photon goes directly back into the barrel of the Laser Gun.

This "Aberration of Light" is just one of the fun things that the Universe throws at us that Hides our Motion through it, making it impossible to measure our velocity through this Space Wind.

Ok, hope that wasn't too much detail.. pretty simple actually.

Best wishes,
Dave :^)

### Re: Why is relativity so hard to learn?

Posted: April 27th, 2017, 3:51 pm
Even SR is something where I learned more from my independent studies than in the classroom.

Yes. Academia is all about ramming the procedures into you so you can take a midterm exam. They don't cover the history of the development of the subject. For the history you get is a couple short paragraphs and some sidebar notes in the textbook.

The history of Special Relativity involved lots of players on the stage other than Einstein. Hendrik Lorentz and Hermann Minkowski stand out prominently.

The early development of SR was actually extrapolating on electromagnetism as given by Maxwell's Equations. Maxwells equations are sine-qua-non for electromagnetism in physics. Well ... they are if all the magnets and wires involved are bolted to the laboratory desk. If you start moving around with magnets on moving platforms, and maybe even someone with a battery is moving along with said platform, Maxwell's equations break down.. and break down hard. This dirty secret is what Lorentz knew about, and where he enters stage left into this drama.

Additional evidence that this was initially about electromagnetism can be found in the title of one of Einstein's 1905 publications. "Zur Elektrodynamik bewegter Körper", literally "On the Electrodynamics of Moving Bodies"

Claim: {Einstein said that energy and mass are the same thing.} Really? Did he ever really say that? Actually in another paper from 1905, Einstein found something that implies mass-energy equivalence, but described it right from the beginning as "a very interesting result" (einer sehr interessanten Folgerung) of his earlier calculations. Seemingly to indicate to the reader that he was personally surprised by this particular prediction of the equations.

The actual paper in that instance showed that if a black body emits radiation, its mass decreases. E=mc2 is hiding unnoticed among the paper. The equation was written in earnest later by another physicist. Again indicating that SR had many players on its stage.

All these quandaries and debates about whether fields are dragged along with the charged bodies that create them. Whether space exists or merely relative locations of objects. Whether the aether is the medium of propagation. Whether said aether is 'dragged' along with the earth. (so-called Aether Drag Theories)

All these debates were voiced loudly and raged at the time. Tensions ran deep. Furniture was broken. Friendships were ended. At the center of this drama was the very nature of space and time. Every countervailing idea was voiced and re-hashed to death. What Einstein produced was a theory that contained no aether at all, fully covariant, and mathematically consistent. The only remaining question was whether our universe acts that way or not.

When the dust settled, there was only one man left standing : Einstein and his theory.

### Re: Why is relativity so hard to learn?

Posted: April 27th, 2017, 3:55 pm
Dave_Oblad » 27 Apr 2017, 19:53 wrote:Ok, hope that wasn't too much detail.. pretty simple actually.

Actually Dave, far too much detail, because the relativity explanation is simpler by far! ;-)

What you have described is views from two different inertial frames. In relativity we only need to consider the inertial frame where the shooter and the target is at rest relative to each other. Then the laser always hits exactly where you aim. No "space wind" or other spooky aberrations to consider. Even in the presence of mild gravity, you still aim exactly at where you see the target (provided that the 'bullet' is a photon, of course).

### Re: Why is relativity so hard to learn?[3]

Posted: April 27th, 2017, 4:16 pm
BurtJordaan » 26 Apr 2017, 19:00 wrote:Now let us stop the rocket's burn, so that you become weightless again. Repeat the same laser experiment and you should not be surprised to find that the isotropy of the space inside the lab has been restored. All six sides will again be at exactly the same distance from you than what they were before the rocket blast. This is the essence of the isotropy of space. There is more to it, but for now, this is nothing new. Einstein, Newton and Galileo would all have agreed with us. Or would they?

Interestingly, Galileo and Einstein would have agreed with us,[1] but Newton would not have agreed. He would have argued (if laser distance measuring equipment were available in his time) that the laser distance measurements to the ceiling and the floor after the acceleration would have been larger than before the acceleration. He would have said the same for the laser-distances from the center to the walls, but crucially, he would have calculated that the wall distances would not have increased by as much as the ceiling and floor distances.[2] In other words, the former cubical lab would now appear to be stretched lengthwise.

The reason for this is that Newton postulated an absolute space and a universal time and that light moves through this absolute space (aether) at a constant speed, as measured against the universal time. Since the acceleration must have changed the speed of the lab against the absolute space, the speed of light can no longer be isotropic and the laser distance meter can no longer measure distances correctly. OK, Newton would probably have just said that unless we know the speed of the lab against his absolute space and then correct for that, light is not useful for distance measurements.

The problem that Newton would have faced, if he has lived today, is that we can do such experiments. Not exactly as described (laser rangefinder measurements are not quite accurate enough at the speeds that we can achieve), but we could have used a Michelson interferometer[2] in our lab. This would not have shown any anisotropy in the propagation of light. We would have found no change, neither before, nor after the period of acceleration, a fact which contradicts the Newtonian prediction.

Einstein abolished the absolute space idea and simply predicted the isotropy of space from the point of view of any inertial frame. Together with absolute space, Einstein also abolished physical length contraction, as proposed by Lorentz to explain the interferometer experiment. Everything that Einstein predicted was eventually verified as correct by experiments, including the outcome of the so called twin-"paradox".

We have seen that during the acceleration, the space observed with the laser rangefinder was not isotropic. The distances to floor and ceiling did not remain the same, but assumed some different values. So how did isotropy 'magically' return after the acceleration stopped? In order to understand that, we must turn to the spacetime structure - not to time (yet), because we did not really use time in the interferometer experiment. Spacetime structure will be topic of the next part.

Notes:

[1] As Dave_Oblad hinted, Galileo never directly wrote anything about absolute space. He just stated that the laws of motion are the same in all inertial frames, which was later interpreted as "Newton's laws of motion are the same in all inertial frames". For details, see: https://en.wikipedia.org/wiki/Galilean_invariance.

[2] For a more technical discussion, see https://en.wikipedia.org/wiki/Michelson and also: Observer_comoving_with_the_interferometer.

### Re: Why is relativity so hard to learn?

Posted: April 28th, 2017, 6:20 am
Hi Everyone,

You are going to hear a lot about FRAMES. I would like to remove most of that mystery right now.

First, I'll give an argument I presented long ago that sounds perfectly logical. Then I'll explain why I was wrong.. Hint: It's about FRAMES.. lol.

See, we all know Light has a speed limit.. right? It's about 186,000 Miles Per Second or in metric it's about 300,000 Kilometers Per Second. So, if I put a Mirror about 300,000 Km away from me and shot a Laser Flash at the mirror, the round trip time from my Laser Gun to the Mirror and Back would be about 2 seconds for a total distance traveled of 600,000 Km for my Photon Bullet. That's pretty freaking fast.. but it is not instantaneous.

So I had this idea: What if I had a Spaceship and my friend had an identical Spaceship. Suppose my friends Spaceship was 300,000 Km away from me. Suppose both of us are moving real fast in the exact same direction while always keeping the exact same 300,000 Km distance between us. Let's also imagine both of us are going about 1/2 the speed of light, of course, maintaining this parallel course with each other.

So I ask myself: If I had a telescope and looked out my window at my friends Spaceship.. will it look like it is even with me or behind me? Think about that. It takes 1 whole second for the light from my friends Spaceship to reach me. I reasoned that even if I knew for a fact it was even with me, the time delay for the light to get from there to here would mean I should be seeing where it was 1 second ago. So Logically, it should look like I'm ahead of my friends Spaceship.. right?

I also reasoned that if I wanted to shoot a Laser Beam at it, I should probably not shoot straight at it, because I Know it's really up even with me. I also reasoned that to hit my friends ship, I should shoot way ahead of it so by the time my Laser shot reached my friends Ship, they would intercept at the same time and place.. right? Like shooting a skeet, you should have to shoot ahead of your target so your bullet and skeet arrive at the same time and place to score a hit.. logical right?

Wrong!

Remember that "Aberration of Light" thing I mentioned earlier? What happens is the light coming from my friends ship is not going to come straight at me. The Space Wind is going to change the angle of the light and create an interesting effect. It will look like my friends ship is dead even with me, which it actually is and not 1 second behind me as I had logically deduced I should observe. Further more, should I wish to shoot it with my Laser Gun.. do I shoot straight at it or shoot ahead of it.. like leading my target so my beam and that Ship will intercept 1 second later? If you guessed you shoot straight at it, you would be correct (yea). Because that "Aberration of Light" thing will change the angle of my Beam to automatically lead my Target and, Zonks again, I hit it exactly where I was aiming. How sweet is that?

This is why I felt it important to realize this Space Wind is real, because it has profound effects on Matter and Energy.

So what has this to do with Frames? My Ship and that other Ship are coasting at exactly the same speed. Light angles are aberrated such that we look even with each other. My Ship and my Friends Ship are said to share the same Frame! It's called an Inertial Frame because we are both Coasting. It's a Shared Frame because we are both coasting at the Exact Same Speed. The Space Wind is the same for both of us.

So, besides changing Light Angles, what else does this Space Wind do to us? Well, for one thing it slows down our Clocks. The faster we go, the faster this Wind blows through us, the slower our Clocks run. And not just our clocks, but all our clocks, including our Biological Clocks. That's right.. the faster we go, the slower we age. So if you were on a Spaceship and going super fast, like 99% the Speed of Light, a journey that might take 100 years (for those poor slobs we left at home on Earth) would only seem like about a few weeks to us travelers. That's super cool.

The downside of aging so slowly is that all your friends you left back home will be long dead by the time you reach your destination, even if it only measured a few weeks by your wrist watch. But another upside is you don't have to pack enough food to last 100 years, just a few weeks would be enough.

Now that my point is made, don't start packing your bags yet. It takes a long time to get going that fast and a lot of fuel and/or power to get up to such high speeds.. so we still have a lot of problems to solve before we can travel to the Stars.

Anyway, once you get the idea that aging and clocks are slowed down by raw high speed, we have some additional bits of information to swallow. Like.. what if I, in my Ship, are traveling faster than my friends Ship? Obviously.. we won't be sharing that same FRAME anymore. If I'm going faster.. then my clocks will be running slower than the clocks in my friends Ship. I will be aging slower than my Friend too.

That's where Relativity comes in. The Math Einstein published (Special Relativity and General Relativity) allows us to calculate how each unique Traveler, each within their own Speed Frame, would know how fast (or slow) each others clocks are running.. from everyone's unique points of View.

So, you will be hearing the term "FRAME" a lot in talks about Relativity. The Lab we started talking about above has its own unique Frame. Another Lab, if traveling at the Same Speed, could be referred to as sharing the Same Frame, even if they are very distant from each other. An Inertial Frame is just a Frame that is coasting at whatever speed. Obviously, a Non-Inertial Frame is one that is changing speed and gets a lot more complicated when doing Frame comparisons.

Basic Relativity usually just compares coasting Frames (Inertial Frames). This "Wind" I keep referring to was called the "Fabric of Space-Time". The "Space" part is obvious because different Frames are separated by Space but the "Time" part is because our Speed through "Space-Time" affects our measurements of "Time".. as in.. the faster we go.. the slower we age and of course the slower our clocks run.

The Math can get complicated but the ideas.. are really pretty simple. If we can get our Lab up to about 86% the Speed of Light, our clocks will be running 50% slower within this Frame. But to you, also inside this Lab Frame, the clock on your wrist will seem to be running at a normal rate, because you are also slowed down. Everything will seem perfectly normal inside your personal Lab Frame.

I'll call this Relativity for Dummies (like me.. lol). I ain't had much book learnin. And hopefully, this over simplified Model hasn't made it more difficult for Jorrie to get some of the finer points across. It's not my intention to be misleading through over simplification.

The Universe seems to Conspire to hide our Speed through it from us. Isn't that just ducky ;)

(Jorrie told me that once.. minus the ducky part.. lol)

Best wishes,
Dave :^)

### Re: Under Arrest

Posted: April 28th, 2017, 9:44 am
Hi Dave,

As you describe it, the two ships on parallel paths are at rest with respect to each other. End of discussion!

You can say they're moving or not* wtr to some other reference frame but they each share the same one. They're like two opposite walls of Jorrie's mobile lab. I don't see the need for "space wind".

*because you're free to declare that "other frame" to be the one that's "moving".

### Re: Why is relativity so hard to learn?

Posted: April 28th, 2017, 1:23 pm

I throw in the Space Wind, because we should have a reason <why> clocks slow down. Without a Space Wind, clocks would not know <how much> to slow down. All clocks would run at the same rate (regardless of speed) and we would not have a reason to have FRAMES. Without our Space Wind, we wouldn't have the Aberration of Light.

Again, this "Space Wind" is just a continuum that Einstein called the Fabric of "Space-Time" and now we should probably start calling it by that correct name. The term "Space Wind" has served its purpose. We can't block it from being part of us and blowing right through us as we move through it.

If we could block it, we could have a way to block Gravity. That would be cool if we could figure out a way. I'd love to float around my house when I wanted.

Regards,
Dave :^)

### Re: Why is relativity so hard to learn?

Posted: April 28th, 2017, 3:09 pm
hyksos » April 27th, 2017, 3:51 pm wrote:

The early development of SR was actually extrapolating on electromagnetism as given by Maxwell's Equations. Maxwells equations are sine-qua-non for electromagnetism in physics. Well ... they are if all the magnets and wires involved are bolted to the laboratory desk. If you start moving around with magnets on moving platforms, and maybe even someone with a battery is moving along with said platform, Maxwell's equations break down.. and break down hard. This dirty secret is what Lorentz knew about, and where he enters stage left into this drama.

I have heard this but am finding it hard to find it discussed anywhere. You wouldn't have a link ,would you where this particular point is fleshed out?

I am also interested to know if the invariabilty of the spacetime interval applies only to inertial frames of reference or whether (as believe ) it applies to all frames of reference-including accelerating ones.

As to the OP I have learned nearly all that I know of GR from forums such as this supplemented with reading around the subject in a loose way.

I do find it counter intuitive and extremely hard but am prepared to accept that this is just normal.(sadly my mathematical abilities are too weak "to take up the slack" but I can live with this)

### Re: Why is relativity so hard to learn?

Posted: April 28th, 2017, 5:38 pm
jocular wrote:As to the OP I have learned nearly all that I know of GR from forums such as this supplemented with reading around the subject in a loose way.

I wish I could say the same. If what has followed is about relativity, I am lost. But I suppose that is to be expected. I shall carry on.

### Re: Why is relativity so hard to learn?

Posted: April 28th, 2017, 8:04 pm
Hi all,

As to the subject of my Space-Wind, we can call it Space-Time, Aether or even a Field.

Hyksos wrote: What Einstein produced was a theory that contained no Aether at all, fully covariant, and mathematically consistent. The only remaining question was whether our universe acts that way or not.

This would be true for Special Relativity. But that was replaced with General Relativity with Space-Time as an alternate Aether.

Robert B. Laughlin, Nobel Laureate in Physics, endowed chair in physics, Stanford University, had this to say about ether in contemporary theoretical physics:

It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed [..] The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. . . . Relativity actually says nothing about the existence or nonexistence of matter pervading the universe, only that any such matter must have relativistic symmetry. [..] It turns out that such matter exists. About the time relativity was becoming accepted, studies of radioactivity began showing that the empty vacuum of space had spectroscopic structure similar to that of ordinary quantum solids and fluids. Subsequent studies with large particle accelerators have now led us to understand that space is more like a piece of window glass than ideal Newtonian emptiness. It is filled with 'stuff' that is normally transparent but can be made visible by hitting it sufficiently hard to knock out a part. The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo.

Einstein wrote:We may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an Aether. According to the general theory of relativity space without Aether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this Aether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.

I believe there is more than enough proof that Space is not an Absolute Structureless Void. It is a Continuum, a real thing, and it has profound effects on Matter moving through it.

Is this where the confusion begins? That there doesn't seem to be a consensus on the validity of Space-Time being an Aether? This subject seems to divide Relativists into multiple camps. For too many reasons to list, I fully accept that Space-Time is an Aether (my Space-Wind from earlier). My primary objection to calling such a <Wind> is that it implies something that can blow past you while you are stationary. For the most part, it doesn't actually move, you are the one moving.

Personally, I like the Aether because it gives me something to sink my teeth into. Something that can explain how moving through it.. affects Matter and Energy and Clocks etc.

Vivian & Jocular:

Please ask questions. For every one of you that asks a question, there are many not brave enough to ask but still want simple answers. I can't think of any question you could ask.. that can't be answered in a simple fashion.

Best wishes all,
Dave :^)

### Re: Why is relativity so hard to learn?

Posted: April 29th, 2017, 1:15 am
Dave_Oblad » 29 Apr 2017, 02:04 wrote:As to the subject of my Space-Wind, we can call it Space-Time, Aether or even a Field.

Hi Dave, I'm more than a little concerned that what you are propagating is some distance away from what modern spacetime structure is. I'm all for having an explanation that everyone can 'sink their teeth into', but the one that you propose contains some serious flaws. It seems to be a combination of properties of the 'old aether' and the 'new ether', i.e. the structure of spacetime itself.

One example, your: Something that can explain how moving through it.. affects Matter and Energy and Clocks etc.

It obviously depends on how "moving through it" is defined, but as I gathered from all your writings so far, the elapsed times on clocks depend on how fast they are moving through your "Space-Time, Aether or even a Field". The modern relativistic view (for at least the last 50 years or so) is quite different. You have to know the paths that different clocks have taken through the spacetime structure, otherwise you cannot determine which one will record the least elapsed time.

You are running slightly ahead in this thread (which I don't mind), but the very next piece that I am preparing is about the structure of spacetime, as I have said at the end of the previous piece.[a] It will be about why there are differences in the structures of spacetime for different inertial observers and will (hopefully) lead to a more natural and trivial resolution of many of the 'paradoxical' explanations of relativity. I will attempt to show why your sort of description fails, why there is reciprocal time dilation observed by any pair of purely inertial observers and why the twins of the 'twin-paradox' really age differently.

-J

[a] I will go back and edit some titles by simply adding a numeric to the title of the start of a new 'piece', so that it is easier to refer to and follow my main ideas. If good ideas/criticisms come up in this community-effort, I will go back and issue updates, with credits. ;)

### Re: Under Arrest

Posted: April 29th, 2017, 3:20 am
Faradave » April 28th, 2017, 8:44 am wrote:Hi Dave,

As you describe it, the two ships on parallel paths are at rest with respect to each other. End of discussion!

You can say they're moving or not* wtr to some other reference frame but they each share the same one. They're like two opposite walls of Jorrie's mobile lab. I don't see the need for "space wind".

*because you're free to declare that "other frame" to be the one that's "moving".

Yes, aberration of light and "space wind" has nothing to do with that example.

Aberration of light would have no effect on the apparent position of the other craft because it is not moving in that reference frame. The whole analysis was caught up in thinking there is some kind of absolute motion.

Now here is what aberration of light will actually do...

1. If the other ship is moving faster (i.e with a positive relative velocity), then aberration of light will make it seem to be farther behind than it actually is.

2. If the other ship is moving slower (i.e. with a negative relative velocity), then aberration of light will make it seem to be farther ahead than it actually is. For the same reason, things towards which you are heading will appear farther away even though relativity tells us that they are actually closer because of Lorentz contraction. This gives the weird non-intuitive result that relativistic acceleration will actually look like you are going backwards (as long as you are looking forward).

When you look behind you, things look closer than they actually are. What you see behind you during acceleration is more complicated. I haven't done the calculation or programmed constant acceleration in my simulator but this is what I see when I hold down the engine button in the simulator moving away from earth: the earth seems to remain at a constant distance until time dilation causes it to move sidewise along its orbit around the sun. But that button isn't even a constant acceleration -- it is a proportional increase of velocity. So I would guess the aberration of light with a constant acceleration probably just causes the earth to appear to have a smaller acceleration away from you than it actually has.

### Re: Why is relativity so hard to learn?

Posted: April 29th, 2017, 4:13 am
jocular » April 28th, 2017, 11:09 pm wrote:
hyksos » April 27th, 2017, 3:51 pm wrote:

The early development of SR was actually extrapolating on electromagnetism as given by Maxwell's Equations. Maxwells equations are sine-qua-non for electromagnetism in physics. Well ... they are if all the magnets and wires involved are bolted to the laboratory desk. If you start moving around with magnets on moving platforms, and maybe even someone with a battery is moving along with said platform, Maxwell's equations break down.. and break down hard. This dirty secret is what Lorentz knew about, and where he enters stage left into this drama.

I have heard this but am finding it hard to find it discussed anywhere. You wouldn't have a link ,would you where this particular point is fleshed out?

Edit! On second thought. This video is, I believe the clearest elaboration of how Maxwell's equations break down hard under moving platforms.

Veritasium: "A magnetic field is really just an electric field viewed from a different frame-of-reference".

A more elaborate answer from Yale. Start at 41:40, where Dr. Shankar says,
Okay now you come to Maxwell's Equations for electromagnetic theory. Let me write down what we have. The first thing we have is F = q(E+... I'm sorry q times E plus V cross B is the force. And let me write down one other consequence.

Now comes the important question: This is the velocity of the particle according to whom?

If you like Shankar. Here is his whole lecture on relativity: https://www.youtube.com/watch?v=3enwR6e9V9A

### Re: Why is relativity so hard to learn?[1]

Posted: April 29th, 2017, 5:23 am
Thanks, I will give them a look.

### Re: Why is relativity so hard to learn?[1]

Posted: April 29th, 2017, 2:37 pm
Hi all,

This is starting to look like fun.

First, my personal view of Space-Time Aether is far from the one I'm presenting. And I won't present mine here.

One of my early mistakes (mentioned above) was the two ships running in parallel, separated by 1 light second of distance. I argued that the view from Ship(A) of the sister Ship(B) has a delay of 1 second for the light to bridge the gap, thus Ship(A) should be seeing where Ship(B) was.. and not where it is.

I got jumped on by a number of Members, all of whom said that Ship(B) would still LOOK like it is at a perfect right angle from the position of Ship(A).

Given:
Ship(A) & Ship(B) are at right angles with Zero Velocity. (Ref=CMB)
Ships are separated by 300,000 Km (one light second).
Ship(A) shoots Laser Beam at Right Angle Mirror.
Beam hits Mirror and bounces 90' to Ship(B) perfectly on Target.

Given:
Both ships then accelerate identically to 86% Light Speed simultaneously and go inertial.
Both ships are still at a perfect 90' angle from each other, coasting, on perfect parallel paths.

Graphic example of Ship Problem

No one argues it will take 1 second for a Beam to traverse the distance between them.
Both Ships can be said to Share the same Frame.

My argument was that Ship(A) should see Ship(B) further back, due to Light Transit Delay.

My argument was Ship(A) would have to lead (aim ahead of) Ship(B), to make up for the Light Transit Delay, to still hit the Target.

I am told I am wrong from at least 4 fellow Forum Members.
I am told both ships share the same Frame (despite the distance).

It was settled that Light Aberration was the reason Ship(B) still seemed to be at 90' from Ship(A).

It was settled that Light Aberration was why Ship(A) didn't need to aim (lead) ahead of Ship(B) to hit the Target on the side of Ship(B). That Ship(A) doesn't have to physically re-adjust the mirror angle on Ship(A).

mitchellmckain seems to debate the effect is <NOT> due to Light Aberration (which I had accepted).

So let's start the discussion on a SHARED FRAME with this simple example provided.

Question-1: Why does Ship(A) observe Ship(B) to still be located at a perfect right angle?

Question-2: Why does Ship(A) not need to lead the Target to make up for the Light Transit Delay?

It should not be debatable that Light Transit of the Laser Beam is instantaneous between Ships.

Please use simple English to explain the dynamics involved.

Will Jorrie and mitchellmckain agree?

Best Regards all,
Dave :^)

Note: I make no claim to be an Expert. I'm here to learn also. Much of my working Knowledge comes from fellow members on this Site (especially Jorrie).