Spoonfed Relativity
by Jonathan Doolin
General Relativity
by Bruce Linnell

Spoonfed Relativity: Special Relativity Tutorials

Special Relativity Tutorials

Hi! Welcome to the Spoonfed Relativity Website. This project was started around 1999, I put together several Interactive Flash demonstrations while I was learning Special Relativity (and Flash), and posting to alt.relativity on Usenet.

If you are looking for introductory material, these Flash Demonstrations are , in my not-so-humble opinion, STILL some of the best demonstrations of Special Relativity on the internet. Back in the day, when you searched Google for Special Relativity demonstrations, my flash demonstrations were on the first page of search results.

Sadly, I lost that website when I moved, as it came from my internet provider, rather than from a permanent hosting site. I've also lost a lot of the source-code from the original demonstrations, so I can't easily go in and fix simple things like broken links. So all the internal links from the flash demonstrations are broken.

Since that time, I got two Master's degrees; one in physics in 2004, and then one in math in 2008. Though I haven't had much time since then, I've made a few pages here and there; most of them come from 2010 and 2011. In these pages, you'll find many animations, made with Mathematica, but you'll find less interactivity, and more mathematics. So, you might not enjoy these pages as much unless you are a math/physics whiz. But I think you will still find the animations enlightening.

As of June/July 2014, I have the summer off, so I expect that there will be a considerable amount of editing over the next few weeks. You'll find that if you click on Essays/Articles, above, you will see a list of pages, with the most recently changed articles listed first. And below, you'll find the .swf "Shockwave Flash" files, which are interactive demos with levers and buttons and stuff.

Thanks for visiting!

~Jonathan Doolin - June 7, 2014

New Material
This introduces a subtle but profound philosophical question on the nature of the "observer-dependency" of reality. (and introduces matrix multiplication.)
These questions give an immediate sense of what Special Relativity is all about, and let you struggle more with the aforementioned fundamental philosophical question of observer-dependence.
This article deals with a frequent criticism of my website, which claims that Lorentz Contraction is invisible.
This article is meant to distinguish between observer-dependent transformations and description-dependent transformations. This is a major source of confusion in most texts on General Relativity.
Here are some helpful geometrical constructions needed to understand how the speed-of-light can be the same for all observers, even though those observers don't need to be moving the same speed.
A list of all the articles on the web-site.

Interactive Demonstrations (circa 2001)
This was one of the first Flash demos I created: When you throw a baseball, you add the velocity of the ball to the velocity of the thrower. What would it look like if photons traveled like baseballs? What would it look like if you COULD travel faster than the speed of light?
At the beginning, this is a fairly traditional thought experiment introducing time dilation , but be sure to proceed toward the end of the demonstration: What if, instead of having one photon bounce back and forth between two mirrors, we take a whole row of them? Then you will begin to see the desynchronization effect in action.
This is one of my favorite demonstrations because it really shows all three of the fundamentals of Special Relativity; length contraction, time-dilation, and desynchronization. This demonstration considers a pulse of light emanating from the center of a large mirror, and returning to the center. What would it look like from the viewpoint of someone passing by at near the speed of light?
Explore the three different ideas of observer dependent speed of light, source dependent speed of light, and ether dependent speed of light.
How could scientists measure the speed of light? One method uses spinning wheels with a slit, demonstrated here.
Angles are not preserved in relativity, if I throw a baseall off the side of a moving truck, I see it go straight forward. Other people will see it traveling angled toward the truck's direction of movement. lets you have a look at this idea, modeled for Special relativity. Or you can view desynch.swf to see the demonstration uncluttered by instructions.
This quiz does not keep score, but explains each answer whether you get it right or wrong.

Animated Space-Time Applet (circa 2008) .

LT.htm has a java applet program that lets you manipulate a two-dimensional space diagram. It showed me some things I didn't even know existed, like the Rindler Coordinate System naturally arises from setting a constant acceleration. Now, believe me when I tell you, when I wrote this program, Java couldn't do ANYTHING... It was totally sandboxed. I couldn't open files, close files, save files, or anything. Apparently, since that time, somebody un-sandboxed java, causing all kinds of trouble, so now, with any default configuration, you cannot run a java file without it being on HTTPS, and having secure sockets layer. That's with good reason. You don't want to go trusting an application, willy-nilly, that can read and write files all over your hard drive. Unfortunately, until I decide I've got enough money to pay the Secure-Sockets-Layer salesman to tell your web browser that my free demonstration is safe to use, you are in the uncomfortable position of having to put full faith and trust in both me and my web service provider, going into the Java configuration and adding spoonfedrelativity to your trusted sites. And frankly, even I don't have full faith and trust in my web-service provider! But then, I'm paranoid. Whether you decide to change your default Java Security Configuration, or not, you can still watch the video, showing what the applet does.

Noninteractive demos (circa 2001)
In one of my less interactive, but more fanciful demonstrations, you can see the basic idea of how length contraction and time dilation interact.
Here we see a space-ship accelerate, forward and backwards. Technical: The phenomenon shown in this demonstration is not mere acceleration, but actually a "jerk" i.e. a sudden change in acceleration. As it turns out, a space-ship undergoing constant acceleration would settle comfortably into an equilibrium state. The analysis of that equilibrium is called Rindler coordinates.
After you watch cartoon.swf you can see an analysis in twins.swf

Pirelli "Relativity Challenge" Submissions (circa 2005)

In 2005 an Italian tire manufacturing company hosted a "Relativity Challenge" where the winner of the best web-based explanation of the Special Theory of Relativity would win a 25 000 Euro prize! I spent a good amount of time trying to improve what I already had created, and adding to what I had learned previously.

As you will see, I was working on a shoe-string budget when I made this. The free software covers over half the picture with an ad. Much of the animation in this video comes from the other flash demonstrations. There are also a few elements that are unique to the video itself.
This tutorial is a bit twitchy. Hover the mouse over a button, and you'll get a question. Click the button, and you'll get an answer. If you are not overwhelmed by the complexity of the interface, you could learn as much as I did making it!

Age.swf (circa 2001)
Apparently, General Relativity Experts all agree that the Big Bang isn't really a Big Bang, but just an "expansion of space." i.e. the galaxies are not really "moving apart," but rather the space in between the galaxies is stretching. This is all nonsense brought about by the idea of "arbitrary coordinate systems" which means that if you define your variables in a particular way, and you define "distance" in a particular way, then you can manage to trick yourself into thinking that the galaxies are all standing still.
I should point out that virtually everything on this website is controversial. The arguments about Special and General Relativity are nearly as heated as arguments about religion. There are many who believe General Relativity is flawed, some who believe Special Relativity is flawed. For me, what started as a quest to explain relativity has become more of a quest to explore relativity. There are so many unanswered questions; ideas that only seem to make sense halfway. The answers that are out there only apply if you ask them in a certain particular way.

Confusing or Overcomplicated Demos (circa 2001)
(some of the "errors" I point out here, I don't really think are errors.)
. (The points are not clearly labeled so its hard to see what's going on.)

Spoonfed Relativity
by Jonathan Doolin
General Relativity
by Bruce Linnell

Thank you for reading. My goal here is to present the theories of relativity as clearly as possible. That's not always an easy thing to do.
If you have slogged through my writings and demonstrations, I know it's been a lot of work for you! Still, I hope I have saved you some time because of the weeks, months, and years I've spent on this.
I hope you've found this to be helpful in your own research of relativity.
Please consider donating. I'll figure out some way to keep working on this project, in my spare time, but with your donation, I would be able to devote more time and resources to this project, and be encouraged to know it is valuable to others.

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