It’s Friday, and I’m sure you’re thinking about the weekend, so today will be just a review and some more details about the speed of light.
And speaking of light, today is the Vernal Equinox. For the next six months (for those of us in the northern hemisphere), our days will be longer than our nights. No doubt the combination of spring, the Equinox, and the weekend, have you wondering what you’re doing at your computer reading about Special Relativity.
I’ll try to be very brief…
Throwing like a girl!
I’ve introduced the idea of an inertial frame of reference. This is when we, and objects in our frame, are either standing still or moving with constant (straight-line) motion. In this situation, we can’t tell if we’re really moving or standing still relative to some other frame of reference. In fact, the question is meaningless.
I’ve also introduced the idea that objects moving within our frame — moving (or standing still) along with us, but also moving from our perspective — move differently from the perspective of other frames. Specifically, the speed appears different.
Now I’ll dig deeper into that and introduce a crucial exception.
In the last two posts I’ve explained how Special Relativity concerns relative motion between two frames of reference, and that the motion involved is constant, straight-line motion that allows us to view either frame as the “moving” one or the “standing still” one.
Today I’m going to dig a little bit deeper into the idea of relative motion and what that involves for actions within a constantly moving frame of reference versus what observers in a different frame perceive. In other words: trains, planes, and automobiles.
(Warning: this gets a little math-y, but you can ignore those bits.)
A fun way to feel acceleration!
Last time I introduced some of the foundation concepts required for our exploration of Special Relativity. In particular, that the word “special” in this case refers to a specific kind of motion: constant motion in a straight line.
Which may have caused some of you to wonder: Okay, what about motion that isn’t constant (and what’s that business about “in a straight line” — why keep mentioning that)? As it turns out, when motion involves speeding up, or slowing down, or going along a curve (or even just changing direction), that changes the situation in very significant ways!
That’s what I’m going to discuss today.
Okay, if you’ll all take your seats and quiet down, we can begin. I’ll keep this very short today because I know it’s Spring and many of you are eager to get out there and walk Frisbees and throw dogs… I mean — well you know what I mean.
The point is, that in keeping with spring, I’m aiming to keep these posts light and breezy. Unfortunately, I have terrible aim, so we’ll see how that goes. I never met a paragraph I couldn’t make longer!
Ready? Let’s go…
Terry Pratchett, 1948-2015, RIP
My mom died a year ago today. Yesterday I attended a memorial service for my best friend’s mom, who died this past February. Also in February, Leonard Nimoy took a final bow and exited stage left. Most recently — just last Thursday — another star went out, and it was one that shone brilliantly in the sky for so many of us.
Sir Terry Pratchett finally got to meet one of his key characters. I like to think that, for him, it might have been like meeting an old friend — and sadly, a visitor he’s been expecting for quite a while now. We fans know that Death personally attends the passing of wizards.
And Terry Pratchett was a wizard beyond compare.
Okay. I’ve been teasing doubly special Saturday and (especially this year) since last Monday (and planting hints along the way). If you haven’t figured it out by now, today is Albert Einstein’s birthday. It’s also pi day, and how cool is it that a guy like Al was born on pi day?
So: Happy Birthday Albert! The (especially this year) part is because it’s extra-special pi day (3/14/15) and because this year I’m finally going to do what I’ve been wanting to do here to commemorate Einstein’s birthday since I started this blog back in ought-eleven.
I’m going to write — at length — about Special Relativity!
It’s pi day! Be irrational!
Earlier this week I mentioned that “this coming Saturday is a doubly special date (especially this year).” One of the things that makes it special is that it is Pi Day — 3/14 (at least for those who put the month before the day). What makes it extra-special this year is that it’s 3/14/15— a pi day that comes around only once per century. (Super-duper extra-special pi day, which happens only once in a given calendar, happened way back on 3/14/1529.)
I’ve written before about the magical pi, and I’m not going to get into it, as such, today. I’m more of a tau-ist, anyway; pi is only half as interesting. (Unfortunately, extra-special Tau Day isn’t until 6/28/31, and the super-duper extra-special day isn’t until 6/28/3185!)
What I do want to talk about is a fascinating property of pi.
Computing…
I’ve written here before about chaos theory and how it prevents us from calculating certain physical models effectively. It’s not that these models don’t accurately reflect the physics involved; it’s that any attempt to use actual numbers introduces tiny errors into the process. These cause the result to drift more and more as the calculation extends into the future.
This is why tomorrow’s weather prediction is fairly accurate but a prediction for a year from now is entirely guesswork. (We could make a rough guess based on past seasons.) Yet the Earth itself is a computer — an analog computer — that tells us exactly what the weather is a year from now.
The thing is: it runs in real-time and takes a year to give us an answer!
I mentioned recently that I intended to write some “For The Record” (FTR) posts setting down — once and for all — my views on certain oft-debated topics. “Once and for all” is misleading, though. My opinions evolve over time, and no controversial topic is ever truly closed. “Here and for now” would be a better phrase.
This one will certainly draw a sand line where some will stand on my side and others — people I like and respect — will stand on the other. I’m not sure I believe there is a right answer here; it really depends on your worldview. If nothing else, this seeks to explain my rationale as well as my opinion.
So, for the record: here we go on guns!
Posts pertaining to programming!
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