When Einstein Was Bohemian(blogs.scientificamerican.com)
blogs.scientificamerican.com
When Einstein Was Bohemian
https://blogs.scientificamerican.com/observations/when-einstein-was-bohemian/
17 comments
This was great. Something that bugs me about relativity is, how is speed measured relatively? I can imagine how it looks if both objects are on a straight line, one moving away from the other. What about objects in a plane, where one moves but never intersects the other?
Sorry if this question sounds nonsensical. I'm having trouble explaining a very graphical question.
Sorry if this question sounds nonsensical. I'm having trouble explaining a very graphical question.
It's not nonsense, but remember that speed is absolute so we just find the change in distance between A and B for a very small amount of time.
If you want a test without an abstract definition of length, then the Doppler effect is a way.
If you want a test without an abstract definition of length, then the Doppler effect is a way.
Just to be clear, the issue with relativity you're having is not particularly related to Special or General relativity - but classic relativity.
> What about objects in a plane, where one moves but never intersects the other
Just imagine standing next to the highway - the cars are not driving directly at you - but you can still tell they're going fast. You know where they are relative to you, and how that value changes over time, which gives you velocity. If I sprint next to the cars, they increase or decrease in speed relative to me of course. They don't change speed relative to Earth, which makes it easier to be a little objective about their speeds.
Think of it this way. In the black void of space. No stars, no nothing. There's me and you. We're 20 feet apart, but getting closer together at a constant rate. From my perspective, you're getting closer to me. From your perspective, I'm getting closer to you. Both of us can effectively measure each others speeds. Even if we're not parallel - if we're perpendicular, it'll still be similar.
What may be tripping you up is rotation. If I spin in circles, is that the same as everything else spinning in circles around me? If I were to go to a parking lot and spin around quickly, like a ballerina - what's happening to the cars? Well, one second, there's a car 50 feet behind me, the next second, it's 50 feet in front of me! You might think it just traveled 100ft per second relative to me! But this isn't the case. We can determine who is rotating and who is not, even in our black void. Rotation is not relative, it is absolute.
Take our black void example again. Except this time, we're both still, but you're spinning. From your perspective you see me floating 10 feet away from you, quickly orbiting you. You might think this is a relative situation - are you spinning, or am I rapidly orbiting you? But it is in fact, objectively true that one of us is spinning and the other isn't. How can you tell? Well, a number of ways.
For starters, it doesn't make sense for me to be orbiting you. There's no gravity at play, we could measure and feel that if it were the case. So if this illusion is to work, I must be zipping around you on my own accord, using my own energy somehow - like a little jetpack. But even still! Even with that ambiguity, you could tell you were rotating.
You can feel it in your arms, for one! Centripetal force will cause your arms to fly out, the faster you spin. Contrast this with floating in a straight line in our void. You could be flying by at 1000m/s or crawling at .1m/s and not know the difference without a reference point. Rotation, you can always figure out without a reference point. Rotation is absolute.
> What about objects in a plane, where one moves but never intersects the other
Just imagine standing next to the highway - the cars are not driving directly at you - but you can still tell they're going fast. You know where they are relative to you, and how that value changes over time, which gives you velocity. If I sprint next to the cars, they increase or decrease in speed relative to me of course. They don't change speed relative to Earth, which makes it easier to be a little objective about their speeds.
Think of it this way. In the black void of space. No stars, no nothing. There's me and you. We're 20 feet apart, but getting closer together at a constant rate. From my perspective, you're getting closer to me. From your perspective, I'm getting closer to you. Both of us can effectively measure each others speeds. Even if we're not parallel - if we're perpendicular, it'll still be similar.
What may be tripping you up is rotation. If I spin in circles, is that the same as everything else spinning in circles around me? If I were to go to a parking lot and spin around quickly, like a ballerina - what's happening to the cars? Well, one second, there's a car 50 feet behind me, the next second, it's 50 feet in front of me! You might think it just traveled 100ft per second relative to me! But this isn't the case. We can determine who is rotating and who is not, even in our black void. Rotation is not relative, it is absolute.
Take our black void example again. Except this time, we're both still, but you're spinning. From your perspective you see me floating 10 feet away from you, quickly orbiting you. You might think this is a relative situation - are you spinning, or am I rapidly orbiting you? But it is in fact, objectively true that one of us is spinning and the other isn't. How can you tell? Well, a number of ways.
For starters, it doesn't make sense for me to be orbiting you. There's no gravity at play, we could measure and feel that if it were the case. So if this illusion is to work, I must be zipping around you on my own accord, using my own energy somehow - like a little jetpack. But even still! Even with that ambiguity, you could tell you were rotating.
You can feel it in your arms, for one! Centripetal force will cause your arms to fly out, the faster you spin. Contrast this with floating in a straight line in our void. You could be flying by at 1000m/s or crawling at .1m/s and not know the difference without a reference point. Rotation, you can always figure out without a reference point. Rotation is absolute.
Thank you, this is really interesting. Never considered the absoluteness of rotation before.
But any two points are on a straight line, and with a suitable choice of the coordinate system there remains no "plane" to speak of.
I don't know if this is what you're asking, but X,Y find change of distance between these two points per unit of time?
Also check out this essay Einstein wrote in May of 1949,
https://monthlyreview.org/2009/05/01/why-socialism/
https://monthlyreview.org/2009/05/01/why-socialism/
'bohemian'[1] and 'Bohemian' are two very different cultures.
[1]: https://en.m.wikipedia.org/wiki/Romani_people#Exonyms
[1]: https://en.m.wikipedia.org/wiki/Romani_people#Exonyms
From the article:
> I do not mean the disheveled unconventionality often ascribed to him—I mean “Bohemian” with a capital B.
> I do not mean the disheveled unconventionality often ascribed to him—I mean “Bohemian” with a capital B.
The article doesn't really explain the difference merely saying Bohemia is a historical kingdom.
i read this title as Bohmian!! (as in David Bohm)
If you're looking for a book, I can recommend this one.
Bonus: Read "The making of an atomic bomb" by Richard Rhodes [1] before reading the Einstien biography. This book sets up the context and several key characters really well (and Einstien lurks in the background).
Also - Randall Munroe's explanation for the general theory of relativity[2] is a must read.
[0] https://www.amazon.com/Einstein-Life-Universe-Walter-Isaacso...
[1] https://www.amazon.com/Making-Atomic-Bomb-Richard-Rhodes-ebo...
[2] https://www.newyorker.com/tech/annals-of-technology/the-spac...