Oh, that's not what I meant. I meant use the reference frame from when you first woke up. But I'll make a more detailed scenario:

* Wake up in the void. Label your current reference frame R0.

* Notice that there is no real way to label 'speed' vs. void.

* We can however measure angular speed via tension on body parts, it seems to be 0.

* Accelerate somehow

* * for some magical reason it's forbidden to have more than one object, so I thought up a couple minimally-magic ways to do it that I am pretty sure don't cause physics problems by themselves.

* * * You could throw something then immediately pretend the thing you threw doesn't exist, forbidding it as a reference frame.

* * * You could make a punching motion and use magic to cause your arm to disappear.

* * * You could swing all your limbs away from your body and use magic to reverse the direction of one of them.

* Now you are in reference frame R1 because you accelerated.

* Hooray you accelerated without any other objects to compare to. If you insist on comparing to a reference frame, use R0.

>* * * You could swing all your limbs away from your body and use magic to reverse the direction of one of them.

No you can't, this leads to the twin paradox. Assume you could use magic to simply reverse the direction of an object. Take two clocks, and have one travel away from you at relativistic speeds, then turn around and come back. Because of time dilation, when the clock returns, it will have observed less time pass then you, because it was moving at relativistic speeds. However, from the clocks perspective, you were moving at relativistic speeds, so you will have observed less time pass. The resolution to this paradox involves the fact that the clock was accelerated in order to turn around.

An interesting side point is that in the hypothetical void, you actually have no way of knowing weather or not you are accelerating. For example, the space station is currently in free fall towards the earth, but from within the station you cannot detect this fact. Similarly, if you are in a plane that is descending at the rate of gravity, you will appear to be in zero-g. The mathematics behinds this is considerably more difficult than special relativity.

You're talking about accelerating. The original passage was just talking about simple constant motion. The point being that you can't distinguish constant motion from remaining perfectly still without something else to measure against. That's really all I was trying to say. Obviously I failed!

For what it's worth I think you did a good job overall, but flaws are pretty much inevitable when your word choice is so restricted.

The point the original author is implicitly trying to make is that you can't compare to your original frame, where you went to sleep.

This is the part I'm objecting to:

To move, you have to move to or away from ... well, from what? You'd have to say that you don't even get to use a word like "move" when you are the only body in that void.

You can move. You can have a delta v. You don't have an absolute position or velocity, but you don't need those to move.

I don't see any comparison to the pre-sleep state, this is a statement about the void, and it overreaches.

This is a metaphor breakdown because you pushed it too hard, rather than a real problem with the idea. In the ideal case you are a floating point, and you haven't got discrete parts of yourself to fling away, but of course that's an abstract step too far away for the target audience of this piece.

Reflections on Relativity [1] in fact does build up to a generalize concept of relativity (not just Einsteinian relativity) starting with points in an unknown space (building up to a concept of distance, rather than assuming such a thing), but it's a mathematical treatment of the problem rather than an intuitive one. And certainly not in words of one syllable.

[1]: http://mathpages.com/rr/rrtoc.htm , the part I'm referencing starts right off at 1.1.

I think I haven't made it clear enough what my objection is. In my opinion it is the article that pushed the analogy too far. It works great to show that you can't tell what is moving. But when the analogy tries to claim that you can't move, well, it's pretty much begging the question. Of course a floating point can't move, and it says nothing about physics. That's why I assumed some mechanism for trying to cause motion: you can't see if you failed if you didn't try.

I guess I wasn't clear (no sarcasm). My point is based on the idea objecting that an analogy doesn't stand up to being pushed "too far" isn't a useful one; analogies always break down when pushed too far. If they didn't, they wouldn't be analogies, they'd be explanations. Analogies are dangerous ways of thinking, but again, this is generally targeted at people for who that is all they have available.

The analogy is useful, I agree there. The problem is that the article first uses the analogy for something it fits, then uses the analogy again for something it doesn't fit. The conclusions drawn from the second use are invalid. I don't object to the analogy, I object to that second use.

I had the same objection as the op actually - if you wake up at "rest" with just yourself and a bed, and accelerated away from the bed, you can in fact know whether "you are moving" or "the bed is moving". It is because one of the two have only been in 1 reference frame, while the other has been in 2.

Basically the same issue as the twin "paradox". I can appreciate the assumption of a constant velocity on wake though, as a way to simplify the story.

I don't think you can accelerate in an empty universe - no speed, no speed difference.