4 ms·
Doesn't need to be, but observations constrain extra spacial dimensions to be compact and under ~1mm in size.
by gobbo 11y ago
Doesn't need to be, but observations constrain extra spacial dimensions to be compact and under ~1mm in size.
- donutz 11y agoDoes anyone have a good way of explaining to a layman how a dimension can be small?
- sdenton4 11y agoImagine a cylinder. It has one flat direction, which goes on forever, and a curved direction which can have a very short circumference.
- aardvark179 11y agoConsider the outside of a straw. The surface is a curved two-dimensional space which is bounded in one direction only by the length of the straw, but is quite small in the other (the circumference of the straw). If the straw is very long and very thin then it may appear to be essentially 1-dimensional, but the surface is still two dimensional.
- DubiousPusher 11y agoNice example. Wouldn't there be easily measurable evidence of this? Imagine a flattened caterpillar like creature living on such a straw. Unwittingly, one day it might wrap itself round the straw many times. Looking back, seeing itself turned round the straw in this way, wouldn't it see slices of itself rather than a whole?
- evanpw 11y agoIn the caterpillar's universe, light rays wrap around the surface of the straw too, so they won't see anything "missing".
- DubiousPusher 11y agoAwww, of course.
- donum 11y agoFunnily enough, the same question is currently at the top of /r/AskScience: http://www.reddit.com/r/askscience/comments/42u57e/how_can_a_dimension_be_small/ http://www.reddit.com/r/askscience/comments/42u57e/how_can_a...
- xyzzy4 11y agoHow can a dimension be under a size? The four regular dimensions (3d and time) can go infinitely in any direction.
- fennecfoxen 11y agoWell, how can you go on forever without falling off the edge of the Earth? The surface of the Earth two-dimensional, and approximately flat... but there's small positive curvature, so you're continuously wrapping around to a different part of the space. The surface of the Earth can be meaningfully understood as a two-dimensional surface that possesses finite dimension. A three-dimensional space can be close to flat but have positive curvature as well (or negative curvature, for that matter). Some proposals give our universe positive curvature, rendering its space finite, though still stupidly-big. (I'm not aware of there being a final word on the subject, though). And if different dimensions can have different curvatures, some of them could be much smaller than others.
- gizmo686 11y agoMy understanding is that we have conducted experiments to measure the curvature of the universe, and come up with answers that are withing the experimental error of being flat. Without any theoretical reason why the universe should be flat, it is still possible that the universe is curved, but to slightly for us to detect, however, but the simplest interpretation is to say that the universe is flat. Of course, if we a assume a multiverse with universes having regularly distributed, positive curvatures, then, the size of the universe would grow asymptotically as the curvature approached flat, so, statistically, life is more more likely to arise on the flatter universes.
- vectorjohn 11y agoIs it possible, or in any way related, that a small but non-zero curvature could be responsible for the accelerated expansion of the universe? I don't know, it's hard to picture. But I'm thinking the idea that you can look at a sphere as a 2 dimensional space that curves and eventually wraps around such that things going opposite directions on its surface eventually can run into each other again. That would probably be more easily measured though. I don't know.