4 ms·
> Lots of nuclei have similar spin transitions, but only in thorium-229 is this cancellation so nearly perfect. > > “It’s accidental,” said Victor Flambaum(ope
by elihu 2y ago
> Lots of nuclei have similar spin transitions, but only in thorium-229 is this cancellation so nearly perfect.
>
> “It’s accidental,” said Victor Flambaum(opens a new tab), a theoretical physicist at the University of New South Wales in Sydney. “A priori, there is no special reason for thorium. It’s just experimental fact.” But this accident of forces and energy has big consequences.
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> Physicists have developed equations to characterize the forces that bind the universe, and these equations are fitted with some 26 numbers called fundamental constants. These numbers, such as the speed of light or the gravitational constant, define how everything works in our universe. But lots of physicists think the numbers might not actually be constant.
Putting these things together, if the physical constants do change over time, then perhaps there really isn't anything special about thorium-229, it's just that it's the one where the electrical repulsion and strong nuclear forces balance out right now. In a billion years maybe it would be some other element. Maybe we're just lucky to be alive at a time when one of the isotopes of an existing element just happens to line up like this.
Perhaps too there's an optimal alignment that will happen or has already happened when those forces exactly balance out, and maybe that would be an ideal time (or place, if these constants vary by location) to make precise measurements in the changes to these constants, much like a solar eclipse was an ideal opportunity for verifying that light is bent by gravity.
- vlovich123 2y agoYou’re assuming a monotonous linear change. It could be periodic or jumping between discontinuous values.
- benreesman 2y agoNot a physicist, just a passionate layperson. AFAIK real practitioners choose their units such that a lot of things are unity: speed of light is 1 (hence E = M), h-bar is 1, etc. There are some numbers like the “fine structure constant” (which I think is tantalizingly close to 1/137) that do seem difficult if not impossible to derive from others. The pop-science explanation for this that a layperson like myself would know about is the “anthropic” principal, they are such because only in such regimes would anyone ask the question. I don’t know what real scientists think about this.
- cryptonector 2y agoThe speed of light will always be seen to be the same no matter what, no matter where you are, no matter when you are. That's because we measure the speed of light with light, and we measure distances using light or light-by-proxy (because the electronic interactions that make normal forces what they are... electronic and subject to the speed of light, as is everything else). Other constants might change, but it would be very surprising if the speed of light (as observed locally) could possibly vary.
- mystified5016 2y agoSpeed of light can also be derived from the speed of a signal through a length of wire.
- jon_richards 2y agoI think the point is that if the speed of light changes, so does the length of the wire.
- cryptonector 2y agoBasically. I suppose that ε0 and μ0 could change in different ways such that c remains the same, or in different ways such that c does change but the change might be noticeable.
- oneshtein 2y agoWe can try to use gravitational waves (speed of gravitation propagation) to measure length.
- tsimionescu 2y agoGravitational waves travel at the speed of light as well. So if the speed of light changes, so would the speed of gravity waves, presumably - otherwise, they would probably not be equal today (though of course it could always be a coincidence).