How do we know that the fundamental constants were the same during the early phases of the universe? Like the gravitational constant and the plank’s constant
In other words are the fundamental constants not a function of space time ? How do we know so?
Changing unit-full constants is not physically meaningful, since choice of units is arbitrary. But physicists do put limits on the rate of change of unitless constants, like the fine structure constant, or gravitational coupling constant. There are many ways of doing this, and I’m not an expert on cosmological studies, but you can, for example, look out at distant stars (which are in our past), look at their spectral lines, and put some pretty stringent limits on how quickly the fine structure constant can be changing with time. Similarly for the gravitational coupling constant, you can, for example, look at carbon-dated rocks (billions of years old) and show that they couldn’t have formed the way they did if the gravitational coupling had changed more than so and so.
To give a concrete example: Dirac at one point posited that the strength of gravity relative to the other forces was changing over time, in a particular way. But if you do the calculations, you find that if gravity were changing in that way, then a billion years or so ago, the Sun would have been significantly hotter, and the Earth’s orbit would have been significantly closer to the Sun, with combined effect that all the seas would have boiled off. But we find fossils of sea life that are that old and more, and so we know that gravity hasn’t been changing in the way that Dirac thought.
Now, is it possible that it didn’t change the way Dirac thought it would, but that it did change just a little tiny bit? Absolutely. There’s nothing in science that you can prove is exactly zero; the best you can prove is that something (in this case the rate of change of fundamental constants) is very close to zero, smaller than some limit that’s imposed by experiments. As experiments get better, that limit will get tighter, but it’ll never reach zero.
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You cannot carbon date rocks - Carbon dating is used to date material that exchanges carbon with the atmosphere when alive, and stops when it dies. In general, this means land-based plant matter or the remains of animals that live on such plant matter. The maximum age for carbon dating is ~60000 years. Radiometric dating (Potassium-Argon, Uranium-Lead, Uranium-Thorium) is used to date rocks, and can be used to date rocks billions of years old.
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Si
Or of course, just maybe, the limit could get tighter around a non-zero value. That would be not exactly expected, but very very interesting. But whatever value things tighten around, that value is already constrained by existing experiment to be very very small.
Yeah, I tend to use “carbon-dating” colloquially as a catch-all for all types of “Radiometric dating” (of which carbon is an example), since that’s the one most people are familiar with. But yeah, I should probably I have been more specific…
Although, some rocks are of biological origin, and in such you could still date when the organisms involved died (which may or may not have been close to the time when the rock formed).
Natural nuclear reactors have been used to check if the fine structure constant was different.
Thank you for the great replies. It seems though that the verification is limited to the age of the earth - which is great but still relatively does not cover the age of the universe.
An earlier thread of mine
http://boards.straightdope.com/sdmb/showthread.php?t=439007&highlight=hubble+photographic
This is still restricted to dating material less then ~60000 years old. At that point, C[sup]14[/sup] in the sample is at background. Also, some processes can increase C[sup]14[/sup] - Carbon dating of diamond and coal (very old carbon) can give C-dating ages of less than 60000 years. The obvious explanation is that subterranean radioactive exposure has increased C[sup]14[/sup] content above surface background - simple isotope analysis of other elements in the sample can confirm the isotopic shifts.
Studies to verify the constant value of the Fine-Structure Constant include astronomical observations as well as the aforementioned natural reactor studies. The results are still unclear - there may have been a change in the Fine Structure Constant, but if there was, it was very small (5 parts in a million). Research is ongoing.
Si