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    If someone figures out how to apply the principle of least action to spacetime itself, then perhaps that will be a new physics. The problem statement itself is not too mysterious so long as one can successfully formulate what action means in respect of spacetime itself. Certainly spacetime has a characteristic stiffness (which determines the speed of light), local curvature (which specifies the local gravity) and energy density (due to the quantum vacuum).

    I just found this. It is already on the radar, and is called the Einstein-Hilbert action for massless spacetime
    (5 mins in)
    When people want to explain spatial (or spacetime) curvature, in the manner of Gauss or Riemann, they usually draw a sphere to illustrate positive curvature, and a saddle to illustrate negative curvature. But why a saddle? Most of the directions you can take away from the saddle are of positive curvature!

    So I'd like to propose an alternative to this poxy saddle idea. Just take a sphere, and talk about moving around on the inside surface of it.

    Or, if the fact that it's a closed space bothers you, chop the sphere in half and talk about a bowl.
    • CommentTimeJan 10th 2016
    Doesn't work. Triangles on a positively curved surface have angles that sum to more than Pi. Triangles on a negatively curved surface have angles that sum to less than Pi. It doesn't matter whether you draw the triangles on the inside or outside of the sphere - angles still sum to more than Pi.
    Aha! You are right. I see this by imagining translating the outside triangle to the inside across the infinitessimal thickness of the sphere. It's the same triangle, of course.
    Piers depress me. You walk along them under the screeching gulls in the wind and then you get to the end. It goes nowhere. You are at the end of the pier. That's pretty much it for piers.
    • CommentTimeJan 17th 2016
    Not if you have a boat.
    And it's "infinitesimal".
    • CommentAuthorloreman
    • CommentTimeJan 17th 2016
    Piers are fingers pointing to the ocean and the sky
    • CommentTimeJan 17th 2016
    And the moletrap.
    • CommentAuthorloreman
    • CommentTimeJan 17th 2016
    Watching Heat (1995) and hearing rap. So it's over 20 years old.
    Dude, where have you been? More like 30 years.
    30 years of rap??? My god.
    Ever noticed that we know of no moons of moons? It's amusing to contemplate a semi-infinite amount of such regression. Stability? - you do the maths.
    Posted By: Andrew PalfreymanEver noticed that we know of no moons of moons?

    Au contraire

    • CommentAuthorLakes
    • CommentTimeFeb 11th 2016
    One of those moons needs eclipsing.
    • CommentTimeFeb 11th 2016
    Posted By: Andrew PalfreymanI think we are all fucked. Seriously - we're done with as a species.

    Did people think in a similar way after the invention of the atom bomb? Certainly, and world powers rushed to put safety measures into place. The thing about a nuclear bomb is that it's very hard to get the raw materials to make one, it's very hard to actually build a working one, and if you manage to deploy it, everyone will know you did it.

    Not so with the latest gene editing tools. The expertise required can be acquired by a high schooler in a few days. The raw materials are ubiquitous. And if you create something accidentally or deliberately that's bad, and release it into the wild, nobody can trace it back to you. And so there's no way to put safety measures in place.

    It only takes a single loonie with a single batch of - say - mosquitoes to change the mosquito genome forever, everywhere, using CRISPR plus gene drive. Once done, it's irrevocable.

    This is much worse than the nuclear bomb.

    I agree especially as I have been saying this for years, altered pathogens are at least two orders of magnitude worse than nuclear weapons.

    Self sufficient colonies in space and on planets and moons are essential for the human species survival.

    Underground and underwater bases might be helpful in the short term for various useful genomes.

    And all genome information should be kept top secret, even now it might be to late as nut job terrorists who genuinely believe they go to heaven if they die killing 'unbelievers' still have the smarts to make various deadly pathogens and insect vectors to spread them.

    They have the advantage as the are not worried about using prisoners as laboratory rats directly.

    What would you choose, point your bottom away from Mecca a few times a day or watch your friends and family die a horrible lingering death?
    I am not immune to Amygdalic Moments
    Even little Cuba provides free health care for all its people and it's of fairly high quality. The USA, richer than Cuba beyond measure, does not. Which country is truly more civilised?
    Posted By: Andrew PalfreymanEven little Cuba provides free health care for all its people and it's of fairly high quality. The USA, richer than Cuba beyond measure, does not. Which country is truly more civilised?
    How much golf do the Cuban doctors get to play?
    I rest my case