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Showing content with the highest reputation on 12/26/19 in all areas

  1. 2 points
    As swansont has already stated, dark matter is matter that is hypothesized to exist due to the apparent gravitational effects we see, but which doesn't interact electromagnetically like the regular matter we are used to dealing with. This means it does not emit, reflect, or absorb light either, thus the description "dark". And as he said, we don't really know just what it is made up of yet. There are a couple of possibilities. Massive Compact Halo Objects (MACHOs) would be objects like neutron stars and black holes. These are object formed from "normal" matter (or at least a far as black holes go initially from it), but compact so much mass into a small area that they are just to small and dim to see individually. However, we need quite a bit of dark matter to explain observations, and there are reasons why we don't think the universe could have this much mass in the form of MACHOs, as it would have effected how the universe evolved, resulting in one that looks a bit different from what we see. Another possibility is Weakly Interacting Massive Particles (WIMPs) These are sub-atomic particles that have a rest mass, but just don't interact via the electromagnetic interaction. (And pretty much everything having to do with how we interact with regular matter, from touching it or seeing it, to chemical reactions involves electromagnetic interaction) These "ghost-like" particles would pass right through you like you weren't even there. While this this seems bizarre, we actually already know of a particle that behaves like this, the neutrino; Billions of them pass through you every day with your ever noticing it. Neutrinos ( or at least the type we know of) don't work for dark matter for various reasons, so the WIMPs of dark matter would be something like, but not identical to neutrinos. It is also possible that both of the above play a role in making up the total effect we see. swansont also mentioned attempts to explain things by a modified theory of gravity. The problem with this is that a number of observations are not compatible with such an explanation. An example would be galaxies that appear to be identical but exhibit different gravity profiles. Even if the rule of gravity were different than what we presently think they are, they would still need to be consistent from galaxy to galaxy. So while its perfectly possible for different galaxies to contain different amounts of dark matter and thus as a whole act differently in terms of gravity, it is hard to explain why the actual rules governing gravity would change between galaxies. Having said this, it is still possible for a modified gravity theory to play some role, if combined with dark matter. A new theory of gravity which also incorporates a mix of MACHOs and WIMPs could end up being the final answer. Right now we are at the stage of continuing to make observations in order to narrow the playing field. We have eliminated some possibilities, but there are more to explore.
  2. 2 points
    Recasting the theory of electromagnetism into a geometrical form is straightforward if you use the differential forms formalism. It then becomes simply \[dF=0\] \[d\star F=4\pi \star J\] This has already been known for a long time. For a (very) detailed discussion on the similarities and differences between electromagnetism and gravity when it comes to their respective formalisms, I refer you to Misner/Thorne/Wheeler, Gravitation, chapter 15, most especially box 15.1. All of this has already been recognised and worked out in detail. Essentially, the form of both models shares a common underlying principle, being the topological principle that “the boundary of a boundary is zero”; but because the basic objects involved are different ones, you end up with two models that also have a lot of differences. In spite of any similarities, electromagnetism does not work the same way as gravity does. I would really urge you to consult the above reference, since it seems to me that what you are trying to do is something that has already been done long ago.
  3. 2 points
    A clock near a black hole ticks at “1 second per second”, a ruler near a black hole is “one meter per meter” long. A clock on Earth ticks at “1 second per second”, a ruler near Earth is “one meter per meter” long. Locally in their own small enough neighbourhoods, neither observer determines anything special to be happing. As the name already implies, relativistic effects become apparent only when you compare clocks and rulers in different frames - they are relationships between frames, not things in and of themselves that somehow happen to clocks and rulers. No clock will ever tick at anything other than “1 second per second”, and no ruler will ever measure anything other than “1 meter per meter”, within their own local frames. Time does not “slow”, space is not “stretched”, they merely become local concepts. It is crucially important to understand this point. So, in order to determine the geometry of spacetime, you need to either compare clocks and rulers at different events, or (equivalently) observe what happens when they traverse extended regions of spacetime. What you find then is that different observers may disagree on specific measurements of space and time, but they will always agree on how those measurements are related to one another. In other words - all observers agree on the geometry of spacetime. Mathematically speaking, the object that quantifies relevant aspects of the geometry of spacetime (in GR that is the Einstein tensor) is something that all observers agree on, regardless of where and when they are, or how they measure and determine it. The components of the tensor vary as you go from one observer to another, but they vary in such a way that the overall tensor remains the same one - that is the meaning of “covariance”.
  4. 1 point
    Is this correct? mass = 37.2 g AICI3 (given) number of ions = AI3+ Ions (unknown) number of ions = CI- Ions (unknown) mass = g/formula unit AICI3 (unknown) The ratio of AI3+ Ions to CI- Ions is 1:3 Molar Mass AICI3 (1 x 26.98 g/mol AI) + (3 x 35.45 g/mol CI) = 133.33 g/mol AICI3 molar mass = 133.33 g/mol AICI3 Divide the given mass of aluminum chloride by its molar mass. 37.2 AICI3/133.33 mol = 0.279 mol AICI3
  5. 1 point
    scientist make a AI that can draw and paint... Well it looks like we have AI system that can draw and paint. https://www.christies.com/features/A-collaboration-between-two-artists-one-human-one-a-machine-9332-1.aspx Well it looks like AI that can draw and paint is coming out faster than we thought.
  6. 1 point
    ! Moderator Note Yeah, we keep banning you. The idea is supposed to be you don’t come back. You are not welcome at this site anymore
  7. 1 point
    ! Moderator Note We apologise for the oversight. But you must realise by now that sock puppetry is against the rules?
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