Science Circa 2017

Discussion in 'Physics & Math' started by The God, Mar 16, 2017.

  1. The God Valued Senior Member

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    Let's keep medical science apart.

    Two points for discussions..

    1. Are we done with know all of science, is there any field where we know very little and much more work need to be done? Similarly what are the areas where we can safely say that we have mastered?

    2. Is there any need for alternative theory in any field of science. Any theory which requires overhauling but not happening due to various reasons?
     
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  3. origin Trump is the best argument against a democracy. Valued Senior Member

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    More can be learned in all fields of science.
     
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  5. Randwolf Ignorance killed the cat Valued Senior Member

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    No.
    Yes.
    None.
    Any theory that does not completely predict and describe all observations at all times under all conditions needs adjustment. Whether such adjustment constitutes an "overhaul" is a matter of perspective.
     
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  7. exchemist Valued Senior Member

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    As others have said, it is never "job done". This is because all theories in science are provisional and subject to review in light of new observations. As for theories needing overhaul, there are unresolved issues in all sciences, all the time. Theories are continually refined and tinkered with, every day.

    At the grand scale, there may be certain famous issues awaiting solutions .e.g quantum gravity, the mechanisms behind the origin of life and so forth. But there are thousands of smaller ones being addressed all the time.

    I think though that the notion of an "alternative theory" is a bit simplistic. There are lots of alternative theories already, in many branches of science, some of which, as I know from own discipline, happily co-exist and are drawn on depending on the task at hand.
     
  8. The God Valued Senior Member

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    Obvious answers will not develop into discussion. I will highlight the intent with medical science, which is a no go on this thread. The life expectancy has increased tremendously, thanks to substantial mastery over various diseases. But cancer is still a pain area, sudden cardiac arrest is also a sore point, HIV vaccination is a WIP..but on the other hand we have mastered the treatment of TB, Leprosy, Polio, Pneumonia etc which were major causes of death few decades ago.

    Let's extend this to physics, astronomy, chemistry, maths....at the theory level, not at the individual problems.
     
  9. Xelasnave.1947 Valued Senior Member

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    I would like a theory to replace inflation.

    I have raised this many times so this should not be a surprise.


    We dont know how big the Universe may be but just trying to imagine that the Observable Universe could have grown from something very small to at least a minimum size of approx 100 billion light years dia. seems beyond belief, to me.
    And it seems the Universe is much much larger than a dia of 100 billion light years possibly infinite.
    I cant see how one can double finite to become infinite so if infinite would that fact rule out inflation.

    Now obviously science does not need to change to suit me but I find it curious that no one in science has not offerred a more believable theory.

    It is my understanding that inflation fixed a major concern with BBT that threatened to see BBT fail.

    No doubt it was a relief to have someone save BBT via the creation of the theory of inflation and in my view folk have kicked back and not sort to come up with something more realistic.

    I dont think inflation has observational support and yet it survives.

    I know common sence plays no part but am I the only person who finds the concept that something can grow from the size of a mellon to near all that is there today in a split second impossible to accept.


    So if there was any area that needs work my personal view is the theory of inflation.
    To me leaving inflation as an acceptable solution to solve the problems raised for BBT is like fixing a patch to BBT and never returning to effect a proper repair.

    Alex
     
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  10. The God Valued Senior Member

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    Let's take electron around nucleus.

    Bohr Model talks of orbital motion for electron around nucleus but QM has a different take. If we follow QM, which is a betterment over Bohr's, then why there should be an upper limit in periodic table. Why 137 or some text say 173 is upper limit for elements? In case of orbital motion, we can understand that for 137 to happen the ground most electron will violate speed of light, so 137 and above is ruled out.
     
  11. exchemist Valued Senior Member

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    5,806
    I think there may be a misunderstanding here. Any upper limit on atomic number will be due to the stability of the nucleus, relative to the stability of products of fission. https://stab-iitb.org/newton-mirror/askasci/phy05/phy05124.htm

    It will not be to do with the behaviour of electrons in the atom.

    Mind you, what you say about relativistic motion of electrons in large atoms is quite interesting. That is responsible for the colour of some heavy metallic elements such as gold, for example: http://www.fourmilab.ch/documents/golden_glow/ (CAVEAT: This is a chemist's description, which will annoy the hell out of proper physicists, as it is implicitly written in terms of "relativistic mass" - the idea that mass increases at relativistic speeds, which is now considered an outdated and potentially misleading way of thinking about what is happening. There, that should be enough to keep rpenner off my back

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    )

    Also, it is not a correct understanding to say that anything in QM would ever require electrons to exceed c. All that happens, as electrons move faster in the s orbitals of the heavier elements, is that the kinetic energy of electrons ceases to be well-described by the simple 1/2. mv² law and the relativistic formula* has to be used instead. This enables them to acquire the necessary k.e. to stay in orbitals that entail spending some time close to a high charge nucleus, without breaching c. So this cannot be the source of any upper limit to atomic stability.

    * KE = mc²{ (1-v²/c²)⁻¹ - 1}, derivation here: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/releng.html
     
    Last edited: Mar 17, 2017
  12. The God Valued Senior Member

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    In QM electron position is all probabilistic, refer Schrödinger's wave function, there is as such no reference to orbital speed. So how do you fix 137, if we talk of nuclear stability, then I am sure the maths would be there which will confirm that the number of protons >137 and nuclear force is overcome by electrostatic repulsion...coincidentally (?) the classical explanation would say that required orbital speed of 1s electron exceeds c with 137 atomic number. One more thing, do we consider relativistic electron mass while calculating the same?
     
  13. exchemist Valued Senior Member

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    5,806
    Correct, there is no fixed orbital speed defined in QM, but there most certainly is a kinetic energy term in the Schroedinger equation. This sits alongside an electrostatic potential energy term and the energy of the electron is the sum of these two, the implication being that the electron moves on a path that can exchange energy between these two forms, rather as an object on an elliptical orbit does, though without the path being defined precisely. You may note it was relativistic kinetic energy rather than speed that I was referring to, previously.

    Regarding nuclear stability as a function of atomic number, you'll need to ask a physicist: as a chemist I understand a fair bit about the behaviour of electrons in atoms and molecules, since that is what determines chemical bonding and hence the whole of chemistry, but nuclear reactions are not something I have ever studied.

    As far as orbital speeds in a semiclassical Bohr atom, I have never even thought about it because nobody beyond school level uses the Bohr model, since it does not work, even classically: an orbiting electron would be an accelerating electric charge, which should by classical radiation theory radiate, lose energy and spiral into the nucleus. This problem was in fact one of the original spurs to the development of the quantum theory of the atom.

    But certainly, unless one was some sort of anti-relativity crank, one would need any Bohr model calculation that one did - for fun, presumably , as it would serve no other purpose - to use relativistic mechanics, once the predicted speeds became a significant fraction of c.
     
    Last edited: Mar 17, 2017
  14. The God Valued Senior Member

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    Common sense does play a part, it is not something which we can switch off from our system. It is just that some of the phenomena are not experienced in day to day life or cannot be extended based on day to day understanding and hence common sense may not be applicable there.

    Coming to inflation, its a fix for Big Bang Theory, you cannot deny this if you accept Big Bang. Denial of inflation means denial of Big Bang...so you have to start from scratch.

    So I will flag that in your opinion BB is not the done thing. Right?
     
  15. The God Valued Senior Member

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    Relativistic Mass

    Maths is fine.
    But can we associate some physical significance here? The rest mass as we know is frame invariant, and mass cannot increase without adding baryons and leptons or say even DM, so certainly this relativistic mass is no mass as such. Can I say things around relativistic mass, although century old, ate vague? Requires cleaning? Can I simply say that at relativistic speeds the media (the vacuum) provides the resistance which gives an apparent impression of increase in mass?
     
  16. The God Valued Senior Member

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    If there is KE, then there is motion and if there is motion which is non orbital...then dynamics become dicey. Isn't it? Like can we have stable atoms with electron motions but non orbital type?
     
  17. exchemist Valued Senior Member

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    Again, I am happy to converse about the behaviour of electrons in atoms and about atomic and molecular QM.

    But if you want to go off into interpretations of General Relativity, again I am going to refer you to proper physicists.
     
  18. exchemist Valued Senior Member

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    Yes indeed. In the QM model of electrons in atoms there is motion but the path of the electron is indeterminate. We resort to maps of electron probability density, indicating areas where the electron in a given orbital spends a significant part of its time.

    In fact, in s orbitals, there is zero orbital angular momentum (yikes!). Classically this would make the electron fall into the nucleus. In QM it may even do this, only to pop out the other side! It is the case that for s orbitals the electron density at the nucleus is not zero, whereas for those with orbital angular momentum there is a node (a point of zero electron density) at the nucleus. I think this is quite cool: QM is saying something not dissimilar to the classical mechanics result, but sort of fuzzy, due to the wavelike nature of the distribution. You can maybe even picture the path of an electron in an s orbital as being like simple harmonic motion, repeatedly falling through the nucleus, out the other side and back again.
     
  19. Xelasnave.1947 Valued Senior Member

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    I am no scientist as we know but wouldnt an older universe replace i flation for example or perhaps the problem inflation sort to sol e was not there.. Heck all I can do is wonder. It wouldnt be starting from scracth at the very least you would be working back from CMBR.
    Not so fast. My speculation does not mean I reject our model.
    I read someplace that one should be able to entertain all ideas and I take that to mean my own ideas as well.
    I can think of steady state I like it very much but well its no longer preferred.

    Oh to be able to stand back and see it like a movie to watch and understa d everything as you look.

    Alex
     
  20. The God Valued Senior Member

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    Physicist can jump in. Its chemistry also. I am well conversant with periodic table, electron configurations like all spdf stuff and sub orbitals. The original question is why periodic table is stuck at 137? What is the type of motion of electron if it is not around nucleus. Why we are satisfied that stable energy states do not radiate?
     
  21. exchemist Valued Senior Member

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    OK. The question about the Periodic Table is really one about max stable atomic number or atomic mass, which is, as I say, one of nuclear physics. The Periodic Table is not itself "stuck" on any maximum number in principle (one can write electronic shell structures without any limit), but I understand that in practice heavier nuclei start to be unstable compared to smaller ones, leading to spontaneous fission and shorter and shorter half-lives for the transuranic elements.

    Re electrons in atoms, nobody says the motion is not around the nucleus: it is. It is just that the path is indeterminate (this is the Uncertainty Principle again). And for s orbitals the average motion corresponds to no net orbital angular momentum.

    We are satisfied that stable energy states do not radiate because that is what we observe. So the problem needs to be put the other way round: to be satisfied, we need a model in which stable states do not radiate. And thanks to QM, we have that.

    Don't forget the object of science is to model reality as we perceive it to be through observation, not to make models that fit other models, or which make us feel comfortable.
     
  22. The God Valued Senior Member

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    Good.

    The last para is a nice way out.
     
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  23. exchemist Valued Senior Member

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    Haha, but it is a deeply serious point, not just a "way out".

    Here is Feynman on the subject:
     

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