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imatfaal

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Posts posted by imatfaal

  1. Reminds of the thing a few years back; a ball with another ball inside. It could count how often the inner ball went around, and I had friends who spent ages and ages getting very excited by how high they could get that count.

     

    I just couldn't see the point. There was an exercise component, but not much.

     

    I would quibble on the lack of exercise component. Once you learned the technique to get the ball moving quickly you could generate enough angular momentum in the weighted inner ball that a fair amount of torque was required to hold and twist the ball in any other direction than around axis. I knew several sportsmen and women who used them to improve grip - and to provide exercise as part of rehab from injury.

     

    It was a hell of a lot less passive than the fidget spinners


     

    That's presuming we are talking about the same sort of things; I was referring to a Powerball (and no - I wouldn't have known the name without looking either) like this

     

    powerball-blue-lightning-the-original-0-

     

    I dug mine out of the cupboard of junk - a minute or so later I think my forearm would testify that the exercise component was not null

     

    post-32514-0-17751000-1495972613_thumb.jpg

     

     

  2. You appear to conflate "religion" with "belief in Gods" which has not been historically true. There have been, and are today, religions which focus on how people should treat each other irrespective of whether on believes in the existence of one or more Gods. I think "How people should treat one another" will alway be a concern as long as there are people.

     

    Which one? I don't wish to "true Scotsman" the argument, but if there is no supernatural element to a regimen of behaviour it is an ethical system - not a religion.

     

    There are the Quakers and the Universal Unitarians - who both have sizeable proportions of their congregations who are atheists - but as an organisation they "welcome" and "find space" for secularism; thus showing the existence of a (perhaps unimportant) demarcation between those members who are secular and those who are not, and that the organisation as a whole is non-secular.

  3. Not to be picky, Strange, but...

     

    The Schwartzschild radius ( or size of the EH ) clearly has a 1/c^2 dependence.

    ( although you could argue that is an inverse, square relation and not a direct relation )

     

    I was gonna post that too but decided that it was not quite right. Dependency is a term (normally) reserved for the relationship between a variable and another (set of) variables - but c is not a variable. I wuld say that that G/c^2 is the constant of proportionality of the relationship between r_S and M; I would not say that r_S depends on c in a mathematical sense - only in a plain language usage of the word.

  4. I saw a discussion of black holes of different sizes having differing gravity forces at the event horizons, but if the horizon is established by C, and C is constant, shouldn't the gravity at the surfaces be equal?

     

    Good question.

     

    By the way - a word to the wise; most people will realise you mean the speed of light when you write C (upper case), especially in this context - but the speed of light should be designated by c (lower case). It seems pernickity to mention it - but misuse of terms, units, and symbols can snowball into a real misunderstanding very quickly (even at the highest levels); it is best to practice precision as much and, as soon as possible.

  5. Actually not. It is a very clever analogy ... :)

     

    Indeed - on an amazing resource/website*. I have used that page to help explain before as well; for some reason, the analogy works even though it is not really any simpler than the real world scenario it is mirroring.

     

    * Will we lose this sort of thing under the present/proposed cutbacks - it can't be expensive to run but also it will not be costless. Sorry very [ot]

  6. !

    Moderator Note

    The side-chat, casual insults, and logical fallacies in this thread - from all viewpoints - was fairly disappointing. Thread Locked - we should be able to have a discussion on religion without resorting to such teenage antics. Please try to keep the signal to noise ratio a little higher in future.

     

    !

    Moderator Note

     

    Calling out the troll

     

    From my understanding, if you label someone as a troll you are claiming they are arguing merely to annoy and frustrate the other members of the board; the internet maxim is Don't Feed the Trolls - you highlight the problem and then withdraw. A report using the handy system provided will often sort this problem out. If, however, you label your counterpart in a discussion a Troll and then continue to argue with this member then this is an argumentum ad hominem; you are attempting to diminish the argument of the other member by attacking her or his character and motivation.

     

    There is no place in Scienceforums.net for any form of logical fallacy especially not one which relies on adversely characterising or stereotyping another member. Please bear this in mind whenever the temptation is to start name-calling of any sort. Thanks.

     

  7. What David proposed in post #2 is not "Sieve of Eratosthenes".

     

    Sieve of Eratosthenes pseudocode is

    https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes

     Input: an integer n > 1.
     
     Let A be an array of Boolean values, indexed by integers 2 to n,
     initially all set to true.
     
     for i = 2, 3, 4, ..., not exceeding √n:
       if A[i] is true:
         for j = i2, i2+i, i2+2i, i2+3i, ..., not exceeding n:
           A[j] := false.
     
     Output: all i such that A[i] is true.
    
    (it's begging for using bitwise logic operations and 8 times decrease memory needed for array)

     

     

    What he proposed in post #2 was something like:

    list.append( 2 );
    for( int i = 3; i < n; i++ )
    {
      bool found = false;
      for( int j = 0; j < list.count; j++ )
      {
        if( ( i % list[ j ] ) == 0 ) // modulo
        {
         found = true; // divisible by some prime
         break;
        }
      }
      if( found == false ) list.append( i ); // append yet another prime to array..
    }
    
    Output array contains nothing but primes.

     

    But better would be to skip the all even numbers, since the beginning:

     

    list.append( 2 );
    for( int i = 3; i < n; i += 2 )
    {
      bool found = false;
      for( int j = 1; j < list.count; j++ )
      {
        if( ( i % list[ j ] ) == 0 ) // modulo
        {
         found = true; // divisible by some prime
         break;
        }
      }
      if( found == false ) list.append( i ); // append yet another prime to array..
    }
    

     

    OK they both make sense to me - thanks, and well spotted; I must admit I was so annoyed at the fallacies I just skipped the description of the algorithm.

  8. I think of the CMB as just the background echo from the expansion "inflation" of the Big Bang. That's why I don't see it as having a source or distance away from us, it's just everywhere and has varying "degrees" of energy. And what does that energy tell us about the distribution of energy and matter at the beginning of measurement? That things were unevenly distributed. So, if the current theories are accepted, that there may be black holes aat the root of of quasars... so an unevenly distributed Universe with packets of gravity stronger than the inflation, couldn't preserve portions of the Big Bang in little pockets that might look something like quasars?

     

    The inflationary epoch was around 10^-36 of a second to 10^-34 of a second after the big bang - ie a frightening short period in the very very first instances after the big bang. The CMB was formed 380,000 years after the big bang in the era of recombination / the surface of last scattering (I just love those two oh-so poetic names).

     

    The variations in the CMB are tiny by the way - one part in about ten thousand would cover all variation; that is pretty homogeneous.

     

    Any black holes formed way way after the era of recombination ( the universe was almost homogeneous then - see above on CMB which is a reflection of the universe at that point.) Until an enormous time had passed we didn't even have hadrons - they only formed at the earliest estimation around a millionth of second after the big bang - the universe didn't see stars until 150 million years or so after the big bang. The earliest black holes were just so long after inflation that we cannot envisage them in the same context

  9. It was deleted as spam - the text was copied from wikipedia and the link was very very dodgy


    This was the text

    Gold(III) chloride, traditionally called auric chloride, is a chemical compound of gold and chlorine. With the molecular formula Au2Cl6, the name gold trichloride is a simplification, referring to the empirical formula, AuCl3. The Roman numerals in the name indicate that the gold has an oxidation state of +3, which is common for gold compounds. There is also another related chloride of gold, gold(I) chloride (AuCl). Chloroauric acid, HAuCl4, the product formed when gold dissolves in aqua regia, is sometimes referred to as "gold chloride" or "acid gold trichloride". Gold(III) chloride is very hygroscopic and highly soluble in water as well as ethanol. It decomposes above 160 °C or in light.

     

    At first glance it seems to have been lifted wholesale

    https://en.wikipedia.org/wiki/Gold(III)_chloride

  10.  

    Yes... so how does electron degenerate matter fuse? I always hate it when I order white wine and they bring red.

     

     

    The matter in a white dwarf which is under the chandrasekar limit (1.39 Solar Masses) is held apart by the electron degeneracy pressure - if it were actively fusing it would be held apart by the thermal pressure involved with such a high temperature; you reach this situation when there is not much left to fuse together (the sun has run out of fuel) AND there is not enough inward gravitational pressure to continue fusion.

     

    Matter in a white dwarf star which is above the chandrasekar limit and is running out of fuel will also get to the point where the only thing against the gravitational pressure inwards is the electron degeneracy pressure outwards - but for these heavier stars the gravity "wins" and electron degeneracy pressure is overcome and other things can happen depending on its make up and any companion; most spectacularly Super Nova

  11. The sieve of Eratosthenes has nothing to do with factorisation.

     

    I think the answer to the question is that the time for each division operation is not the problem; it is the number of operations required.

     

    Agree completely - I have looked at the Number Field Sieve algorithms and I just cannot work out what is really going on; most of this form of algorithm seem to have a choke point regarding the number of operations required rather than the difficulty of the operations involved.

     

    Further to the OP - the really place of study should be Shor's Algorithm; real world quantum computing has arrived. Whilst it is at a pre-difference engine level of development at present it will become viable. Shor's algorithm is proven to work in polynomial time - whereas the General number sieve works in sub-exponential time

  12.  

    None the fastest way is called the Sieve of Eratosthenes it involves using an array. It still involves trial division but less off it. First you add two to an array. Then you work through your array testing divisibility. If you get to the end of your array then the number is prime and is pushed to the end of the array. This is a parralelisable operation for instance you can test for the divisibility of all numbers in an array up to the computer resources you have available and then the runtime becomes a polynomial multiple of the resources you have. There is the problem that after a certain point the primes take too much hard drive space so the Sieve of Eratosthenes won't work anymore and you are back to using trial division. The Sieve of Eratosthenes can be used to show that Primes are in P on a turing machine (theoretical computer with infinite resources) P=NP but most computers don't have infinite resources. If you just use multiplication the range of numbers you can possibly calculate on a normal computer decreases by a lot because you are even more limited by hard drive space. There is also a limit on using trial division which is basically if something takes longer than 20 years to calculate your computer will break. There is also the idea that today's limitations may not be limitations in the future new methods of data storage could become available which make just using the sieve the more viable option.

     

    the Sieve of Eratosthenes is a prime number finder (ie it finds all the primes within a certain range) - not a method of factorization. The Sieve of Eratosthenes is not even the fastest at doing this once the size of the range / largest number of the range get large ~10^14

     

    The fastest way to factor difficult products (those of two primes of a similar size) is the General Number Field Sieve or the Special Number Field Sieve (if your number fits its parameters).

     

    Please do not write guesses like P=NP in the main fora - it is irresponsible and misleading.

     

    None of your post deals with computational complexity properly

     

    https://en.wikipedia.org/wiki/General_number_field_sieve

  13. You need to read up on "Frame Dragging".

     

    The Kerr Metric (this is a vacuum solution to the Einstein Field Equations - ie General Relativity) described spacetime around a black hole with angular momentum - ie a spinning black hole. So yes a spinning black hole does "drag spacetime around"

     

    It does not need to be spinning at the speed of light - in fact it cannot be as nothing which has mass moves through space at the speed of light - it just needs to be massive and be spinning. A central spinning mass will entrain the inertial frame such that it is affected by the central masses rotation; it is a gravitational effect - but that must also be seen as an acceleration effect of an inertial frame.

     

    Here is Clifford Will's write up of the experimental proof of frame dragging - Gravity Probe B

     

    https://physics.aps.org/articles/v4/43

  14. I heard about this but am not familiar with the details. Is it possible at all to explain to a layman how these paradoxes were inferred from relativity? I assume the mathematics of it cannot be put into simple form since they must be complicated, judging by the fact it took so many years to figure it out.

    That mathematical singularities ("divide by zero error" ) existed was known very soon - use of Schwarzchild Coordinates at the Event Horizon to give stopped time is a common example. But these involved calculational procedures that might be wrong. It was also known that certain unphysical scenarios would lead to physical singularities - but doubted whether any of these would actually manifest. Hawking showed they happned in actuality

    This is not a good page - but I am struggling to find one. https://en.wikipedia.org/wiki/Penrose%E2%80%93Hawking_singularity_theorems

  15. The structure of neutron stars is complex and fascinating. I seem to remember lots of pasta analogies (spaghetti, lasagna etc)

     

    - The pasta thing made me remember a good page for Neutron Stars

     

    Anyway, imagine starting at the surface of a neutron star and burrowing your way down. The surface gravity is about 10^11 times Earth's, and the magnetic field is about 10^12 Gauss, which is enough to completely mess up atomic structure: for example, the ground state binding energy of hydrogen rises to 160 eV in a 10^12 Gauss field, versus 13.6 eV in no field. In the atmosphere and upper crust, you have lots of nuclei, so it isn't primarily neutrons yet. At the top of the crust, the nuclei are mostly iron 56 and lighter elements, but deeper down the pressure is high enough that the equilibrium atomic weights rise, so you might find Z=40, A=120 elements eventually. At densities of 10^6 g/cm^3 the electrons become degenerate, meaning that electrical and thermal conductivities are huge because the electrons can travel great distances before interacting.

     

    Deeper yet, at a density around 4x10^11 g/cm^3, you reach the "neutron drip" layer. At this layer, it becomes energetically favorable for neutrons to float out of the nuclei and move freely around, so the neutrons "drip" out. Even further down, you mainly have free neutrons, with a 5%-10% sprinkling of protons and electrons. As the density increases, you find what has been dubbed the "pasta-antipasta" sequence. At relatively low (about 10^12 g/cm^3) densities, the nucleons are spread out like meatballs that are relatively far from each other. At higher densities, the nucleons merge to form spaghetti-like strands, and at even higher densities the nucleons look like sheets (such as lasagna). Increasing the density further brings a reversal of the above sequence, where you mainly have nucleons but the holes form (in order of increasing density) anti-lasagna, anti-spaghetti, and anti-meatballs (also called Swiss cheese).

     

    Taken from here M Coleman Miller's Introduction to Neutron Stars

  16. If you make an arragement of atoms in the tightest way possible, due to their shape (even though that term is very loose), there will be some gaps in matter, or ''micro-vacuums''. Therefore, there must be such a thing as the highest possible number of atoms that can be fit inside a space of certain dimensions before the nuclear force is broken down.

    But the nuclear force can be broken down, something that happens when a black hole is forming.

     

    Even in a neutron star there are no atoms (or precious few) - the gravitational pressure is such that protons and electrons fuse via electron capture create neutrons. The whole star is neutrons held apart by neutron degeneracy pressure which is basically the outcome of the pauli exclusion principle

    ...

    To my understanding, the singularity of a black hole (if there is such a thing) is thought to be comprised of just matter with no gaps in structure. This would mean that the space it occupies is occupied in whole, without the possibility of it getting denser. If any more matter is added to it, its volume will grow but not its density. My question is, why is then ''maximum density'' not something that exists in physics? The singularity IS thought to have infinite density, but this is a result of the equation p = m/v where v = 0, hence p = infinite, and not what I am talking about.

     

    the Singularity is something which is predicted in General Relativity (Hawking and Penrose) - but the existence of the singularity is normally taken as a sign that beyond event horizon is out of scope for GR; ie you need a new theory to properly deal with this.

    ...

    Furthermore, if all singularities are the same size, how can some have more distant event horizons than others? You could say that some have more mass, but how could they have more mass if their size is zero and density infinite?

     

    What piece of information am I missing? Thanks in advance for any helpful replies.

     

    "What piece of information am I missing?" That we know next to nothing about what happens behind the event horizon and definitely not what is going on at the singularity - or possibly more accurately, and definitely not what is actually there instead of a physical singularity

  17. I don't see how it is 'fringe science' as you put it.... it is a real and measured effect (from what I read briefly - I could be wrong). The explanation for the effect may be clearly wrong and provably so - but that doesn't mean the effect doesn't happen. There is probably some perfectly reasonable explanation for it - like most things.

     

    But the "science" is not the effect - it is the explanation of the effect; it is the model which allows you to understand the effect in terms of simpler well-known causes.

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