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Posts posted by Endy0816

  1. 1 hour ago, random_soldier1337 said:


    Lol, I dunno. I just take people's word for these things. For all I know everything is an anime behind the scenes with cyborg ninjas and psychic super soldiers running around performing black ops, having death battles and philosophizing in the quiet moments, especially their death throes. Or maybe it's like a schoolyard with someone being nice and then someone being a jerk, "Hey you can't do that!" "Why not?" "Because you can't." "Sure I can." and that's all that happens.

    Anyway the project was supported by the IAEA.

    Yeah, might have been the IAEA. Considered a generally authorized destination for distributions(assuming I've parsed the legalese correctly).



  2. 2 hours ago, rjbeery said:

    GR's treatment of gravity already accounts for stellar motions and accretion discs without requiring event horizons. It's entirely possible that black holes exist, but then it's also possible that the center of galaxies are full of unicorns and lemon ice cream. If GR has "a number of failings with regard to BHs" then you have no model whatsoever to predict them.

    No. We know something has to occur due to the finite speed of light when density crosses the critical threshold.

    Other thing is nothing else can match a BH for compactness. Accretion disk of an equally massive star still can't orbit as closely.

    Whatever goes in is lost. Outside we never learn what has happened, if anything, past the Event horizon.

  3. 4 hours ago, rjbeery said:

    I have some problems/questions regarding the existence of black holes. First, here is the current state-of-affairs in the physics community AFAIK:

    1. Black holes "exist" in the sense that they are physical objects in the Universe
    2. Black holes contain an event horizon, located at the Schwarzschild radius, beyond which "nothing can escape"
    3. Black holes are likely located at the center of many galaxies, including our own; "micro black holes" are also likely formed and quickly evaporate in our atmosphere due to relativistic cosmic rays
    4. Quantum mechanics is anticipated to resolve any mathematical singularity issues at the center of black holes
    5. There are a variety of theories, most notably Hawking Radiation, that predict an "evaporation" of black holes over extraordinarily long periods of time

    Does anyone feel this any of these statements are inaccurate?

    The last is potentially inaccurate.

    Only fairly large ones take long periods of time.

  4. 1 hour ago, Airbrush said:

    "...temperature is the measurement of the average kinetic energy of the molecules and represents the motion of molecules."


    "...Based on observations of distant objects and measurements of the cosmic background radiation, scientists have deduced the temperature at the Planck time, which is 10 million trillion trillion trillionths of a second. At that instant, the temperature was 100 million trillion trillion kelvins (180 million trillion trillion degrees Fahrenheit). The universe underwent a period of accelerated expansion that ended well before a second had elapsed. By this time, it had cooled to a temperature of 100 billion kelvins (180 billion degrees Fahrenheit)."


    My question is how can the universe be so hot at the first Planck time  when the universe was so dense that the particles could not move? 

    BTW, at the center of a black hole are molecules in motion?  It seems to me that at near infinite density there is no space for motion.

    I think average KE would stay the same as they only have each other to run into.

    For the center of black holes the formulas fail to give meaningful values. Trying to find density, results in a division by zero situation, a mathematical singularity.


  5. 2 hours ago, swansont said:

    The problem I see is that Planck units are a unit system 


    “the system is internally coherent. For example, the gravitational attractive force of two bodies of 1 Planck mass each, set apart by 1 Planck length is 1 coherent Planck unit of force. Likewise, the distance traveled by light during 1 Planck time is 1 Planck length.” Notice how it’s not referencing any actual particles, or measured phenomena 

    I don’t understand why anyone is ascribing more significance. It doesn't seem to justified anywhere.

    You can do your exercise with other units. The SI energy density is 1 Joule/m^3.The cgs energy density is 1 erg/cm^3, which is not the same - the differ by a factor of 10. That’s OK, though, because there’s no physical significance here. 

    I have seen reference to the vacuum energy calculation from the Casimir effect, and from a particle in a box. Those have QM significance. 


    Yeah, often incorrectly thought of as the be all end all, when in some cases you can have even smaller measurements.

  6. 22 hours ago, swansont said:

    One thing that comes to mind is hostility toward the celebration of Columbus day.

    State adoption of MLK day was not unanimous, at the outset

    (edit to add: a push to remove Andrew Jackson from the $20 bill)






  7. 3 hours ago, Mordred said:

    That is a common error. We can predict far more than we can accomplish through technology.

     We know the limitations of space travel. We also know the consequences of near c velocities.

     The near c or greater than c velocities are incredibly problematic when you study the physics and time aspects. Even the Alcubierre drive has consequences such as gamma ray production. ( It could literally radiate your destination)


    Does the math say anything about causality issues if your travel was to somewhere in the Unobservable Universe?


  8. Buoyancy would be correct to use for both. Air and water are both formally considered fluids.

    Buoyancy is ultimately due to Earth's gravity pulling on whatever fluid you are displacing.

    Fluids: Archimedes' Principle | Paige's Physics Blog
    A simpler way to say it is:
    FB = mfl * g
    Buoyant Force = Weight of the displaced Fluid

    A wet-suit could help you to displace more fluid and increase your buoyancy that way.


    Net force would be the Buoyant force minus the object's own weight.


    Hopefully this helps, interesting question.



  9. On 5/6/2014 at 5:03 PM, MirceaKitsune said:

    This is one thing I was always curious about regarding the evolution of life and people. It's known that most things which define living beings descend from features that were essential for survival. We have limbs, eyes, ears, etc. because with them we could fight or escape predators (or be predators) and avoid dangerous environments. From a psychological point of view, we developed a language because it allowed us to work in teams and survive. Moving away from features essential to survival, people also developed activities / games / fun ways of passing the time, but which can also be explained as they satisfy certain features of the mind and body.


    For example, sport requires physical effort which in turn releases hormones related to positive feelings. Combining that with the joy of a victory, it makes sense from a biological perspective why sport existed since the earliest days of mankind. Or let's take art, which is a way for people to visualize scenarios which can't happen in their physical reality... a desire once again explainable by how the brain works. Yet there's one... which I can't understand how biology and the brain lead to, but which also doesn't feel like something learned; Music.


    It's an obvious fact... everyone likes music, and we couldn't imagine the world without it! Of different types and genres, by different artists, and for different messages it transmits. But unlike other things, it's hard to understand how this came to be. After all, music is just a precise arrangement of various overlapping sounds in a logical loop... with voice added on top in some cases. It also doesn't describe an actual place or object like drawn art, so it's not an efficient method of transmitting essential information. Somehow, the brain takes liking to translating those precise noise patterns, rather than finding it all a senseless sound.


    One could argue that our like for music might be taught. For example, the ancestors of humans would play the war drums to announce their people of an upcoming war. Not with the intent to compose music, but as a way of making noise to attract attention. From that, people could have later developed a liking for sorted beats. It sounds logical after all.


    But personally, I tend to disbelieve that. Primarily because no one is taught to like music. People like it simply because they like it... it's something which is part of them. Even if you take a man who lived isolated in a forest all his life and play him a nice song, he will enjoy it and not find it some gibberish noise. The official theory of evolution also ruled out the idea that learned experiences become part of the genetic code in offspring. Further more, it doesn't appear to be just a human thing either. I remember a cat expert confirming that symphonic music calms cats down and makes them feel happy. Yet to cats found in nature, nothing similar to symphonic music is ever heard, which could explain them associating the sound of a violin with a happy feeling... after all it's not that close to purring and meowing.


    So has anyone figured out how this works? What is it in our genes and the structure of the brain that makes us like music?


    One theory I've read is that it allows us to pick up on and mimic the various bird and animal calls. This would have given our ancestors a sizable advantage both in their own hunting and knowing when a predator was about.


  10. 3 hours ago, studiot said:

    Yes I agree, Turing took one of the many steps along the development of IT, he did not invent the Von Neuman architecture (I wonder who did that ?)
    Although originally a theoretical mathematician, Turing was also practical as evidenced by rewriting the intensively theoretical Godel theorems into a practical (if gedanken) setting).

    But modern IT is about more than just about one thing. It draws together many disparate aspects of technical knowhow.

    But it is difficult to list the many who contributed to the drawing together of the many different threads without missing someone out, or how far back to go in engineering history.
    For instance what would the internet be like without the modern display screen ?
    Should we include the development of these or printers or printing itelf? Fax machine were first invented in 1843.
    What about control programs? Turing is credited with the introduction of 'the algorithm'. But Hollerith invented the punch card in 1884.

    You need

    1. The laws of combination logic (Boole, De Morgan)
    2. The implementation of these in machines (Babbage, Hollerith, Felt)
    3. Methods of communication between machines (Bell , Bain, Hertz, Marconi)
    4. The formation of 'words' of data from individual combinations.
    5. Standardisation of these words  -  the language  (Bemer)
    6. Moving from mechanical to electromechanical to electronic implementations of data structures (Von Neuman)

    So here is my (draft) shortlist of the development, apologies for any omissions.

    Babbage  (1791 - 1871) the analytical engine
    De Morgan (1806 - 1871) De Morgan's theorem.
    Boole (1815 - 1871) Boolean algebra
    Bain (1810 - 1877) the Fax machine
    Bell (1847 - 1922) The telegraph telephone
    Hollerith (1860 - 1921) punch cards Braun
    Berliner (1851 - 1929) microphone (inter machine communications) - 1876
    Braun (1850 - 1918)  cathode ray tube (inter machine communications)  -  1897
    Felt (1862 - 1930) Comptometer 1887
    Von Neuman (1903 - 1957) Digital computer architecture.
    Bemer (1920 - 2004) Standardisation of digital words.  1961

    Interestingly names beginning with the letter B predominate, perhaps that was Turing's crime  -  to start his name with the wrong letter.

    Claude Shannon(1916-2001) Father of Information Theory, once teatime companion of Alan Turing :-)

  11. 18 minutes ago, studiot said:

    Building machines to decode enigma seems pretty practical to me?

    However I thank the OP for asking the original question since it resulted in my finding out something I did not know about Alan.
    His main purely theoretical work, an early prediction of chaotic behaviour, resulted in the discovery of B-Z reaction in chemistry.

    At one point he worked in/with Bell Labs even. I would still say that others were more instrumental in developing the internet itself.

  12. 40 minutes ago, Theredbarron said:

    holy crap!

    where is the end then? look I have always been the end but maybe where is the end of vacuum?

    where is the end if we cant get there?

    Pressure is force exerted over some area. Fewer or simply less energetic(lower temperature) atoms bouncing around and you get a lower pressure.

    Closer you get to zero and the more difficult achieving an accurate reading becomes. There's vacuum energy too ,which I think would prevent you from getting all the way to zero in any case.

    Can you upload a picture of the gage? You have probably drawn a decent enough vacuum for most things though never hurts to check.

  13. 21 minutes ago, DrP said:

    I read an article about those in a magazine a couple of years ago. Fascinating


    I'm mainly intrigued by their application to air purification in space. Huge game changer from needing to use amines, which both add complexity and leave the air smelling of ammonia.

  14. On 5/22/2020 at 4:17 PM, XVV said:

    What is the meaning behind multiplication in physics? Is multiplication in physics purely mathematical or there is a physical explanation to it? How do we explain the product for example, s=v.t? Is there any meaning behind this? For example, I can say that "Distance is defined as the product of velocity 'times' time"? But what does this even mean?

    You can express most things as an equivalent scenario, if that is what you are looking for.

    For S = V.t:

    If we measure Bill as traveling 50 meters every 10 seconds, how far would he go if he traveled for 60 seconds?

    Distance = (50 meters / 10 seconds) * 60 seconds

    I normally visualize the product as an intersection of two lines crossing. Something like the figure below.


    Line A might be our velocity and Line B might be the time for example. Where they cross is your product.

  15. 10 hours ago, Scienc said:

    Why does the equation τ = -n.R.T.ln⁡ (v_2 / v_1) only work for reversible processes? 

    Is that for isothermal expansion of an ideal gas?

    Some of the setup looks different, negative sign and use of tau symbol. Could of course simply be rearranged though.

  16. 48 minutes ago, MigL said:

    Tried cookies with grasshopper in them, once.
    Never again !

    I'm not against using them as a protein source for more 'traditional' livestock, like pigs, chickens, cows, etc.
    But feeding them to starving people, while we eat steak, seems kind of wrong.

    Considered a delicacy in some places, though food distribution could definitely be improved along with not causing the triggering droughts in the first place. Have read that chickens like them.

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