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 Topic: Ask a Physicist!

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  • Ask a Physicist!
     Reply #90 - January 08, 2017, 12:01 AM
    Quote from: ZackRazi on January 07, 2017, 04:04 PM
    Good thought! It is feasible, but fundamentally, as dense as a black hole is, it'd have to convert to a form of energy that's almost untraceable but also sufficient to potentially drive the expansion of the universe. I believe the characteristics of dark matter are such that it is unlikely that this is the case. As far as current Physics is concerned, dark matter began to exist since the moment of the big bang and continues to be present to this very day.


    Well, couldn't the energy be Dark Energy? Seems like there's a lot of that, too...idk, it's not like I can do mathematical modeling or really understand the physics on an intuitive level, my brain just throws random ideas around in random directions and waits for two things to collide and then assigns significance to those collisions on a randomized scale, but sometimes I feel like the ideas genuinely could be on to something (but the vast majority of the time, they're just total bullshit).
    Yea, though I walk through the valley of the shadow of death, I will fear no evil, for I have a sonic screwdriver, a tricorder, and a Type 2 phaser.
  • Ask a Physicist!
     Reply #91 - January 24, 2017, 03:40 AM
    I like this thread, the answers have been very illuminating Smiley. 

    Sorry for picking this question, I just had a go because I don't think anyone addressed it. 

    Quote from: Quod Sum Eris on August 08, 2015, 12:30 AM
    Isn't it supposed to have a shape, or a curve or something?


    In general cosmology, there is something called a FRW-metric, which is essentially an equation that describes the structure of the universe. It comes from Einstien's theory of general relativity when applied to the universe. In the equation, there is curvature parameter called K and hence dictates the geometry of the universe.

    K can have one of three values, -1,0,1

    -If the values is zero, then it means there is no curvature and the universe has flat of Euclidian geometry. This kind of universe can expand forever and can hence have an infinite volume.

    - If K is 1, then that means there is positive curvature and hence universe has a spherical geometry. This kind of universe has a finite volume and would essentially collapse back on itself. 

    -The last one is K=-1, this means the universe has negative or imaginary curvature and hence has a hyperbolic geometry. This kind of universe is thought to expand forever and has infinite volume as well (since its expanding).

     Current evidence suggests that the universe is likely to be flat i.e k=0 (this is worked out by finding the critical density of the universe). However this just universe on the local scale not essentially the global (the bigger part) as well.

    Hope that helps  Smiley.



    Lost somewhere between immensity and eternity is our tiny planetary home. [carl sagan]
  • Ask a Physicist!
     Reply #92 - January 24, 2017, 03:17 PM
    Quote from: Skeptic on January 24, 2017, 03:40 AM
    I like this thread, the answers have been very illuminating Smiley. 

    Sorry for picking this question, I just had a go because I don't think anyone addressed it. 

    In general cosmology, there is something called a FRW-metric, which is essentially an equation that describes the structure of the universe. It comes from Einstien's theory of general relativity when applied to the universe. In the equation, there is curvature parameter called K and hence dictates the geometry of the universe.

    K can have one of three values, -1,0,1

    -If the values is zero, then it means there is no curvature and the universe has flat of Euclidian geometry. This kind of universe can expand forever and can hence have an infinite volume.

    - If K is 1, then that means there is positive curvature and hence universe has a spherical geometry. This kind of universe has a finite volume and would essentially collapse back on itself. 

    -The last one is K=-1, this means the universe has negative or imaginary curvature and hence has a hyperbolic geometry. This kind of universe is thought to expand forever and has infinite volume as well (since its expanding).

     Current evidence suggests that the universe is likely to be flat i.e k=0 (this is worked out by finding the critical density of the universe). However this just universe on the local scale not essentially the global (the bigger part) as well.

    Hope that helps  Smiley.


    Thank you, superb answer! Friedmann, Robertson and Walker would be proud Smiley Sorry I might have missed this out (I am PhysMath, by the way).
  • Ask a Physicist!
     Reply #93 - January 24, 2017, 03:23 PM
    Quote from: gal_from_usa on January 08, 2017, 12:01 AM
    Well, couldn't the energy be Dark Energy? Seems like there's a lot of that, too...idk, it's not like I can do mathematical modeling or really understand the physics on an intuitive level, my brain just throws random ideas around in random directions and waits for two things to collide and then assigns significance to those collisions on a randomized scale, but sometimes I feel like the ideas genuinely could be on to something (but the vast majority of the time, they're just total bullshit).


    Haha that's actually how scientists often think. Throw ideas around, and wait for a collision...Though sometimes results are totally counterintuitive. Anyway that aside, back to your question. My point earlier was that it's unlikely that a black hole gave birth to it, but it isn't without reason. We think of black holes as the most massive units across the universe. We go by what we see and that's a limitation as much as a tool. There may be some other source other than what we perceive, and so once again I can only label it as viable rather than a solution. There is a way to mathematically calculate the energetics but the problem is, that will show *how much* of the quantity exists before the universe existed and thus how much energy was required to produce the source of the big bang. But not *where* that energy itself came from. There is just not enough information. I imagine the only way to do it is to try to see if there is some sort of energy signature (like Cosmic Microwave Background Radiation) to show what happened. I highly doubt we are any closer to finding the "right answer".
  • Ask a Physicist!
     Reply #94 - January 24, 2017, 05:29 PM
    is the world a hologram?
  • Ask a Physicist!
     Reply #95 - January 24, 2017, 05:30 PM
    are friends electric?
  • Ask a Physicist!
     Reply #96 - January 25, 2017, 02:40 AM
    Quote from: ZackRazi on January 24, 2017, 03:17 PM
    Thank you, superb answer! Friedmann, Robertson and Walker would be proud Smiley Sorry I might have missed this out (I am PhysMath, by the way).


    Hi Zack, glad you liked it  thnkyu

    And ha that will be like a dream come true  grin12

    And yea I figured it out when I was going through the thread Tongue.



    Lost somewhere between immensity and eternity is our tiny planetary home. [carl sagan]
  • Ask a Physicist!
     Reply #97 - January 25, 2017, 03:08 AM
    Quote from: Quod Sum Eris on January 01, 2017, 01:12 PM
    Do you think it'll ever be possible to warp space to the point we could, say, crunch up 20 light years of distance to X and reach that distance in X space of time rather than however long 20 light years would take to cross?


    I am going to add a bit to this question along with Zack's answer.

    What you are saying is allowed by Einstien's theory of General relativity.

    Relativity gives rise to a structure of causality. There are somethings called light cones and particles or say a ship has to travel through it to keep causality intact. The track that the particles travels is called its worldline. Look at the picture below for an illustration.



    If you look at the plane, that is the present moment in time, the cone beneath it is the past and the one above it is the future. A particle that has mass has to have a worldline(travel) inside this cone.

    Now light to has a worldline, and its the straight 2 straight lines that make up the light cone. I hope you have followed me so far, because if you understand this, the rest is easy.

    Now anything that is traveling at the speed of light, will be traveling on that straight line, Einstien tells us that nothing can travel outside of the light cone. Which is commonly stated as nothing can travel faster than the speed of light.

     Now the last part is not strictly true. Because what you can do is tilt the the light cone so that it makes a 45 degrees angle (just an example) with the plane. An illustration is below.



    So you can see how the light cone above the surface (future light cone) is tilted. Now compare the worldline of light in the previous light cone to this one. If you travel through the tilted light cone, your worldline will be outside of the light cone in the first image but inside the 2nd one. This means that you are traveling faster than the speed of light but in inside the light cone.

    Now imagine a space-ship surrounded by a bubble. This bubble is wrapping spacetime in such a manner that the lightcone inside the bubble is tilted, but the lightcone outside of the bubble is not affected. So because of wrapping of space-time, you can travel faster than the speed of light.

    This is allowed by General relativity and such geometry of space-time is described by something called the Alcubierre metric (looking it up if you want to go in more depth). Now the problem is, is it physically possible?

    The answer is, as far as we know, sadly it isn't. The reason for this is, to have such a geometry, you need to have negative energy-matter for which there is no empirical evidence so far.


    Hope this helps and I didn't up confusing you more Smiley.      

      



    Lost somewhere between immensity and eternity is our tiny planetary home. [carl sagan]
  • Ask a Physicist!
     Reply #98 - January 31, 2017, 05:00 AM
    Quote from: ZackRazi on January 01, 2017, 01:39 PM
    Haha, you're not far off. There are solar winds, so I'd bet there are cosmic events that cause "winds" in space-time. I'm also betting on there being cosmological events that cause ripples in space-time that would be useful for propulsion, a bit like waves on the sea. As long as the tide moves in the same direction. There is energy everywhere, basically, but containing it or structuring something useful out of it would be a tall order. Sorry to not be able to give exact answers, but that's because currently there are none.


    Anyone else picturing space pirates? dance

    When people talk about the shape of the universe, the curve and whatnot, is this an actual thing, or a concept created to understand, ala tree of life? Not literal. I don't understand how we can measure something possibly infinite or how something infinite can expand or have a shape. Or is this one of those times scientists are using words differently than how we normally think of them, i.e. as with the comments on nothing a couple of pages back.
    `But I don't want to go among mad people,' Alice remarked.
     `Oh, you can't help that,' said the Cat: `we're all mad here. I'm mad.  You're mad.'
     `How do you know I'm mad?' said Alice.
     `You must be,' said the Cat, `or you wouldn't have come here.'
  • Ask a Physicist!
     Reply #99 - February 25, 2017, 02:01 AM
    Quote from: Quod Sum Eris on January 31, 2017, 05:00 AM
    Anyone else picturing space pirates? dance

    When people talk about the shape of the universe, the curve and whatnot, is this an actual thing, or a concept created to understand, ala tree of life? Not literal. I don't understand how we can measure something possibly infinite or how something infinite can expand or have a shape. Or is this one of those times scientists are using words differently than how we normally think of them, i.e. as with the comments on nothing a couple of pages back.


    The idea of curvature is related to the "local geometry". So for example, in a point in space-time, do we have a "flat universe", meaning the angles of a triangle add up to 180°. Or does it have "negative curvature", meaning the angles add up to less than 180° in a triangle? Or "positive curvature" meaning angles add up to greater than 180°. I just use the triangle for illustration's sake. The general idea is the "shape" affects the mathematical tools that people use to measure things. It's no good to use the geometry rules of a flat universe in a curved one, or vice versa. It's purely for accuracy of measurements and calculations.
  • Ask a Physicist!
     Reply #100 - February 28, 2017, 12:28 AM
    Quote from: Quod Sum Eris on January 31, 2017, 05:00 AM
    Anyone else picturing space pirates? dance

    When people talk about the shape of the universe, the curve and whatnot, is this an actual thing, or a concept created to understand, ala tree of life? Not literal. I don't understand how we can measure something possibly infinite or how something infinite can expand or have a shape. Or is this one of those times scientists are using words differently than how we normally think of them, i.e. as with the comments on nothing a couple of pages back.


    STOP ASKING COMPLICATED QUESTIONS  Cry



    Lost somewhere between immensity and eternity is our tiny planetary home. [carl sagan]
  • Ask a Physicist!
     Reply #101 - March 26, 2017, 07:45 AM
    Wait, doesn't that mean that you have to have something else to measure it by? The only way to really measure infinity, I would imagine, is another infinity. Which would mean you have different types and and sizes of infinity. Which I suppose would only be possible with a specific understanding of what infinity is.

    So I would suppose you're meaning infinity in the sense of a racetrack, where you can drive a car (or motorbike if I have my say) with an unlimited power source around and around without end, without ever running out of track, rather than a straight road going a singular direction without end?

    Or have I misunderstood?

    Quote from: Skeptic on February 28, 2017, 12:28 AM
    STOP ASKING COMPLICATED QUESTIONS  Cry


    No. Tongue
    `But I don't want to go among mad people,' Alice remarked.
     `Oh, you can't help that,' said the Cat: `we're all mad here. I'm mad.  You're mad.'
     `How do you know I'm mad?' said Alice.
     `You must be,' said the Cat, `or you wouldn't have come here.'
  • Ask a Physicist!
     Reply #102 - May 04, 2017, 06:26 AM
    Could we 3D print gasoline?
    Yea, though I walk through the valley of the shadow of death, I will fear no evil, for I have a sonic screwdriver, a tricorder, and a Type 2 phaser.
  • Ask a Physicist!
     Reply #103 - May 13, 2017, 10:21 AM
    Quote from: Quod Sum Eris on March 26, 2017, 07:45 AM
    Wait, doesn't that mean that you have to have something else to measure it by? The only way to really measure infinity, I would imagine, is another infinity. Which would mean you have different types and and sizes of infinity. Which I suppose would only be possible with a specific understanding of what infinity is.

    So I would suppose you're meaning infinity in the sense of a racetrack, where you can drive a car (or motorbike if I have my say) with an unlimited power source around and around without end, without ever running out of track, rather than a straight road going a singular direction without end?

    Or have I misunderstood?


    You have only misunderstood on the aspect that you think when people say the universe is flat, they mean the *whole thing* (like a table) is flat. What they mean is we have tried applying the flat geometry mathematics to different places in the universe locally and it appears flat. The expansion of space makes it seem flat. So we'll say the universe is flat. And seeing it is flat at many places (ie that mathematics works) is the reason they use terminology like "it is flat", so it is more inductive than deductive. Much of science works inductively. We might find that the entire universe is a lot like a table, then, where there's roughness at smaller and smaller scales! And thus isn't "flat" overall, just seems it on the scales we are looking at.
  • Ask a Physicist!
     Reply #104 - May 13, 2017, 10:22 AM
    Quote from: gal_from_usa on May 04, 2017, 06:26 AM
    Could we 3D print gasoline?


    It would be possible in theory to 3D print anything. It would just be highly impractical. It would take more energy to 3D print it than to just extract it, I would reckon.
  • Ask a Physicist!
     Reply #105 - May 14, 2017, 02:44 AM
    Yay, you're back! dance
    `But I don't want to go among mad people,' Alice remarked.
     `Oh, you can't help that,' said the Cat: `we're all mad here. I'm mad.  You're mad.'
     `How do you know I'm mad?' said Alice.
     `You must be,' said the Cat, `or you wouldn't have come here.'
  • Ask a Physicist!
     Reply #106 - May 14, 2017, 02:49 AM
    Quote from: ZackRazi on May 13, 2017, 10:22 AM
    It would be possible in theory to 3D print anything. It would just be highly impractical. It would take more energy to 3D print it than to just extract it, I would reckon.


    I'd just watched two programs on the impending oil crisis and the possibility of 3D printing various molecules, and I was kind of thinking about what the production rate would have to drop to to make 3D printing gasoline a viable solution to the oil crisis and whether or not we could capture and recycle atmospheric CO2 to do that, killing two birds with one stone. But that's just my bipolar-induced overly lateral thinking and doesn't take into account the cost of doing an of that.
    Yea, though I walk through the valley of the shadow of death, I will fear no evil, for I have a sonic screwdriver, a tricorder, and a Type 2 phaser.
  • Ask a Physicist!
     Reply #107 - May 14, 2017, 03:32 AM
    Quote from: gal_from_usa on May 14, 2017, 02:49 AM
    I was kind of thinking about what the production rate would have to drop to to make 3D printing gasoline a viable solution to the oil crisis and whether or not we could capture and recycle atmospheric CO2 to do that, killing two birds with one stone.

       First of all gasoline is not something comprising of a single kind of molecule like water. It’s mostly a mixture of low-boiling-point alkanes that contains 5~11 carbon atoms in their molecular structures. So it’s not practical to 3D print it.
       Anyway it’s not worth it. We are not using gasoline as major fuel because it’s the best, but because it’s most easily accessible. Alcohol for example is a better choice if the time come that we had the leisure of 3D printing our fuels.

      A for capturing CO2 to make fuel, I believe there are many microbiologists and chemists working on it. I think we will see progress on that first in chemistry. I would have to make some research to see how far along it’s going, but there is already success in using CO2 to make plastics (the plastics industry is a big petroleum consumer so it helps to save petroleum); there is a brand called converge® that was launched in 2014 by Novomer and was acquired by Saudi Aramco.
  • Ask a Physicist!
     Reply #108 - June 07, 2017, 06:56 PM
    Here's another one of my insanely weird questions...assuming the many worlds interpretation and that our entire cluster began at the big bang, would the number of universes in our cluster actually be infinite? I would think that it's uncountable, sure, but not infinite, because fundamentally it can be calculated if we could just fill in the relatively simple multiplication problem: units of planck time since the big bang x quantity of quantum particles x possible positions of quantum particles. As far as I know, those are the factors determining the number of universes in the many worlds hypothesis and none of them is infinite, even if they're all too large to count.
    Yea, though I walk through the valley of the shadow of death, I will fear no evil, for I have a sonic screwdriver, a tricorder, and a Type 2 phaser.
  • Ask a Physicist!
     Reply #109 - July 01, 2017, 09:11 PM
    Another many worlds question! Assuming the many worlds interpretation of quantum mechanics, how often would I need to survive to become immortal? Lemme demonstrate that....when I'm suicidal I like to think about all the worlds in which I'm already dead (I find it comforting and it makes me less suicidal, it's not very intuitive). And recently I've been thinking about a universe where I die once per split. So it's a simple shrodinger's cat scenario, you open the box and there's one dead me and one live me. Assuming we stop experimenting on the corpse (because there are no more tests in which it is alive), after doing the experiment 15 times, there are now 14 dead mes and only one live me.

    Breakdown:
    Experiment 1 -- 1 dead 1 alive
    Reset the experiment using only 1 alive me, leaving 1 corpse
    Experiment 2 -- 1 dead 1 alive
    Reset the experiment using only 1 alive me, leaving 2 corpses (one from the previous experiment, one from this experiment)
    Experiment 3 -- 1 dead 1 alive
    Reset the experiment using only 1 alive me, leaving 3 corpses
    etc.

    Assuming the chances are 2/3 that I survive instead of 1/2, after fifteen experiments experiments there are 3 live me and  14 dead me.

    Breakdown:
    Experiment 1 -- 2 alive
    Reset the experiment (doesn't matter if you start with 1 alive, 1 dead or 2 alive because you'll end up with 3 alive, experiment # -2 dead after no more than 3 tests)
    Experiment 2 -- 1 alive, 1 dead | 1 alive, 1 alive
    Reset the experiment using 3 live subjects
    Experiment 3: 1 alive, 1 dead | 1 still dead | 1 alive, 1 alive
    Reset the experiment using 3 live subjects
    Experiment 4: 1 alive, 1 dead | 2 still dead | 1 alive, 1 alive
    Reset the experiment using 3 live subjects
    Experiment 5: 1 alive, 1 dead | 3 still dead | 1 alive, 1 alive

    So how often would I need to survive to be alive exactly as often as I'm dead? What percent of the time do I need to survive to make an equal pile of live me(s) and dead me(s)? I'm sure there's a simple equation but I haven't figured it out yet.
    Yea, though I walk through the valley of the shadow of death, I will fear no evil, for I have a sonic screwdriver, a tricorder, and a Type 2 phaser.
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