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 Topic: Ask a Physicist!

 (Read 5857 times)
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  • Ask a Physicist!
     Reply #90 - January 08, 2017, 12:01 AM

    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. 

    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

    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

    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

    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

    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

    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

    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

    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]
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