Please turn on javascript in your browser to play chess.
Science Forum

Science Forum

  1. Standard member sonhouse
    Fast and Curious
    18 Feb '16 15:59
    http://phys.org/news/2016-02-gravitational-glimpse-ripples-big.html

    I got to thinking. If there is a huge amount of energy expended to make these gravity waves the size of the universe, could that alone explain the expansion noted from about 5 billion years ago?
  2. Standard member DeepThought
    Losing the Thread
    19 Feb '16 09:54 / 2 edits
    Originally posted by sonhouse
    http://phys.org/news/2016-02-gravitational-glimpse-ripples-big.html

    I got to thinking. If there is a huge amount of energy expended to make these gravity waves the size of the universe, could that alone explain the expansion noted from about 5 billion years ago?
    The waves they are talking about come from the end of the inflationary era. At that time the radius of the universe was of the order of 1 metre. They would be powered by the inflaton field going into its ground state. The subsequent expansion is just coasting and since the gravitational waves have a wavelength of the order of the size of the early universe they are stretched out with it. If you are suggesting that the observed acceleration of the expansion of the universe is actually due to a gravitational wave with a period of the order of the life time of the universe then it's an intriguing possibility. I don't see why not, but the initial amplitude would have to be huge. Then again inflation generates almost all the energy in the universe so I don't see why not.

    Edit: Actually I do see why not, it wouldn't be isotropic. So I've changed my mind - I don't think that there's a simple connection between these early waves and the observed acceleration of the expansion of the universe.

    Edit 2: Also gravity waves are waves on the surface of water, so called because the restoring force is gravity. The article is about gravitational waves.
  3. Standard member sonhouse
    Fast and Curious
    19 Feb '16 11:50
    Originally posted by DeepThought
    The waves they are talking about come from the end of the inflationary era. At that time the radius of the universe was of the order of 1 metre. They would be powered by the inflaton field going into its ground state. The subsequent expansion is just coasting and since the gravitational waves have a wavelength of the order of the size of the early uni ...[text shortened]... er, so called because the restoring force is gravity. The article is about gravitational waves.
    I thought gravity waves was a stretching and compressing force like squeezing a tennis ball and letting go, something like that. The piece says the gravity waves coming out of the BB would now be something like the size of the universe even though they were cm's or meters wide when first created.

    The recent measurement of those 2 black holes colliding released two or three star masses converted directly to gravitational radiation resulting in waves we could measure 1.3 billion years later and 1.3 billion light years away. Don't know how they figured the masses of each but it would have been small compared to all the energy in the universe compressed into a small volume and THAT converted to gravity waves, that would have had to have been enormously more energetic than the two black holes colliding. Of course whatever that energy was, say when it was a cm across is now 27 odd billion light years across so that energy would be not very dense now compared to when it was generated.

    One thing I wondered, suppose you had been near the two black holes when they collided, outside the event horizon so you could perhaps live to tell about it, but how strong would the gravity waves have been close to the black hole's collision?

    Seems to me it would have been traumatic if not fatal. Or not, not sure.
  4. 19 Feb '16 12:56
    Originally posted by sonhouse
    http://phys.org/news/2016-02-gravitational-glimpse-ripples-big.html

    I got to thinking. If there is a huge amount of energy expended to make these gravity waves the size of the universe, could that alone explain the expansion noted from about 5 billion years ago?
    I asked in the other thread whether or not gravity waves could be 'dark energy' given that they clearly do store a massive amount of energy and until recently have been 'dark'.
  5. Standard member DeepThought
    Losing the Thread
    19 Feb '16 12:57 / 2 edits
    Originally posted by sonhouse
    I thought gravity waves was a stretching and compressing force like squeezing a tennis ball and letting go, something like that. The piece says the gravity waves coming out of the BB would now be something like the size of the universe even though they were cm's or meters wide when first created.

    The recent measurement of those 2 black holes colliding r ...[text shortened]... k hole's collision?

    Seems to me it would have been traumatic if not fatal. Or not, not sure.
    The article said that the central value for the combined mass of the resultant black holes was 62 solar masses and the progenitor black holes 36 and 29 solar masses. The observed strain was of the order of 10^-21. Applying the inverse square law to 1.3 billion light years means that at 1 light minute's distance from the merger the peak strain would have been of the order of 470 million; at 1 light hour the strain would be 130,000. My calculation is naive though - the inverse square law won't apply close to the merging black holes. Nevertheless, I think it's safe to say that that is not something you'd want to be near to.

    I got the figures from this Wikipedia page:
    https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves
  6. Standard member DeepThought
    Losing the Thread
    19 Feb '16 13:02
    Originally posted by twhitehead
    I asked in the other thread whether or not gravity waves could be 'dark energy' given that they clearly do store a massive amount of energy and until recently have been 'dark'.
    They'd need to behave like a negative pressure gas to have the right properties.
  7. 19 Feb '16 13:05
    Originally posted by DeepThought
    They'd need to behave like a negative pressure gas to have the right properties.
    I thought they just had to be energy.
  8. Standard member DeepThought
    Losing the Thread
    19 Feb '16 20:07
    Originally posted by twhitehead
    I thought they just had to be energy.
    Mass is energy. It's probably easiest if you look at this link:

    https://en.wikipedia.org/wiki/Dark_energy#Theories_of_explanation
  9. Subscriber joe shmo
    Strange Egg
    20 Feb '16 15:55 / 1 edit
    Originally posted by DeepThought
    The article said that the central value for the combined mass of the resultant black holes was 62 solar masses and the progenitor black holes 36 and 29 solar masses. The observed strain was of the order of 10^-21. Applying the inverse square law to 1.3 billion light years means that at 1 light minute's distance from the merger the peak strain would hav ...[text shortened]... rom this Wikipedia page:
    https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves
    So intense gravitational waves in space-time would be "felt"? That is our bodies and our time would compress or stretch as the wave passed? Are 3D bodies (we) represented as a region of the space -time surface? I also suspect that a fifth dimensional object floating on space-time would just bob up and down as the wave passed without compressing/stretching; much in the way we would bob in the ocean as a hydraulic wave passes?
  10. Standard member sonhouse
    Fast and Curious
    22 Feb '16 12:38
    Originally posted by joe shmo
    So intense gravitational waves in space-time would be "felt"? That is our bodies and our time would compress or stretch as the wave passed? Are 3D bodies (we) represented as a region of the space -time surface? I also suspect that a fifth dimensional object floating on space-time would just bob up and down as the wave passed without compressing/stretching; much in the way we would bob in the ocean as a hydraulic wave passes?
    In the interferometer laser detector at LIGO actually detects real movement of photons through a flight path of a few Km which results in a small phase shift between two separate optical paths. It is literally squeezing space and matter has to come along for the ride.

    I was imagining what it would have been like to be relatively close to that binary black hole that collapsed into one and they said the energy equivalent of 2 or 3 whole suns went into that gravity wave.

    If you were close, you probably would have been ripped apart I imagine, by the force of the waves.