Slashdot Mirror

← Back to Stories (view on slashdot.org)

Why Gravity Is the Ultimate Space Telescope (forbes.com)

Posted by samzenpus on from the getting-the-best-look dept.

TheAlexKnapp writes: Ethan Siegel has written a nice overview of gravitational lensing, and how taking advantage of it has enabled to study parts of the universe that otherwise would've require the construction of massive telescopes. From his Forbes article: "Although the first gravitational lens wasn't discovered for some 40 years after it was first theorized, it's now the most prolific tool for weighing distant (foreground) galaxies, and discovering ultra-distant (background) galaxies. Although this isn't a technique we have precision control over — the Universe puts the lenses and the lensed objects where they are, and all we can do is watch — there's a spectacular amount of material that's out there."

42 comments

  1. The size of the universe fascinates me. by GoodNewsJimDotCom · · Score: 0

    I like that the stars are out there, bigger than our petty affairs down here on Earth. I also like to think that there are even more amazing than the stars we observe in this universe.

    --
    God spoke to me
  2. Research that gravity by Anonymous Coward · · Score: 0

    Interstellar

    01:04:10 CASE, you're with me. Anyone else can stay.

    01:04:13 If we are talking about a couple of years,

    01:04:15 I could use the time to research gravity,

    01:04:18 observations from the wormhole, that's gold to Professor Brand.

    01:04:20 TARS, factor an orbit around Gargantua, conserve fuel, minimize thrusting.

    Anyone know how many times they used that word?

    1. Re:Research that gravity by garyisabusyguy · · Score: 2

      Eff Interstellar, it's Intergalactic

      https://www.youtube.com/watch?...

      --
      Wherever You Go, There You Are
    2. Re:Research that gravity by sexconker · · Score: 1

      I knew what this was going to be before I clicked on it.
      I am satisfied.

    3. Re:Research that gravity by Anonymous Coward · · Score: 0

      Your favourite part is when she plunges her 12" dildo into your tight, pink little anus. Nothing quite like fucking a woman while she reams your ass, eh?

  3. Or not by lostinwilderness · · Score: 1

    Maybe it's just diffraction. http://www.thunderbolts.info/t...

    1. Re:Or not by Anonymous Coward · · Score: 0

      Diffraction is wavelength specific, as are refraction effects too, while gravitational lensing and bending of light has been observed to be wavelength independent in many situations.

    2. Re:Or not by Anonymous Coward · · Score: 0

      That "article" is a decade old. Lots more scientific evidence has been added since then. Also, telescopes have gotten larger since Einstein's time, which is part of the point of the Forbes article.

  4. Ultimate Space Telescope? by Anonymous Coward · · Score: 0

    I've been hearing this for ages about how gravitational lenses supposedly allow us to observe anything behind them with great detail, but I've never actually seen a single un-lensed image that would have proved this point. Has it actually been done or is this another one of those hypothetical concepts astronomers like amuse themselves with?

    1. Re:Ultimate Space Telescope? by Anonymous Coward · · Score: 0

      It has been proven conclusively through theory and observation.

    2. Re:Ultimate Space Telescope? by Anonymous Coward · · Score: 1

      I've been hearing this for ages about how gravitational lenses supposedly allow us to observe anything behind them with great detail, but I've never actually seen a single un-lensed image that would have proved this point.

      How would that prove the point? It is quite clear from the observations that galaxies spectroscopically matching ones far away are visible in greater angular resolution and with greater light gathering ability than those that are not gravitationally lensed. If you don't agree with the spectroscopic matching and other observations like star formation regions, etc., then "un-lensing" the image or not is not going to prove anything to you.

    3. Re: Ultimate Space Telescope? by Anonymous Coward · · Score: 0

      I suspect he/she means, "If the gravity lenses are fixed in space between us and the observed distant objects, how do we know what the objects look like without the lenses?"

  5. Used to be almost sci-fi ... by gstoddart · · Score: 3, Interesting

    Wow, years ago, as a fresh-scrubbed nerd hanging out with other nerds, gravitational lensing was as yet unproven; it was based in science, but I don't think anybody had done it yet.

    Of course, this was right around the time when we were on the cusp of seriously discussing exoplanets, yet to confirm a black hole, still working on hubble, and when radio astronomy was still coming into its own. Things which are almost commonplace were cutting edge stuff which hadn't happened yet.

    To all the physicists, astrophysicists, amateurs, and other people who have made space discovery so damned awesome for the last few decades ... you're fucking awesome, and thanks for showing us just how cool the universe is.

    --
    Lost at C:>. Found at C.
    1. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 1

      Of course, this was right around the time when we were on the cusp of seriously discussing exoplanets, yet to confirm a black hole, still working on hubble, and when radio astronomy was still coming into its own.

      Your sense of time seems a little wonky, since galactic gravitational lensing was late 70s (~60 years after Eddington's original observation using the Sun), radio astronomy was well established by the 60s (e.g. Arecibo was built in 1963), Hubble just got first approval of funds about the same time, and the first confirmed exoplanets was not until the 90s.

    2. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      It seems obvious that light is affected by gravity, yet for some reason gravitational lensing is attributed to bending space and time instead of the simpler, more obvious explanation that it is simply being pulled on by gravity which results in a change of direction.

      I suppose the bending of light between a crack in my fingers is because bending space time too.

    3. Re:Used to be almost sci-fi ... by Sique · · Score: 1

      Mathematically, both are the same. The gravitational pull causes exactly the same bend than the curved space time. General Relativity says that the gravitational pull you observe is a result of the curved spacetime.

      --
      .sig: Sique *sigh*
    4. Re:Used to be almost sci-fi ... by delt0r · · Score: 1

      General relativity results in 2x as much bending via gravity as classical theory IIRC (or is it half as much). So there is a difference.

      --
      If information wants to be free, why does my internet connection cost so much?
    5. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      yet for some reason gravitational lensing is attributed to bending space and time instead of the simpler, more obvious explanation that it is simply being pulled on by gravity which results in a change of direction.

      Umm, there is no difference, as an object in free fall and light both follow geodesics in GR, meaning they both go along something similar to the concept of a straight bath deflected by the shape of space time. You can think about it as force or bent space-time, and in the right limits, both you get Newtonian force for gravity. However light bending around the Sun, and even Mercury orbiting around the Sun, deviate from the Newtonian limit and require GR to get the numbers actually right.

      I suppose the bending of light between a crack in my fingers is because bending space time too.

      Does that quantitatively match GR? No, it doesn't even do wavelength-independent bending of light.

    6. Re:Used to be almost sci-fi ... by khallow · · Score: 1

      General relativity results in 2x as much bending via gravity as classical theory IIRC

      Not for us. The pull of gravity on humans is almost classical theory with the difference being barely detectable as a time dilation. And classical theory allows for gravity to pull on objects going faster than the speed of light while general relativity has no such objects.

    7. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      Classical theory doesn't predict any bending of light due to gravity because photons have no rest mass.

    8. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      Classical theory can predict an acceleration from F=ma=GmM/r^2, where in the limit of small m it cancels out fine to give: a=GM/r^2.

    9. Re:Used to be almost sci-fi ... by delt0r · · Score: 1

      You need relativity to claim that a photon has no rest mass. There is no such concept in newtonian only physics.

      --
      If information wants to be free, why does my internet connection cost so much?
    10. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      No you don't; the concept of massless particles predates relativity. Relativity is needed to show that gravity can interact with massless particles through their relativistic mass.

    11. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      The limit of small m in that formula is still a non-zero number, because classical gravity acts entirely through mass. It's assumed that the relatively small mass, m, is still a positive number. F=0 when m=0. "Massless" is not the same as "relatively small mass".

      This page describes early attempts to explain gravity bending light by classical methods, but your reasoning doesn't work.

    12. Re:Used to be almost sci-fi ... by delt0r · · Score: 1

      Err really no. Photons as packets of light predates very briefly. But e=mc2 *is* relativity, and without that there is no such thing as zero rest mass. That would just be zero mass in *all frames of reference*.

      --
      If information wants to be free, why does my internet connection cost so much?
    13. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      The corpuscular theory of light, which described weightless packets of light, was proposed by Newton. That predates relativity more than "very briefly".

      My original use of "rest mass", which is a relativistic concept, was poor, I'll admit. I should have just used "mass".

    14. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      All you need is for the mass to be very small, not zero, and gravity would behave the same on light in classical gravity as it would any other particle. Or you can even take a limit of m goes to zero, and still get a similar result. This is why Newtonian gravity was used to predict the deflection of light hundreds of years before relativity and was considered in part by Newton himself.

      The only case where the mass of light really comes into play is if you want to talk about gravity from the light pulling on something else, which was not considered seriously before the seeds of relativity.

    15. Re:Used to be almost sci-fi ... by Anonymous Coward · · Score: 0

      That page uses the exact same math, as m there the mass of the large gravitational object deflecting light. The mass of the light has been cancelled out to give a=M/r^2. It is the exact same logic, that the mass of light doesn't matter for the force on light and its equations of motion.

      "Massless" is not the same as "relatively small mass".

      And a limit of something going to zero is not the same as saying it is relatively small. Limits get used for purpose in calculating approximations, but that is not the case here. A limit of something going to zero is saying that it is infinitesimally small, which with real numbers amounts to being zero.

  6. ELI5 by Anonymous Coward · · Score: 0

    Is it possible to have double lensing?

    1. Re: ELI5 by Anonymous Coward · · Score: 0

      If one, then any, so yes.

  7. Imagine by romit_icarus · · Score: 2

    Now just imagine a Beowulf cluster of these gravitational lenses...

    1. Re:Imagine by Anonymous Coward · · Score: 0

      Wrong analogy. You should imagine an optical bench of them.

    2. Re:Imagine by Tablizer · · Score: 1

      imagine a Beowulf cluster of these gravitational lenses...

      Here ya go:
      http://apod.nasa.gov/apod/ap12...

      --
      Table-ized A.I.
  8. 40 yrs? by stud9920 · · Score: 2

    Although the first gravitational lens wasn't discovered for some 40 years after it was first theorized

    Eddington demonstrated gravitational lensing just a few years after the theory was published, in 1919. And he would possibly have been quicker if if weren't for WWI

  9. Because aperture is measured in galaxy diameters? by Anonymous Coward · · Score: 0

    How surprising.

  10. Ultimate? by Anonymous Coward · · Score: 0

    One huge flaw is that you can't point it where you want to look. But maybe that's not a major deal. I mean, it's not that they build telescopes that can be pointed at specific things anyway. All of them are fixed and pointing at some random location.

    1. Re:Ultimate? by KingOfBLASH · · Score: 1

      You don't need to look at a lens straight on to see through it. If that were the case, anyone wearing glasses who was not looking directly at you would be missing their eyes.

  11. FOCAL Mission by Maritz · · Score: 2

    Kinda surprised he'd write an entire article about what a great telescope gravity makes for and not mention the FOCAL proposal. If you had a probe sufficiently distant from the sun opposite Alpha Centari and there was a city full of little aliens there, you'd be able to see the cars move around in the streets. Not that this will ever happen or that humanity are capable of such projects - we clearly are not. But it's still a nice idea.

    --
    I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
    1. Re:FOCAL Mission by delt0r · · Score: 1

      FOCAL is in fact far more plausible than much of the outside of the box thinking. Solar sails can even get you out far enough from the sun. However i am a little suspicious of the diffraction limit claim. It is not really a big lense. Just approximately so, with a massive ball of 6000C plasma in the middle of the camera.

      --
      If information wants to be free, why does my internet connection cost so much?