Just read about the "L", still not understanding it completely. They shoot lasers down both arms, and if one comes back slightly later, that is what detects the gravitational wave. That confirms what measurement is, the difference. But still don't understand the complete how.

This is really complex stuff. I don't think we'll be able to understand it better than we already do, unless we start studying physics.

(February 12, 2016 at 9:44 am)Excited Penguin Wrote: This is really complex stuff. I don't think we'll be able to understand it better than we already do, unless we start studying physics.

I agree, but this isn't the same ignorance theists use. You don't have to be able to build a car to understand the general concept of a combustion engine to know it does not run on pixy dust, and you still can learn how to drive a car. I trust these experts because scientific method is the same idea from grade school science all the way up to Hawking. Follow steps, observe and test and falsify, hand your findings over to someone else independent to see if they come up with the same data.

Just the fucking fact they can detect that at such a tiny difference. Just wow!

(February 12, 2016 at 9:36 am)Brian37 Wrote: Just read about the "L", still not understanding it completely. They shoot lasers down both arms, and if one comes back slightly later, that is what detects the gravitational wave. That confirms what measurement is, the difference. But still don't understand the complete how.

Someone with more knowledge/smarts correct me if I'm wrong, but I'm'a try to come up with an interesting and informative analogy.

Imagine you're standing in the corner of a big box made of rubber.  (I know, I know, stay with me.)  You don't know exactly how big it is, so you take a ruler and, starting at your corner, mark off every foot on the wall with chalk.  You find out that the box is both 20 feet long and 20 feet wide, a perfect square, so there are 20 chalk marks on each wall.

You suspect that someone on the outside might be squeezing the box a little bit, distorting its shape by pressing or pulling on one of the walls.  You can't tell, though, because all you have to go on are the 20 chalk marks on the wall, and you're not fast or precise enough to measure if the box actually changes shape to say, 19 feet 11 inches by 20 feet 1 inch for just a second.

So, you devise a clever experiment.  Standing in your corner, you throw two tennis balls - one along the length (which you think is 20 feet) and one along the width (which you think is 20 feet).  You make sure the tennis balls are exactly the same, and you throw them at the exact same speed. 

Since they're both traveling at exactly the same speed, and presumably going the same distance, they should get back to you at exactly the same time.  However, one gets back to you a second later than the other one.  As far as you can tell, they both went exactly 40 feet (20 marks of chalk to the opposite wall, and 20 marks back).  However, the difference in time means that, indeed, someone must have been squeezing the box a little bit from the outside, making the one wall just a little farther than 20 feet away when the tennis ball hit it.


That was my best shot

(To clarify, the tennis balls are the lasers, throwing one along the width and one along the length is the "L" they're discussing, the room itself is... spacetime, the universe, etc, and the person pushing or pulling the room slightly... is gravity!)

I already understood that part. What I don't understand is how you can tell the difference in arrival time between the two beams of light.

(February 12, 2016 at 10:12 am)TheRealJoeFish Wrote:

(February 12, 2016 at 9:36 am)Brian37 Wrote: Just read about the "L", still not understanding it completely. They shoot lasers down both arms, and if one comes back slightly later, that is what detects the gravitational wave. That confirms what measurement is, the difference. But still don't understand the complete how.

Someone with more knowledge/smarts correct me if I'm wrong, but I'm'a try to come up with an interesting and informative analogy.

Imagine you're standing in the corner of a big box made of rubber.  (I know, I know, stay with me.)  You don't know exactly how big it is, so you take a ruler and, starting at your corner, mark off every foot on the wall with chalk.  You find out that the box is both 20 feet long and 20 feet wide, a perfect square, so there are 20 chalk marks on each wall.

You suspect that someone on the outside might be squeezing the box a little bit, distorting its shape by pressing or pulling on one of the walls.  You can't tell, though, because all you have to go on are the 20 chalk marks on the wall, and you're not fast or precise enough to measure if the box actually changes shape to say, 19 feet 11 inches by 20 feet 1 inch for just a second.

So, you devise a clever experiment.  Standing in your corner, you throw two tennis balls - one along the length (which you think is 20 feet) and one along the width (which you think is 20 feet).  You make sure the tennis balls are exactly the same, and you throw them at the exact same speed. 

Since they're both traveling at exactly the same speed, and presumably going the same distance, they should get back to you at exactly the same time.  However, one gets back to you a second later than the other one.  By your measurements, they both went exactly 40 feet (20 marks of chalk to the opposite wall, and 20 marks back).  However, the difference in time means that, indeed, someone must have been squeezing the box a little bit from the outside, making the one wall just a little farther than 20 feet away when the tennis ball hit it.


That was my best shot

Ok, that explains it better. I've have a laypersons understanding. Measuring is either done by bouncing or catching or both. But what really freaks me out in a good way, is how small that difference is 1,000 times smaller than the width of a proton! MOTHER FUCKER THAT IS PRECISE!

The "how" goes like this in a simplified version: you arrange the laser light waves coming back from the two arms to exactly cancel at the point back in the middle where your light sensor sits - the peaks of one exactly meet the troughs of the other and no laser light hits the sensor. If one arm gets slightly shorter or longer, one of the waves will be shifted ever so slightly because it had to travel further, the peaks don't quite meet the troughs of the other returning laser wave and the cancellation will not be perfect any more->light reaches the sensor and you see a signal.

The mathematically complex part is to properly understand why grav waves change the length of the arms as measured by a light wave.

@Aractus
always typing out "gravitational" on my phone gets too exhausting after a while

An old comic book cannot compare to this, ever.

The truly astonishing thing is not that a gravitational wave has been measured, but that Einstein worked out such counter-intuitive theories without the benefit of building on other's ideas (i.e. Newton's).