Space and The wonders/mysteries of The Universe

That's good to be excited. I just saw this as so inevitable that I can't get so worked up. I was surprised to find in Figgy's article that Einstein of all people dithered about gravity waves. Black holes I can understand being unsure of since they are an extreme case, but being unsure of gravity waves is tantamount to being unsure of the whole of General Relativity, which has predicted a number of new things and hasn't failed a single test. If gravity waves didn't exist the whole mathematical structure would come crashing down. So I just nod my head when I see the observations come in and say "about damn time".

Halfy,

What I meant by my comment is that predicting based on a theory/load of maths is different to actually seeing it happen. Like designing a new plane and doing all the tests... they still stick a test pilot in to see how it actually performs.

Now they know it can be measured, equipment will mature and eventually be used to test that things are behaving as expected rather than seeing a result that could possibly be due to something unexpected.

Yep.

Sorted then.

I've been thinking about why this is so exciting for me. I think there are 2 things going on.

First is the old echos of math-dude in me that has been trained to see the final proof of a theorem as a reason for much beer.  The other is the excitement of having a completely new data stream. From now own, there are more and more gravitational observatories recording every blip, squeak and pop in the universe. Then some of the best minds on earth will take these gravitational noises, they'll analyze, theorize, scratch their heads, and argue like children, and in the end we'll understand the universe in a way we can't even imagine now.

When the older Forumshirians were kids, only a handful of people on our planet paid any attention to radio static besides cursing it and trying to filter it out.  But some of those noises turned out to be "quasars" which have told us much of what we now know about distant galaxies, or "pulsars" (which were first suspected to be alien civilizations ) which turned out to be a class of neutron star that's given us a lot of our theory of how stars die, black holes and such.  

Now with the new gravity noises, a whole new generation of astrophysicists will have a reason to get drunk and party!
           

I hope progress on this will be faster than I expect. The use of multiple mirror reflections suggests that it will come down to more than just making bigger instruments, so the progress may not be so slow and incremental. What would be really interesting is if a clear dark matter signal comes out of this.

halfwise wrote: What would be really interesting is if a clear dark matter signal comes out of this.

I'll drink to that!

could gravity waves be connected to dark energy?

Nobody knows. We know jackshit about dark energy except that we need something to explain the accelerating expansion of the universe.

Mrs Figg wrote:could gravity waves be connected to dark energy?

Yeah, as Halfy said, that's one of those fascinating unknowns. One of the tricky bits about energy is that the only ways we know to observe or measure it have to do with how it affects matter. If gravity waves eventually provide more answers into what's going on with the matter in the universe, that will presumably give insights into what's going on with the energy.

If you listened to the blip of "sound" that represented the gravity waves they captured you should have also been able to hear the background noise. The most interesting thing about the blip is that it was heard in two places at once which allowed them to prove they were actually measuring a real event. But there's a presumably a lot of information about gravitation hidden in that background noise too, just waiting for people to sort it all out. And that may have as much to do with computer algorithms as with the machine itself. Who can tell at this point what kind of gravitational snapshots are hidden in that hiss! What if dark matter is out there and moving in curious ways that can be "seen" by its gravity? What might that suggest about dark energy that's as yet unaccounted for? So much room for asking BIG QUESTIONS. Almost makes me wish I were a young grad student again!

so maybe Dark Matter may be some kind of strange star soup made out of a pinch of gravity and a pinch of black hole juice and a bunch of leftovers from the BB.

so let me get this straight, sorry if this sounds thick headed and dense of me, but have they found out what gravity is at last? this is probably obvious but I wasn't sure.

What I've been saying all along is that nothing new has been discovered.  They've only detected something which pretty much had to be there, it was just so hard to detect.  

We have a pretty complete understanding of gravity (okay, not on the quantum level but once you go there you almost have to give up what's meant by 'understand').   It's kinda like we always understood the oceans curved around the earth (typical gravity) and we knew there had to be waves there too (caused by water and gravity), but we couldn't see the waves before.

That's why I haven't been too excited, but Dave's excited because now we can see things we haven't seen before.  I should be excited, except it's tempered by the fact that this work has been 40 years in the making, and was made possible by incremental developments rather than major breakthroughs. What I feel is closer to satisfaction.

It's like we are back in the late 1500's polishing telescope lenses by hand: we finally got to the point where we can see real big things (like hey, there's ships on the water!), but it's still blurry.  Another 10 years of polishing the lens and we might begin to pick out masts.  So slowly and steadily more information will come in.  We always knew theoretically we should be able to magnify things with lenses, we just weren't good enough to make it work.  Now a whole new world is ready to see, it will just take more polishing.  And we all know how much was eventually revealed by telescopes.  

So far we've only seen things in gravity waves we thought had to be out there. We pretty much knew black holes existed and would spiral into merges, but it's exceedingly rare and so a great treat to capture it.  The surprise was in being lucky enough to capture a rare event, not so much in the event itself.   Surprises may come, but it will take time.

After edit: the analogy to lenses breaks down in that at that time, there was basically no theoretical understanding of light (the Arabs had figured it out about 100 years earlier, but it hadn't filtered to the Europe). So telescopic magnification was a big thing. Eyeglasses in Europe actually preceded the telescope by at least a century, but there wasn't enough theoretical understanding to predict one from the other.

With gravity waves the situation is very different. The theory was worked out around 1916. Einstein himself disavowed it briefly when one of his post-docs made an erroneous calculation that showed the waves shouldn't exist. An anonymous reviewer pointed out the error, and Einstein later accepted waves again. But he was the only one to have momentary doubts I suspect, for on a physical intuitive level from the warping of space-time (which is the basis of gravity) the waves must exist.

Mrs Figg wrote:so let me get this straight, sorry if this sounds thick headed and dense of me, but have they found out what gravity is at last? this is probably obvious but I wasn't sure.

Nothing dense about it. It's just a many-layered problem like pealing an onion, so there's probably never an "at last".  It just keeps going.

When a newborn colt first struggles up to its feet it gets its first lessons in gravity, and by the time grows up it has learned all it needs to know about gravity.

A ball player or archer has a very sophisticated understanding of gravity and the arcs that an object in flight will choose to take. It's amazing the instantaneous calculations that the brain can make to shoot a moving target. That's all he needs to understand about gravity. One more layer of the onion pealed.

When Sir Isaac Newton wanted to explain why the moon goes around the earth, or the earth around the sun, he came up with the words and formulas that allowed his insights to be taught to new generations of students.  That pealed another layer, and really is more than enough understanding for 99.9% of us for our whole lives.

Albert Einstein wanted to figure out what light and gravity might have in common, and though he never quite made it, he came up with some brilliant insights and the words and formulas that allow them to be taught to less inspired nerds like Halfy and me. This brings us to our current understanding, which is way more than 99.99% need to know about gravity.

Now after many decades of looking we've got a new tool that may in our lifetime allow us to peal one more layer off the onion and learn more than 99.999% of us ever need to know about gravity.

But there's no "at last" and I hope there never is. That would be sooooo boring!  

To take Dave's statement 1 step further, we know where the improvements in understanding will likely be, but we've been banging heads against it for decades without getting anywhere.

Since the 1920's we've had quantum mechanics which works really well with small things, and general relativity which works really well with big things. But gravity is too weak for us to measure with small things, so couldn't make progress.

Since the 1970's quantum mechanics was improved with our final versions of field theory, which means EVERYTHING we could measure on the small scale fit perfectly, just like with gravity EVERYTHING we could measure on the large scale fit perfectly.

Problem was, they were completely different theories. Gravity deals with smooth geometry, quantum mechanics deals with quantum chunks. Einstein originally came up with his theory of gravity while trying to understand light, as David said; yet light is described by the quantum theory. He spent most of his life trying reconcile the two, with no success. The closest anybody has come to success recently is string theory, which looks like it should work, but nobody has managed to work out anything that can be tested.

In the meantime, dark matter and dark energy came along. Nobody has gotten any traction in explaining them. Everybody has a gut feeling the unification of gravity and quantum mechanics may be behind one or both of them simply because theoretically that was the only missing element. But they may come from something completely new and the universe may end up being more complex once we understand them, not less complex via finally linking up quantum mechanics and gravity.

Where do gravity waves fit in? Historically light was related to quantum mechanics via the wave behavior. By finally observing gravity waves we may be closer to quantizing them. I dunno. There hasn't been any ground breaking progress in physics in 40 years, only unexplained observations and unobservable theory. If the two come together in my lifetime, every person I see that day gets a drink on me...I'm talking within eyesight and hollering distance clear up and down the block.

But full disclosure: I still only halfway understand the physics of the 70's, and don't at all understand the theory since then. I can't speak to the quality of the astronomical observations either. I'll just have the satisfaction of knowing that somebody in the human race finally gets it.

But full disclosure: I still only halfway understand the physics of the 70's, and don't at all understand the theory since then. I can't speak to the quality of the astronomical observations either. I'll just have the satisfaction of knowing that somebody in the human race finally gets it.

Me too. I was regularly around people who really did understand this stuff up till about 1990, and I still like to try to follow the developments as they come in, but without people to talk me through the finer points of these things I tend to get lost pretty fast. I sometimes look back at old notes that are clearly in my own handwriting, but I can't make heads or tails of them now. Like you, I'm quite happy just to know that SOMEBODY is getting it.

so is that a 'yes' then? or a definate maybe... have they detected that stuff that makes apples bounce on peoples heads? in slightly exasperating laymans terms?.

Gravity waves are not needed to make apples fall on heads.  Most of the effects of gravity can be explained without waves.  Let me try to break down the general relativity theory of gravity, maybe that will help.

Out in space, things will go in straight lines at constant speed, unless gravity makes them curve or change speed.  Typically we'd say a force is needed to make things change speed or direction.  Newton had demonstrated that a force that is proportional to mass and inversely proportional to distance squared will cause things to behave exactly as observed.  This was the theory of gravity, and it showed how to calculate things...and that was all the explanation we had for over 200 years.  People tried to "explain" it by various things like particles shooting around etc, but nothing completely served as a mechanism, and the math didn't care and worked perfectly so most people felt that was good enough.

Then Einstein for reasons I won't go into felt he could explain gravity as the curvature of space: things go in straight lines unless mass causes space to curve, thus causing motion not to go straight.  If you think of space with no mass as a rubber sheet with a grid drawn on it, if you roll a marble across the rubber it will go straight.  Now put a weight on the rubber sheet, it will pull down and distort the grid, and marbles will not roll straight across.  There's some subtleties involved in how exactly you calculate the motion, but basically when mass changes the grid it causes changes in the motion of other mass (and not just mass, light as well!), and that's the effect of gravity.  Things no longer just roll across.

It's a very simple visual model that explains gravity in terms of changes in space and time, and you can't get more fundamental than that!  It also explains some subtle differences from Newton's law of gravitation that people had been observing, and allowed predictions like bending of light which people hadn't seen, but were later confirmed.

One of those predictions were gravitational waves.  Normally when you think of the effects of gravity you think of a big stationary mass causing small masses to change their motion around the big mass.   But what if you have a couple big masses?  Then they will go oscillating back and forth as they orbit each other, causing changes in the rubber sheet of space.  But can these changes happen instantly?  If you are light years away and that mass far away changes position, will the rubber sheet where you are change instantly?  You know from experience what will happen from wiggling the end of a long rubber hose:...the change will move as a wave in the sheet, a gravity wave carrying the change in shape from the shifting mass to you!

So the gravity wave just propagates changes in the field of gravity.  Normally big masses aren't changing their motion fast enough for us to notice the waves.  But the waves are not gravity: the curvature of the surface is gravity, and it doesn't need a wave to be curved.

Going back to my earlier analogy, it's as if the curvature of the ocean represents the gravity of earth (the surface of the water is the surface of the rubber sheet - far from a perfect analogy but it will do).  If some mass below part of the ocean suddenly moved, a wave at that point would be produced and would travel away.  That wave has curvature in it that carries the force of gravity, but the oceans would still be curved without the wave.  You can have gravity without gravity waves; but knowing how gravity relates to curvature, you know that gravity waves must be possible.  It's just a matter of detecting them.

So imagine you are a thousand miles from earth.  You would see the curvature of the oceans, that's typical gravity.  You wouldn't see a wave unless you had a very good telescope, and then something set off a tsunami.  That wave is curvature in the water set off by a shifting mass.  The same behaviour of water used to describe how the oceans curve around the earth can be used to describe the waves.  You knew they had to be there, you just couldn't see them.

The curvature of the oceans show the effect of earth's mass.  The waves show the effect of changing that mass (this version of earth has no wind to cause the waves we are used to seeing).  The first effect is dominant and more common - that's normal gravity.

Mrs Figg wrote: have they detected that stuff that makes apples bounce on peoples heads? in slightly exasperating laymans terms?.

I'll try to be as exasperating as I can then.

When Sir Isaac took the apple to the head he didn't have any idea that the apple had vitamins in it, or that the gravity had waves in it.

He was perfectly correct in all his conclusions. It's just that we've kept looking closer and closer at both apples and gravity, and the closer we look the more we "discover" about them.

{{{{{{After reading this lot what I need is more buckie and a long lie down! Lucky Im not actually here I'd probably have a headache by now }}}}}}

but what I mean is, they didn't know what gravity was, even though it fit theories, and now they know its waves?

(((( )))))