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Topic: Premordial Gravity Wave
Message: Posted by: Daryl -the other brother (Apr 11, 2014 09:13AM)
On last nights episode of "The Big Bang Theory" the gang was excited about the recent discovery of the primordial gravity wave saying it could be the greatest scientific discovery of our lifetime. Having never heard of this wave I did a google search and found this is a real discovery (though not yet verified).

It has something to do with ripples in space time caused by the big bang and once verified, it could lead to a noble prize and open the door to a new era in physics.

Can any of our science gurus shed a little light on this?
Message: Posted by: MobilityBundle (Apr 11, 2014 01:44PM)
I'll try:

1. "General Relativity" (GR) is the branch of physics that deals with gravity on large scales, like cosmic scales. It was first developed in the early 1900's by Einstein and colleagues, and experienced a bit of a "golden age" in the 1960's and 1970's, when a lot of progress was made. One of the weird tenants of GR is that space and time are, for lack of a better word, physical things. That's in contrast to the Newtonian view (also the plain ole' intuitive view) that space and time are merely the backdrop through which physical things move. In other words, [i]otherwise empty[/i] space and time can wiggle, bend, etc. In a mathematically precise way, mass causes space to curve. [i]Moving[/i] mass causes space to continually change its curvature. And that's what a gravity wave is: it's the ripples of changing curvature one gets when one moves mass around.

2. Problem is, direct observation of this change in curvature is [i]really hard[/i]. That's because the effects are essentially minuscule: like water waves, the "strength" of a gravity wave decreases as the distance from its source increases. We're pretty far away from really heavy stuff like black holes or neutron stars moving around. (That's good news for the survival of our species, but bad news for detecting gravity waves.) Just to give an idea of the scale of things involved, early efforts to detect gravity waves involved setting up giant bars of aluminum about 2 meters long and 1 meter in diameter. If a gravity wave passed through, it would change the length of the bar... by roughly the amount of an atomic radius. So these bars had to be fabricated and monitored with [i]extreme[/i] precision. Some early claims were made to have directly detected gravity waves, but they were inconclusive.

3. Gravity waves also muck with light. This is a little technical to explain carefully, so I'll just gloss over some details. :) The upshot is that light has a "phase." Phase is invisible to the human eye, but it's a relatively simple property to detect with instruments. You can think of phase as a little clock that rides along with a ray of light, and it spins at some rate that depends on the medium through which the light is moving. For example, when light is shot out of, say, a laser, the "phase" of the beam just as it leaves the laser is pointing at 12:00. After it travels, say, one meter through air, the phase might be pointing at 3:00. After the same beam travels another meter through air, the phase would point at 6:00. In other words, the phase changes 90 degrees per meter through air. But it might change, say, 70 degrees per meter through glass, or 92 degrees per meter through a vacuum. (To be sure, I'm just making these numbers up to illustrate the concept; no idea if they're correct.)

4. Shift gears: now, talk about the big bang. For reasons I won't get into, the big bang theory calls for a period of what's called "inflation" to have happened right after the big bang itself. "Inflation" refers to a super-rapid expansion of [i]spacetime itself[/i] (and not just the stuff in spacetime). We obviously can't directly observe this part of the universe any more, but we do have a hint. There's what's called the Cosmic Microwave Background Radiation (CMBR), which is roughly speaking the "afterglow" from the big bang. More concretely, if you point a telescope in any direction -- even in otherwise empty space -- you'll get this low "hum" of light that doesn't seem to come from any source. That's the CMBR.

5. The CMBR encodes some information about the early universe. What they've done was carefully map the phases of the CMBR across the sky. If there were no inflation, the phases would expect to vary at, say, 92 degrees per meter... just light passing through a plain ole' vacuum. But apparently the phases change at a different rate, and it's (apparently) precisely the same rate that one would expect from the theory of inflation. So... break out the champagne. :)

Hope that's clear... at least somewhat. Glad to elaborate on anything that needs it...
Message: Posted by: Mehtas (Apr 11, 2014 01:53PM)
Any chance this technology can help find the missing malaysian plane ??
Message: Posted by: George Ledo (Apr 11, 2014 01:59PM)
Not to derail the thread, but I just rememberd something that I've been wondering about for years but never got around to looking up...

The universe, as far as we know, is expanding. If you (can somehow) chart the direction a bunch of galaxies are moving, is it possible to get an idea of whereabouts the big bang took place? Or is this old news?
Message: Posted by: Dougini (Apr 11, 2014 03:06PM)
Gravity is a strange thing. It is not a force, as was thought. It is a RESULT. Put a bowling ball on a soft bed. Try and roll a marble on the bed. It will travel around the "well" made by the ball, in toward it. That is a 3-D rendition of the effect.

But we are talking a 4th Dimensional Curve! [i]Time[/i] is also involved. The greater the mass, the greater and steeper the curve. Thus the apparent acceleration or "attraction". Also consider magnetism. Is this just a smaller form of gravity? Yes and no. I don't have my astrophysics professor friend here to explain it.

Gravity has an "A" wave and a "B" wave. Consider the "B" wave to be the BIG gravity, planets and stars. The "A" wave is on a micro scale. Accessing and amplifying the "A" wave is what the big boys are working on right now. However, most of that info is classified out the Yin Yang! :rolleyes:

Doug
Message: Posted by: MobilityBundle (Apr 11, 2014 04:49PM)
[quote]
On Apr 11, 2014, George Ledo wrote:
Not to derail the thread, but I just rememberd something that I've been wondering about for years but never got around to looking up...

The universe, as far as we know, is expanding. If you (can somehow) chart the direction a bunch of galaxies are moving, is it possible to get an idea of whereabouts the big bang took place? Or is this old news?
[/quote]
It's not a bad exercise to "rewind" the presently observed expansion. That tells us stuff.

But it won't tell us where the big bang occurred. It's not expansion in that sense.

The expansion of the universe is more akin to the expansion of a balloon. If you took a balloon and drew a bunch of dots on its surface, then started inflating, you'd find all the dots move away from all the other dots. But there's not a location [i]on the surface of the balloon[/i] where all the dots emanated from. Back in terms of the universe, it's possible to construct a mathematical picture in which the big bang happens at a certain point, but that point isn't anywhere in the current snapshot of universe.

That balloon example is often repeated in non-technical books, but I still think it's a little misleading. I wonder whether a better analogy is with monetary inflation. In that analogy, assume that we printed money once, a long time ago -- that event being analogous to the big bang. It can be possible that a long time ago, $1 bought you a large tract of land, whereas now $1 only buys you a can of coke. But that doesn't mean one can trace all the currently-existing dollars back to a "first dollar."
Message: Posted by: MobilityBundle (Apr 11, 2014 05:00PM)
[quote]
On Apr 11, 2014, Dougini wrote:
Gravity is a strange thing. It is not a force, as was thought. It is a RESULT. Put a bowling ball on a soft bed. Try and roll a marble on the bed. It will travel around the "well" made by the ball, in toward it. That is a 3-D rendition of the effect.

But we are talking a 4th Dimensional Curve! [i]Time[/i] is also involved. The greater the mass, the greater and steeper the curve. Thus the apparent acceleration or "attraction". Also consider magnetism. Is this just a smaller form of gravity? Yes and no. I don't have my astrophysics professor friend here to explain it.

Gravity has an "A" wave and a "B" wave. Consider the "B" wave to be the BIG gravity, planets and stars. The "A" wave is on a micro scale. Accessing and amplifying the "A" wave is what the big boys are working on right now. However, most of that info is classified out the Yin Yang! :rolleyes:

Doug
[/quote]
Fortunately, you DO have your [kinda] astrophysicist friend here to explain it -- me! :) (Okay okay, by way of full disclosure: I was a physics/math major in college, and I went on to get a master's degree in math. But my area of interest was, roughly speaking, in the mathematical foundations of quantum mechanics and general relativity. This is solidly in my wheelhouse.)

A few things:

1. A maxim that scientists often keep in the back of their minds is, "the map is not the territory." In that maxim, the "territory" is how the universe really behaves, and the "map" is how we describe it -- laws, abstractions, equations, etc. In other words, for all the universe cares, there's no such thing as momentum, or electric charge, or whatever. These are all abstractions that we use to describe how the universe works. Happily, they seem to be pretty useful.

But the idea of "force" is another such abstraction. It's not quite right to say "gravity is not a force, it's a result." In Newtonian physics -- which works perfectly well in a lot of cases -- gravity is a force. In general relativity, it's not a force. The difference is philosophically significant, and maybe it tells us about how different groups of people view the universe. But it doesn't tell us anything about gravity itself.

2. As for the "A waves and B waves," perhaps you're talking about E modes and B modes. Without getting into the details, those are descriptions that apply to any spatially-varying data. They don't necessarily have anything to do directly with gravity. (And it has nothing to do with "big" variations and "small" variations.) In technical language, the big news is that they recently discovered B modes in the CMBR, whereas they only previously saw E modes. The big bang theory (... and inflation, in particular) predicts the existence of B modes.
Message: Posted by: Daryl -the other brother (Apr 11, 2014 05:42PM)
[quote]
On Apr 11, 2014, MobilityBundle wrote:
But apparently the phases change at a different rate, and it's (apparently) precisely the same rate that one would expect from the theory of inflation. [/quote]

So would it be correct to say that what we "discovered" was that our way of thinking seems to be on the right path?
Message: Posted by: Cliffg37 (Apr 11, 2014 05:57PM)
Today we know exactly where the big bang happened. Describing that spot is very difficult. We can measure the motions of several galaxies, and then reverse extrapolate to where the event started. I think there is little significance to the exact spot, but it is there.
Message: Posted by: Cliffg37 (Apr 11, 2014 05:59PM)
Mobility... I do remember reading that scientists found it to great rejoicing, and then realized, it has no real meaning to us anymore.
Message: Posted by: TonyB2009 (Apr 11, 2014 06:06PM)
MobilityBundle, thanks for putting that so clearly. Fascinating. As a man who walked away from physics two decades ago, I am missing all the good stuff!
Message: Posted by: MobilityBundle (Apr 12, 2014 01:59AM)
[quote]
On Apr 11, 2014, Daryl -the other brother wrote:

So would it be correct to say that what we "discovered" was that our way of thinking seems to be on the right path?
[/quote]
Yup.

But it's not as anti-climactic as it sounds. The inflation hypothesis might appear to be a little bit far-fetched: it says that, for some unknown reason, for just the briefest of time periods after the big bang, the universe underwent this totally crazy expansion, where its volume increased by a factor of like 10^80, in a time period of like 10^-30 seconds. (I don't remember the actual numbers, but those are roughly the scales of things.) And of course, after that brief initial expansion, we never saw anything like that again. So the hypothesis may seem a little bit like "magic beans": it's an explanation for why things are they way they are, but the explanation raises a lot more questions than it answers.

The inflation hypothesis has gained some acceptance over the years, but I think that's more about the lack of good alternatives, rather than any experimental verification.

Until now, that is. This is the most direct evidence of inflation we've seen to date. And I believe (but I'm not 100% sure) that these "B modes" are the first experimental observation that was [i]predicted[/i] by inflation, that we didn't know beforehand.
Message: Posted by: MobilityBundle (Apr 12, 2014 02:06AM)
[quote]
On Apr 11, 2014, Cliffg37 wrote:
Mobility... I do remember reading that scientists found it [the "source" of the big bang] to great rejoicing, and then realized, it has no real meaning to us anymore.
[/quote]
That's not consistent with my understanding. See, for example:

http://curious.astro.cornell.edu/question.php?number=71

(This is another good explanation that doesn't use the "expanding balloon" analogy.)

If you remember where you read the article you're thinking of, I'd be curious to see it.
Message: Posted by: MobilityBundle (Apr 12, 2014 02:07AM)
[quote]
On Apr 11, 2014, TonyB2009 wrote:
MobilityBundle, thanks for putting that so clearly. Fascinating. As a man who walked away from physics two decades ago, I am missing all the good stuff!
[/quote]
Ain't that how it always works? As soon as you leave, things get good. :)
Message: Posted by: Cliffg37 (Apr 12, 2014 04:10PM)
I don't remember, but I just had brunch with a high ranking Physics/Astromomy professor at our local college. He was very happy to tell me that, Yes, the location has been pinpointed, and that it is everywhere. That sure puzzled me. If you use the balloon analogy (and I have in my own class) it is very obvious that the origin is somewhere in the center of the balloon. Not on the skin of the balloon as we are, but somewhere in the air inside. He countered with if we are on the balloon, every where else seems to be moving away and therefore WE are the center and the point of the big bang. Unless we go somewhere else, and then WE are at the center point there.

Truthfully it left me confused more than anything else. I am thinking I must have mis-interpreted that article I read. SO lets chalk that one up as my misunderstanding and be done with it there. I bow to your (excellent by the way) explanation. At least until I get a better understanding.
Message: Posted by: Daryl -the other brother (Apr 12, 2014 09:17PM)
Thanks MB, that helps a lot.
Message: Posted by: MobilityBundle (Apr 13, 2014 10:28PM)
[quote]On Apr 12, 2014, Cliffg37 wrote:
I don't remember, but I just had brunch with a high ranking Physics/Astromomy professor at our local college. He was very happy to tell me that, Yes, the location has been pinpointed, and that it is everywhere. That sure puzzled me. If you use the balloon analogy (and I have in my own class) it is very obvious that the origin is somewhere in the center of the balloon. Not on the skin of the balloon as we are, but somewhere in the air inside. He countered with if we are on the balloon, every where else seems to be moving away and therefore WE are the center and the point of the big bang. Unless we go somewhere else, and then WE are at the center point there.

Truthfully it left me confused more than anything else. I am thinking I must have mis-interpreted that article I read. SO lets chalk that one up as my misunderstanding and be done with it there. I bow to your (excellent by the way) explanation. At least until I get a better understanding. [/quote]

I think I see what's going on.

There are at least two distinct notions of what the "center" of the big bang could be. The first definition is what your brunch companion seems to have been working from: a point from which the rest of space is receding. The second definition is the metaphorical "center of the balloon." I understood your question to refer to the center of the balloon, but I think your friend understood it to mean the first thing. (And, of course, with that understanding his answer makes perfect sense... every point is receding away from every other point. That's still consistent with the balloon analogy: every point on the [i]surface[/i] of the balloon is indeed receding away from every other point on the surface.)

This might be a little technical, but for what it's worth, the metaphorical center of the balloon isn't that interesting from a physics point of view, because it has no physical significance. (At least, not that I can tell.) What I mean is, our universe has certain properties, and we really want to know those properties. And, in the name of learning about those properties, we an imagine the universe as sitting inside some higher-dimensional space (just like we can imagine the 2D surface of a balloon sitting inside a 3D space). But there's no physically-preferred way to [i]put[/i] the universe inside the higher dimensional space. So, one embedding might put the center of the metaphorical balloon at such-and-such coordinates, while another embedding might put the center of the balloon at other coordinates.

By way of example, suppose the universe was really simple: say, it's a 1 dimensional closed curve. We want to know stuff about the universe's geometry, like its total circumference or its curvature in this or that point. We might even find it useful to represent the universe as sitting inside a 3D space, using some formula that takes the point t in the universe and maps it to the point [f(t), g(t), h(t)] for some fancy functions f, g, and h. But we could have just as easily used the formula [1+f(t), 2+g(t), 3+h(t)], and we'd have the exact same geometry. The universe would be located in a different place in our abstract 3D space, but it'd have the same geometry. (And if one's understanding of physics is that the universe's geometry completely determines its physics, then you wouldn't care about the location in 3D space.)

As I re-read what I just wrote, I hope it's not too muddled. But in any case, thanks for the kind words (... you too, Daryl!) :)
Message: Posted by: Dougini (Apr 14, 2014 10:52AM)
MobilityBundle, you are extremely knowledgeable on this! Funny thing about Gravity, is, our universe cannot "control" it. The Black Hole for example. Beyond the Event Horizon, everything is crushed to a One-Dimensional point called The Singularity.

That is where you have infinite curvature and infinite density. Those concepts are so beyond us, I doubt we will ever fully understand it. Without referring to mathematical equations, that is. The star in question has to be something like 3.4 solar masses or more (I think).

When the star has collapsed to the point where all its mass has no more room to compress, or in other words there is no more "space" between atoms, Gravity is relentless. There is still too much mass, and the whole think winks out of existence. Oh, but that is just as it "appears"! Our laws of physics end at that time.

How many of these "holes" in space are there? Countless. They not only distort space, but make it impossible to draw a straight line past them. It all ends up in the Singularity. That is why linear interstellar space travel is impossible. You WILL eventually wind up in a Black Hole.

Fascinating discussion, guys! :)

Doug
Message: Posted by: Cliffg37 (Apr 14, 2014 11:17AM)
BTW my favorite use of gravity is the "Gravity lens" First suggest by the work of Albert Einstein, we can use the measurable gravity of a nearby star to gauge the distortion of the light from a farther star and therefore "see" and learn about the farther one.
Message: Posted by: tommy (Apr 14, 2014 12:41PM)
Nature is not a straight line. I would be more surprised if they discovered gravity was not wavy.
Message: Posted by: MobilityBundle (Apr 14, 2014 05:06PM)
[quote]On Apr 14, 2014, tommy wrote:
Nature is not a straight line. I would be more surprised if they discovered gravity was not wavy. [/quote]

Yeah, but the headline isn't "gravity is wavy." We've suspected that for many years. The real headline is that there's finally observational evidence for cosmic inflation in the early universe. (Although, from what I understand, the evidence isn't incontrovertible and is still being mulled over by cosmologists.)

By analogy to water waves, the headline isn't that waves break on the beach. The headline is more like Christopher Columbus watching the waves on a beach in the Mediterranean, and from that information alone deducing the exact shape of America's coastline.

In fact, this is arguably [i]more[/i] impressive in some sense. After all, Columbus could get up and go to America if he wanted, but we can't travel back to 10^(-30) seconds after the big bang.