Astrophysics and Cosmology - Discuss the Universe here

[Agent : Orange]

I was ignorant of Neil's personal encounter with Sagan and the inspiration it gave. As Zeebo said, I'm happy the Sagan information was presented in the first episode - because those few well timed moments were as unto the launching of a rocket.

I wasn't aware of his connection to Sagan either, and that sealed it for me.

[area51drone]

I thought he wasn't as good as Sagan, in as far as him being as passionate about the subject matter, but I still found it to be very good.   I really thought the visuals were amazing, and I too liked the story of his connection with Sagan.   I'll definitely watch the rest of them.

[Mind Flayer Monk]

Agent: Orange, could you give us your thoughts on this next week please:

http://www.theguardian.com/science/2014/mar/14/gravitational-waves-big-bang-universe-bicep

"Discovery of gravitational waves by Bicep telescope at south pole could give scientists insights into how universe was born"

"Rumours have been rife in the physics community about an announcement due on Monday from the Harvard-Smithsonian Center for Astrophysics. If there is evidence for gravitational waves, it would be a landmark discovery that would change the face of cosmology and particle physics."

[zeebo]

..."Discovery of gravitational waves by Bicep telescope at south pole..."

I think they're looking in the wrong place.  I'm sure I saw a grav wave in my coffee this morning.  I mean I'm almost sure of it.  Maybe I bumped it.

[Mind Flayer Monk]

I think they're looking in the wrong place.  I'm sure I saw a grav wave in my coffee this morning.  I mean I'm almost sure of it.  Maybe I bumped it.

Its like a Kurt Vonnegut novel.

[zeebo]

Its like a Kurt Vonnegut novel.

I sense a wampeter in the making.

[Camazotz Automat]

And so it goes.

[Agent : Orange]

Agent: Orange, could you give us your thoughts on this next week please:

http://www.theguardian.com/science/2014/mar/14/gravitational-waves-big-bang-universe-bicep

"Discovery of gravitational waves by Bicep telescope at south pole could give scientists insights into how universe was born"

"Rumours have been rife in the physics community about an announcement due on Monday from the Harvard-Smithsonian Center for Astrophysics. If there is evidence for gravitational waves, it would be a landmark discovery that would change the face of cosmology and particle physics."

There are a number of big problems in cosmology that have no easy solutions in the standard big bang model. Let me go through them here, and then give an explanation of why this story could be so significant.

What I'll call the "classic big bang" picture makes problems for astronomers and cosmologists in the following ways. First, we can point our telescopes out and observe the cosmic microwave background, the so-called "surface of last scattering" that marks when the density of cosmic matter dropped sufficiently for light to travel long distances without scattering. This radiation is a marker for the exact time that the universe transitioned from being opaque to transparent to electromagnetic radiation. The radiation is spread out over the whole sky. The afterglow of the big bang is still travelling through the universe and we can observe it. In fact, when you observe this radiation from one part of the sky and then turn your telescope in the exact opposite direction, the radiation you see has the same spectrum. This means the temperatures on both sides of the sky are identical to within a very small amount.

But the problem with this is that these patches of sky are too far apart to have interacted with one another since the speed of light is finite. They are just too far apart. These two opposite parts of the sky should never had enough time in contact with one another to thermalize. If the universe began to expand at the rate we see today as soon as it came into being then we would expect the matter within it to be lumpy and so the cosmic microwave background should be a mishmash of different temperatures over the whole sky. But it isn't. Why? This is called the horizon problem.

The second big problem is that the universe must have started in a very uniform state for clustering and structures to grow under the effect of gravity. It seems unnatural for this to be so. Why wouldn't the universe tend to start in a chaotic state, or at least something with more features to it? When I say very uniform I mean variations in the density from point to point that are minute with respect to the background so that the universe would produce a cosmic microwave background with such a uniform temperature. When we make measurements of the cosmic microwave background we find that the mass within the universe must add up to nearly the critical value to balance the expansion with the pull of gravity. This means the universe must have started out as geometrically very close to being flat. So why would the distribution of matter in the early universe be smoother than a cueball? This is called the flatness problem.

The modern big bang, which is now called "The Standard Model" of cosmology solves both of these problems in an ingenious way. This solution is called inflation.

Inflation says that before expansion began, the universe loitered in a hot dense state for long enough to thermalize, and then underwent a burst of extremely rapid expansion. This is very early on in the evolution (at a time much less than the first second of it's existence, something like 10^-32 second in fact). This burst of expansion blows the universe up to something like the size of a grapefruit from the size of a proton. Then the inflation stops and the normal expansion picks up from there. This small burst of superexpansion is enough to solve both cosmological problems. First, the horizon problem is solved because all parts of the universe are in causal contact which means information can be exchanged allowing the matter within to thermalize.

Then after it is blown up, the universe must have been extremely flat just by virtue of the inflationary expansion, just like an ant crawling on a balloon being blown up. The inflated balloon looks very flat to an ant because the radius of curvature becomes much larger than the scale of the ant. So regardless of how it starts out, inflation will *drive* the universe to be flat.

Both of these problems are solved naturally by inflation. This scenario is so satisfying and effective at solving these problems that most folks who study this stuff generally agree some form of early universe inflation must have occurred.

So far no conclusive traces of inflation have been found. However...

Inflation is known to magnify gravitational waves, and it's thought that these waves should have been running around the universe at very early times (less than 10^-32 so before inflation). During this time, the infant spacetime should have been ringing like a gong. In fact, the presence of these vibrations of spacetime should have left signs of their interactions in the cosmic microwave background.

Then inflation occurred, and the effects of these gravitational waves should be "frozen in" to the cosmic microwave background. This amounts to creating patterns in the background, which can be detected if you look at the polarization of the radiation. In the standard picture there are radial types of patterns which should be formed called E-modes and also a pattern that looks like a spiral called a B-mode.

These polarization modes have been observed. E-modes were first measured in 2003
http://www.nature.com/nature/journal/v420/n6917/abs/nature01269.html
and the B-modes detected last year.
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.141301

But Inflation says there should also be another kind of B-mode, a more rare and elusive type called a primordial B-mode. This polarization pattern is directly correlated to what space-time was doing all the way back to the moment of creation.

The announcement on Monday is rumored to be the detection of these primordial B-modes.

This would mean that some kind of inflation really did occur, and that our picture of the early universe is essentially complete, that at least we have the basics of the story right. It also proves that there are primordial gravitational waves such that a new window into the early universe is opened: we can only get electromagnetic radiation to the time the cosmic microwave background was released, when the universe was only about 300,000 years old. There is no similar restriction on gravitational waves, which can propagate from the origin of the universe on.

That's what's riding on Monday.

[Mind Flayer Monk]

Thank you Agent:Orange.

That entire post should go in the top right corner.

There was a show on a few years ago (the Universe?) where they did a neat analogy for inflation with a guy dropping a balloon filled with paint onto the ground.

and the B-modes detected last year.
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.141301

Oh a letters journal. Someone tried to get to publication one week earlier than the guy with better data.
So are you at McGill as well?

[UnscreenedCaller]

Awesome post, Agent: Orange

I read this over several times, and each time I felt an overwhelming sense of awe:

lation says that before expansion began, the universe loitered in a hot dense state for long enough to thermalize, and then underwent a burst of extremely rapid expansion. This is very early on in the evolution (at a time much less than the first second of it's existence, something like 10^-32 second in fact). This burst of expansion blows the universe up to something like the size of a grapefruit from the size of a proton. Then the inflation stops and the normal expansion picks up from there. This small burst of superexpansion is enough to solve both cosmological problems. First, the horizon problem is solved because all parts of the universe are in causal contact which means information can be exchanged allowing the matter within to thermalize.

I can't wrap my mind around such an event that makes any adjective inadequate.

[area51drone]

Agent, please answer this.  Is there a limit to the density of a gravitational singularity?   Does such a singularity, assuming it is not rotating, have any dimension?   

[zeebo]

Thank you Agent:Orange.

That entire post should go in the top right corner.
...

Agreed!

[zeebo]

Agent, please answer this.  Is there a limit to the density of a gravitational singularity?   Does such a singularity, assuming it is not rotating, have any dimension?

That's a great question.  I've wondered myself, if the singularity is like a point in geometry which is there but does not take up any actual space.

[Agent : Orange]

So are you at McGill as well?

Nope. But I know a few people there.

Agent, please answer this.  Is there a limit to the density of a gravitational singularity?   Does such a singularity, assuming it is not rotating, have any dimension?

That's a great question.  I've wondered myself, if the singularity is like a point in geometry which is there but does not take up any actual space.

That's an interesting question. Singularities are points where some function becomes infinite, like f(r)=1/r. In this simple example you have problems at r=0 which gives an infinite answer, but r+e is fine, where e is a number that can be as small as you want. So a singularity really is just like a point where some function (which could be mass or charge density) becomes infinite. Sometimes these singularities can be fixed by just changing your coordinate system. In general relativity at least there's a way of telling if a situation like the one above is a "real" singularity or just a "coordinate" singularity. All of the nasty ones (like the center of a black hole) are real singularities (ie curvature becomes infinite there). The easier ones to deal with (like the event horizon for a non-rotating black hole) can be taken out by a clever choice of coordinates and they're not real singularities (think of the north pole - the coordinates there are singular but theres nothing weird that happens to the actual Earth at that point). Once you start bringing in quantum mechanics these things become much more complicated. So I hope my simple answer helped you both!

[area51drone]

I'm trying to lead myself down a road here.    So there really is no physical dimension of all the mass that makes up the center of a black hole?   In other words, the center of a black hole is dimension-less?   And that point in space could contain all the mass/energy of the entire universe inside of it?

As you surmised where I might be going with this, how does the big bang theory (or black holes themselves) jive with quantum mechanic's rules about particles fitting into spaces smaller than their wavelength?

I don't know, something just seems wrong to me about the big bang theory.   It's not that I can't wrap my head around the idea, I understand why the scientific community believes the theory (in laymen terms anyway).   But no one can theorize what actually created the "bang" that released the energy in the first place, or have they?    If a black hole can suck in infinite mass/energy into a single, dimensionless point and not explode itself into its own crazy big bang universe,  I have to ask myself, W. T.  F....

[Agent : Orange]

I'm trying to lead myself down a road here.    So there really is no physical dimension of all the mass that makes up the center of a black hole?   In other words, the center of a black hole is dimension-less?   And that point in space could contain all the mass/energy of the entire universe inside of it?

No, a black hole has the mass of the star that formed it, not an infinite mass.

As you surmised where I might be going with this, how does the big bang theory (or black holes themselves) jive with quantum mechanic's rules about particles fitting into spaces smaller than their wavelength?

I don't know, something just seems wrong to me about the big bang theory.   It's not that I can't wrap my head around the idea, I understand why the scientific community believes the theory (in laymen terms anyway).   But no one can theorize what actually created the "bang" that released the energy in the first place, or have they?    If a black hole can suck in infinite mass/energy into a single, dimensionless point and not explode itself into its own crazy big bang universe,  I have to ask myself, W. T.  F....

Black holes and the big bang are two separate phenomena which are very different from one another. Both are similar in that they have infinite density in *classical* theories. But that doesn't mean much since it's probably true that quantum mechanics prevent singularities from forming at all in nature. As you say (and I mentioned earlier) the picture becomes more complicated when quantum mechanics is brought into the discussion. The best we can say is that classical theories break down when they predict singularities and that there is something that happens to them that comes about from quantum mechanics in a more complete picture. There is a whole body of work out there where people apply QM to black holes or other aspects of general relativity, which makes predictions like Hawking radiation and the Unruh effect for example. And there are a bunch of ideas about the nature of the big bang itself as well but none have conclusive evidence yet to back them up, meaning they're still a lot of speculation.

The conversation may be significantly more interesting tomorrow morning.

[Camazotz Automat]

Episode 2 of COSMOS : A Spacetime Odyssey.

Opposing appendages up. 

The last scene was ~wicked cool~, but I won't contaminate with elaboration.

Re-watched Ep.01 just prior. Enjoyed the replay even more due to analyzing it less while drinking a Christmas gift - something called WESTERN SON Texas Vodka - which allowed a more relaxed neural percolation.

By the end of Ep.01, I was fully on the bridge of the ship with Tyson just as Episode 2 aired.

[area51drone]

No, a black hole has the mass of the star that formed it, not an infinite mass.

And everything else it's sucked up, right?

[Agent : Orange]

And everything else it's sucked up, right?

There's no black hole that's been found with an infinite mass, they're all finite, event the supermassive ones at the center of quasars can be inferred to have masses like a billion times the mass of the Sun. Black holes are not necessarily accreting matter continuously. An infinite mass would mean the event horizon is infinitely large.

Maybe a subtle point but an important distinction.

[area51drone]

There's no black hole that's been found with an infinite mass, they're all finite, event the supermassive ones at the center of quasars can be inferred to have masses like a billion times the mass of the Sun. Black holes are not necessarily accreting matter continuously. An infinite mass would mean the event horizon is infinitely large.

Maybe a subtle point but an important distinction.

No, it's definitely a good point.   Obviously not all black holes are still sucking stuff up.   So let me get this straight then - a  black hole is not really a single point in which mass/energy cannot escape (except with maybe Hawking radiation)?   Is that correct?   So if that's true, then the mass of the black hole is actually smeared around the cone, and the black hole actually has a real dimension?

I always thought that the mass of a (non rotating) black hole was actually at the singularity, and the event horizon was just a "point of no escape" and not necessarily a "boundary of matter."   Meaning, let's say the event horizon of a very old non accreting SMBH is 10 light years wide (and I'm just throwing this number out for the purpose of this example).   Is the actual matter inside the black hole itself smeared throughout say 9 light years, and anything sucked up in the future would be at 9.001 light years, 9.002 etc etc?

[onan]

Just watched the second episode. Nicely done, touching at moments.

[Agent : Orange]

No, it's definitely a good point.   Obviously not all black holes are still sucking stuff up.   So let me get this straight then - a  black hole is not really a single point in which mass/energy cannot escape (except with maybe Hawking radiation)?   Is that correct?   So if that's true, then the mass of the black hole is actually smeared around the cone, and the black hole actually has a real dimension?

Classically a black hole is a single point of infinite density - all of the mass of the black hole (which is a finite amount) is located at the center. But the problem with this picture, the picture that general relativity gives us, is that you can't make things arbitrarily small without quantum effects becoming important. It's thought those effects will smear the matter out over an area (related to the uncertainty principle). So our best picture - which is incomplete - says that the mass is located at a point. But no one thinks that's really the whole story. We don't know the exact details that quantum gravity requires but we have a vague notion of what we think it will be like and must rely on these (hand waving) arguments.

I always thought that the mass of a (non rotating) black hole was actually at the singularity, and the event horizon was just a "point of no escape" and not necessarily a "boundary of matter."   Meaning, let's say the event horizon of a very old non accreting SMBH is 10 light years wide (and I'm just throwing this number out for the purpose of this example).   Is the actual matter inside the black hole itself smeared throughout say 9 light years, and anything sucked up in the future would be at 9.001 light years, 9.002 etc etc?

You're quite right when you say the event horizon is a point of no escape and not a boundary of matter. All matter lives inside the black hole presumably near the center. But strange things start to happen at the event horizon of a Schwarzschild black hole. Observers far away from the black hole (ie not affected by it) will see light from stuff that's thrown in get more and more red, and time will appear to run slower and slower for that object. Eventually it's frozen image will just fade away, too redshifted to see. But to the guy falling in feet first carrying a beacon, nothing will seem to happen as he crosses the event horizon and will notice nothing out of the ordinary until the difference in gravity between his feet and head increases so much that he's torn to ribbons. In fact, inside an event horizon the distinction between time and space can be thought of as flipping with respect to one another- so for anyone that crosses the horizon the singularity lies in your future instead of right ahead of you and escape is as impossible as traveling backward in time. 

The event horizon (the Schwarzschild radius) is itself a function of mass so as the mass inside the black hole grows so does the event horizon. This is an important reelationship that's used heavily in arguments about black hole entropy.

[Agent : Orange]

So I'm sure everyone heard about it by now but for completeness...

http://www.nature.com/news/b-mode-1.14884#/News

Cheers!!

[Agent : Orange]

http://youtu.be/ZlfIVEy_YOA

[area51drone]

Drudge is declaring Cosmos a "ratings disaster."   

[area51drone]

Just watched the second episode. Nicely done, touching at moments.

I just watched it, and the way it ended was terrible.   I believe in the first series, Sagan was describing the animation as it went along.   They should have included that audio with it.  Oh well.  Although I think some of the examples of evolution they did in this episode were easier to understand, I liked the Japanese crab from the first.  Regardless, I'm looking forward to the next one...

[area51drone]

So I'm sure everyone heard about it by now but for completeness...

http://www.nature.com/news/b-mode-1.14884#/News

Cheers!!

Maybe I'm just cynical, maybe I need to go back and re-read your posts, but really, what difference does this make?   Wasn't it already pretty much accepted by the scientific community?   It may show that there was inflation, but it still does not explain why the big bang happened in the first place.   THAT would be news.

In other news, Hekaran scientists presented preliminary research of gravity pulse waves created by gray alien warp drives coming from the gamma quadrant.  It turns out that these gravity waves were mis-interpreted by Earth scientists as simple big bang inflation.

[onan]

I just watched it, and the way it ended was terrible.   I believe in the first series, Sagan was describing the animation as it went along.   They should have included that audio with it.  Oh well.  Although I think some of the examples of evolution they did in this episode were easier to understand, I liked the Japanese crab from the first.  Regardless, I'm looking forward to the next one...

I liked the aspect of spirituality and thought the ending was meant to give a sense of awe. It worked for me.

[area51drone]

I liked the aspect of spirituality and thought the ending was meant to give a sense of awe. It worked for me.

I suppose.  Maybe it was the final sagan audio clip that bothered me, it was clear that clip was meant to lead to something, and then the show just abruptly ended, and the clip seemed seriously out of context.   I'm just being picky.

[zeebo]

..In other news, Hekaran scientists presented preliminary research of gravity pulse waves created by gray alien warp drives coming from the gamma quadrant.  It turns out that these gravity waves were mis-interpreted by Earth scientists as simple big bang inflation.

Yeah but they're still gonna snag a Nobel Prize out of it, if for different reasons.