MAP Satellite Launch

PineGreen writes: "Tomorrow, MAP Satellite is to be launched. MAP is the first space mission to measure Cosmic Microwave Background (CMB) fluctuations after the famous COBE who was first to detect fluctuations in the CMB. It is supposed to do the job with an unprecedented accuracy. There were several successful balloon experiments (Boomerang, Maxima) and interferometer experiments (VSA, DASI, CBI), some of which still haven't published their data. But of course, we are all waiting for the big European Planck mission in 2007. Measuring CMB fluctuations can tell us a lot about the universe in which we live, its constituents and its geometrical properties."

Comments

abbreviations

[jfinke]

I wonder if it is possible to use any more abbreviations in that story....

L2

[Manhigh]

Forgot to mention this is the first mission to orbit Earth-Sun Lagrange Point 2, soon to be followed by Next Gen Space Telescope.

Re:Big Bang or just a fizzle?

[Anonymous Coward]

I wonder, does the existence of background radiation prove the idea of the Big Bang?

Nothing can prove a theory correct. However, the existence of the CMBR is considered some of the strongest evidence in favor of Big Bang models.

My doubt mainly stems from the fact that the Big Bang is essentially a relativistic theory whilst it makes claims on objects with small diameters. (Also my objection to black holes.)

Do you think that relativity doesn't apply on small scales? The theory of quantum electrodynamics (verified to one part in 10 billion) would beg to differ. Of course, that's special relativity, not general, but general relativity isn't expected to break down until near the Planck scale (10^-34 meters). Thus, the discrepancy only becomes important near singularities -- i.e., the Big Bang and centers of black holes.

As for black holes, general relativity is applicable at horizon-size scales, so there should be an event horizon (and thus black holes should exist), but we don't really know what goes on at the very center of a black hole. As for the Big Bang singularity, we don't know what goes on there either -- but Big Bang cosmology doesn't require there to be an actual singularity, just that the universe was once very small, dense, and hot.

Probably someone in the crowd is a bit more clued in than I am and can point me to an interesting article that say, proves the existence of Black Holes

Like I said, nothing can prove a theory correct. If you're looking for evidence in favor of black holes, there are all sorts -- ranging from the detection of extremely massive, compact, dark objects, to huge energy jets that are so strong that they can only be powered by gravity, not fusion or anything, to stuff falling onto these dark compact objects that dim out of sight instead of producing the huge explosion we'd expect if they rammed into the surface of a neutron star at relativistic speeds, to the destabilization of orbiting matter at the location just outside the horizon where general relativity predicts no stable orbits can exist, and so on.

- that, for all intents and purposes, will resolve my objection that a relativistic model cannot answer what is fundamentally in the realm of quantum theory.

I don't think you understand what you're objecting to. Simple dimensional analysis tells you that quantum mechanics isn't important on scales of a few kilometers (the size of the smallest stellar black holes), any more than quantum mechanics is important when you're driving to work. It's a regime in which classical physics is highly applicable. Thus, it doesn't affect the formation of event horizons and things. It may affect the formation of a singularity in the center, but that's only well after an event horizon forms. And if an event horizon forms, it's by definition a black hole, regardless of whether there's a singularity in the middle. (Of course, quantum mechanics is important for Hawking radiation, but you get Hawking radiation even when quantum mechanics isn't affecting the gravitational physics very much -- just when the gravitational physics is affecting the small vacuum fluctuations. This is the "semiclassical approximation" where you can ignore the backreaction of quantum matter onto spacetime geometry because its effects are so small.)

An alternative to the Big Bang, to explain the radiation could be that simply the enormous pressure at some point set off these waves.

"At some point"? We receive the CMBR extremely uniformly from every direction in the sky. Why would there be this "enormous pressure" at some particular point in space? (Note that the Big Bang was not "an explosion" at some specific point in space, but rather the expansion of all of space from a point.) And why would "some enormous pressure at a point" generate perfect blackbody radiation? Apart from the background radiation, how do you explain the fact that the universe is expanding, and has been for as far back as we can see? What do you extrapolate from that about the early size of the universe? How do you explain the fact that the background radiation was once much hotter, in every direction we can see? How do you account for the observered ratios of light-element nuclesynthesis? Etc. etc.

Perhaps the universe expands and contracts in a sinusoidal manner, but never actually becomes a singularity.

That's possible, in a sense. Classically, there's no way for that to happen -- you have to "fine tune" the conditions to a ludicrously precise degree in order to get a bounce; the Penrose/Hawking singularity theorems show that under realistic generic conditions, it will never happen -- you'll get a classical curvature singularity. (And even if you do get a bounce, the bounces don't last for very long.) On the other hand, it is possible that if the universe crunches down to the Planck scale, then quantum gravity effects will take over and produce a "bounce". However, that doesn't rule out Big Bang models, because as I said above, all that cosmologists actually assume about those models is that the universe was once small, dense, and hot.

The idea that there actually was an initial singularity is something that a lot of cosmologists doubt, but the media seems to equate that with "Big Bang cosmology". In reality, the existence of a singularity is what general relativity predicts, but nobody expects general relativity to apply at the Planck scale due to, as you say, quantum effects.

Re:Big Bang or just a fizzle?

[jafuser]

Ok, I am not an astrophysicist, but I did just get the highest score in my astronomy class (by a margin of 10% even) :)

The general temperature of the cosmic background radiation is evidence of the big bang. I think it was something close to 2.7 degrees Kelvin. This temperature is a minimal black body temperature which exists everywhere in the universe, no matter which direction we look. Apparently the uniformity of this tells us that as the universe is expanding, that the temperature will go down. So someone looked at this and figured out that if you play the expansion in reverse, that as the universe was smaller, this background temperature would have to be higher, eventually focusing on the big bang.

When we use very sensitive equipment and draw an image from measurements of this black body radiation, we at first can see an effect caused by doppler shift becuase our planet is moving through space. Space seems hotter in the direction we are going, and cooler in the direction we are coming from.

Finally, if we adjust for this doppler effect, and look at the temperature at even much higher accuracies (something like millionths of degrees) we start to see a nonuniform image of random warmer and cooler spots across space.

One major significance of this is that if we measure the average distance between the cooler and warmer spots, we can compare this to a mathematical model which will tell us the curvature of space itself (on a very large scale) . If they match a mathematical model of flat space, then space is probably flat. If the patterns are larger or smaller than the flat model then space is probably curved, either hyberbollically or spherically.

Of course, a non-flat space has some interesting consequences. The angles of a triangle don't add up to 180 degrees, and parallel lines will not stay equidistant (they may merge or converge) as they due in euclidian geometry.

This satellite will provide a higher resolution image than COBE.

I just woke up so I probably left out something important or really said something stupid...

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Some References

[Old-Claimjumper]

I realize that I am breaking some rule or other by posting actual information, but here are two good book for the non-PhD Cosmologist to get an introduction to the current topic.

The First Three Minutes, Steven Weinberg, Basic Books, 1977
ISBN : 0-465-02435-1

This is one of the first books to explore the physics behind the 2.73 degree Background Radiation in a way that mere mortals could understand. The Physics at the time couldn't explain before a few milliseconds into the big bang, but Weinberg did a good job of explaining what we knew and how we knew it from the first few milliseconds up to the first three (and a half...) minutes. Steven Weinberg went on to win a Nobel Prize and also explain how Electromagnitism and the Weak force are actually the same early on in the game.

At the other end of the spectrum is a brand new book that takes the unique approach of focusing on the concepts of Zero and Nothing and showing just how much follows. It ends up giving a good up-to-date view of the same physics as The First Three Minutes, but from a current viewpoint. I think that just a wee bit more Math describing the inflationary phases of the early universe and the idea of quantum pair production would have been appropriate, but for the most part the book is a good non-astrophysicist intro to the background radiation and the start of the universe as we know it twenty-some years after Weinberg's book.

The Book Of Nothing, John D. Barrow, Pantheon, 2000
ISBN : 0-375-42099-I

Note, this would be a good book for a /. book reviews.

In Other News....HESSI Delayed Again

[Renstar]

In a somewhat related story, NASA's HESSI (High Energy Solar SpectroScopic Imager) spacecraft has had its launch delayed again. It was supposed to launch July 4th 2000 but had to have many of its insturments recailbarated at GSFC when JPL shattered the mounting brackets by mistake in a vibration test. After that, a problem in the Pegasus launch vehicle was discovered and had to be fixed, delaying launch until 3 weeks after the X43 failure. KSC and Orbital Sciences (makers of the Pegasus) cleared HESSI for launch. NASA decided to wait until the X43 investigation was over. This caused HESSI's launch to be delayed indeffinatly while at leist 6 spacecraft launch this summer (NASA refuses to work them back in). This is a problem. HESSI is designed to study the solar maximum, which has practically been missed, and it will fail its mission parameters if not launched by September 2001. This is NASA's fault, not the HESSI team. The HESSI team has done everything possible to get this bird in space, it just hasn't happened. Pull and hope that this bird flies (After the JPL accident, I worked on calibrating the Roll Angle Sensor (RAS) for the star-tracker navigation telescope on board).