Thursday, August 26, 2010

12) Dark Matter: Mass/Energy Equivalence

We should remember that in every scenario where a substance or object succumbs to stress in a way that changes its nature (as discussed in the previous post), the principles of mass/energy equivalence remain in play, as do those of mass/energy conservation. For instance, the sun’s nuclear furnace works by compressing hydrogen atoms into helium (although, not quite so directly), resulting in a loss of mass in the form of energy. But, using the handy equation, E = mc2, we can account for the mass of the original hydrogen atoms even after this fusion takes place.

It is important to understand something else about mass/energy equivalence too, which is that it does not imply that mass and energy can be converted between states in some trivial way; it says that the mass of a body is a measure of its energy content. One way of thinking about this is to consider unit of measure conversions: one gallon of liquid is equal to 3.785 liters. Although this analogy is far from perfect (it doesn’t entirely hold up since mass and energy are not the same things), it does provide a decent insight into what mass/energy equivalence communicates. In a sense, they are two measures of the same quantity. Furthermore, within a closed system, mass and energy cannot be created or destroyed, only transformed.

Oddly, the principles of conservation of mass and energy are part of the supporting evidence for a Big Bang – they imply that everything that is now, must have always existed. The only thing we can assume then, is that all matter in the Universe must have existed within the singularity that preceded the Big Bang. Part of my intent here, of course, is to show that this is probably not true (and, given the current subject, I must point out that my use of the word probably is non-scientific).

So, where does this leave us? Throughout the many posts of this series on Dark Matter, we’ve talked about Gravity Wells, Gravity Bowls, the expanding Universe (Dark Energy), the rigidity of spacetime, E = mc2, and now, stresses and the conservation of mass/energy. What does it all add up to? To find out, we must add a final piece to the puzzle.

Monday, August 23, 2010

11) Dark Matter: Galaxy Formation and Spacetime Stress

In the previous post, I discussed some of the oddities revealed in the Hubble Ultra Deep Field Image. Specifically, the strange occurrence of what appear to be galaxies of vastly different ages occupying the same regions of space, within what is believed to be a snapshot of the early Universe itself (or, at least part of it). At the end of that post, I concluded that the most straightforward solution to this mystery lies in the likelihood that these galaxies formed in place (at their relative positions) as a result of something other than the Big Bang. The next question is, if the matter from which these galaxies were formed did not originate from the Big Bang, then where did it come from? And, what triggered their formation?

Let us think about the rigidity of space and Universal expansion again. As we discussed in a prior post, spacetime is incredibly rigid, but it expands nonetheless. And, despite this unrelenting and ever-accelerating expansion, the matter within it condenses into Galaxies rather than evaporating into space. Strange. Perhaps another analogy would be useful here.

Imagine taking a typical balloon filled with air, and then drawing several quarter-sized circles on it (the circles will be our galaxies).  If we then let the air out of the balloon, the circles will get smaller and move closer together until they become a cluster of small dots like Cheerios.

Now, what if we refill the balloon? As the balloon grows in size, the circles will expand away from one another in much the same way that galaxies in the observable Universe do. Interestingly, as this happens there will be no apparent central point away from which the circles move; instead, they will all simply drift away from one another.
Actually, the central point could be the center of the balloon, but this analogy is meant to be reflected by the balloon’s surface.
This analogy is quite good for conceptualizing Universal Expansion, except for one problem: as the balloon swells in size, the circles also enlarge. Conversely, galaxies do not grow as the Universe expands. Imagine blowing up this same balloon, but rather than the circles growing as the balloon gets larger, they move away from one another but remain the same size or even shrink.

Counter-intuitive, to say the least.

Since we have seen that familiar terms such as warping, stretching and bending can be applied to Spacetime (think Gravity Wells), we may wonder whether other physical attributes can also be applied, if only in metaphor. We know, for instance, that there are a couple ways to make water boil. One is to heat it up, but another is to subject it to near-zero pressure. If water is subjected to a near-perfect vacuum, it will begin to boil as the oxygen and hydrogen within it evaporate into gas. So, what appears to be a very stable substance under normal environmental conditions (at least in the typical kitchen), can be placed under more extreme conditions that cause it to break down in some way.

If you place the palms of your hands together so that they form a somewhat airtight seal and then cup them, you will experience the suction of air as the pressure between your palms drops below the pressure of the surrounding area. Of course, no matter how hard you try, you will be unable to produce a complete vacuum - or even a marginally strong one.

Yet, there are more extreme conditions under which cavitation occurs in more noticeable, and in some cases, damaging ways; such as on propellers and in pumps. Part of the trick to making submarines stealthy, for instance, lies in minimizing cavitation that can result when propeller blades slice through water at high speeds. Low pressure builds on the backside of the propellers, which produces noisy bubbles – a bad thing if you hope to remain undetected.

Could there be a counterpart to this in the realms of spacetime? Everything has boundaries at which it will succumb to stress and begin behaving outside of what we may think of as its typical character. Even a simple piece of steel will break if subjected to a greater force than it can withstand. Burning wood produces heat energy, but also destroys the wood. Compressing matter beyond a certain point results in fusion. In truth, the natural behavior of any substance is as much a function of environment as anything intrinsic.

So, in any case and for any substance, the characteristics of an object are changed by pressing it beyond certain limits - by changing its environment. Now, how would this apply to Universal expansion? What happens when something as incomprehensibly stiff as spacetime is eternally and relentlessly stretched? Can the fabric of space - spacetime itself - be stressed? And if so, what would happen?

Monday, August 2, 2010

10) Dark Matter: Odd Galactic Neighborhoods

If there isn't enough observable matter within a given galaxy to account for the fact that it does not simply fall apart, then what explanation (other than Dark Matter) is there for its formation? Is it possible that the galaxies formed in place, at their relative positions within the Universe, rather than being part of the debris field of some enormous explosion (the Big Bang)? It seems worth considering. Of course, if we do consider it, we must then ask where all the matter did come from.

Indeed we do.

For some, this question is enough in itself to dismiss any argument against the Big Bang altogether. Yet, I must hold out that to the open-minded, considering this question is no less sensible than believing that all the matter in the Universe originated from a singularity.

Speculation like this leads to many valid questions, not the least of which being, "What about all the other supporting evidence for the Big Bang?" A fair question to be sure, but that's what we're doing here; we're attempting to see if another hypothesis matches that evidence as well, or even better. Maybe there isn't one, but maybe there is. So, let us state the question a little more clearly: If there was no Big Bang, where did all the matter in the Universe come from?

Let us begin by considering the Hubble Ultra Deep Field Image, which shows thousands of distant galaxies glowing faintly against a deep-black backdrop. Oddly, the image seems rather unremarkable until you realize that these aren't just any galaxies - they are the most distant galaxies we have been able to photograph to date. In fact, if you haven't looked into it, click on the link above to learn more - it is well worth the time.

The actual distance to the galaxies in this image is not entirely straightforward. Yes, it took 13.2 billion years for the light we are now receiving from them to reach us, but the Universe has been expanding all along too. What's more, that expansion has, as far as we can tell, been accelerating the whole time as well. So, rather than attempt to establish an actual distance (which would add only marginal value to our discussion anyway), let's settle on the fact that they are ancient, and that we have yet to glimpse anything farther away. Perhaps even more importantly with respect to this discussion, is that this photograph is believed by many to show the galaxies as they were when the entire Universe was less than one billion years old (about 800 million years). I happen, not to agree, but won't expound upon the reasons until later.

In light of this, a couple things immediately leap out. First, as expected, this image appears to contain hundreds of young galaxies - that is, galaxies with shapes, colors and sizes to indicate that they were indeed captured during the early years of their formation. No surprise there. But, there are also what appear to be very mature galaxies, such as, HUDF-JD2 and others in the same region. This is odd indeed. Why would galaxies from largely the same region, and such an early period in the history of the Universe differ so greatly?

One possibility is that the more mature galaxies aren't as far away as they seem. We are not able to know for sure as yet, but astronomers believe they are. There is also the possibility that these galaxies just happened to have a larger starting mass than their neighbors, which could have accelerated their formation, in which case they are not older, but only further developed. This actually strikes me as quite plausible too.

But, what if they are older? How could galaxies from what appears to be the same region of space be of such vastly different ages? Are they drifters, just passing through the neighborhood? The evidence seems to suggest otherwise. Their redshifts, for instance, suggest that they are native to the regions where they appear.

The only explanation for this phenomenon having any degree of elegance is that they formed in place, but at different times. The only difficulty with this otherwise simple solution is the Big Bang. If all of these galaxies, old and new, are products of the same Big Bang event, then we have a disconnect - since we would naturally and quite reasonably expect all of them to be about the same age. On the other hand, if the galaxies formed place (at their relative positions) as a result of some other cause, then the mystery becomes....less mysterious - we need only discover what triggered their formation. And, fortunately, this may not be a difficult puzzle to solve at all.

9) Dark Matter: Distribution of Matter

In actuality, speculation about the origins of the Universe is very often speculation about the origins of matter. The Big Bang tracks everything back to a singularity – a single theoretical point where everything that is today, at one time existed in a condensed, ethereal state, which eventually exploded and evolved into the Universe as it is now. Given our observations and reflections on the Universe, this theory seems almost, but not quite reasonable.

First, the Big Bang is essentially targeted at two fundamental and hereto unexplained features of the Universe; 1) that it is expanding and 2) that there seems to be no other reasonable explanation of its origins. Beyond these two conditions, which the Big Bang seems particularly well suited to explain, are other observations that it doesn’t address quite so elegantly.

One of the biggest problems with the Big Bang is the distribution of matter. Deep space astronomy has revealed that there is a remarkably even distribution of galaxies in the Universe, which on first blush, seems to support the notion of a Big Bang. But this first impression quickly breaks down.

Although the galaxies are very evenly distributed, matter as a whole certainly is not. The fact that matter tends to coalesce into galaxies rather than more evenly cover the emptiness of space is inexplicable in terms of the Big Bang (discounting Dark Matter, of course). Given that there appears to be only about 30% of the required matter in a typical galaxy to account for the fact that it has formed at all (as opposed to simply melting into an indistinguishable haze of hydrogen), raises the question of why they exist. Why isn’t space simply filled with a huge cloud of hydrogen rather than well formed galaxies?

Most of us are acquainted with Albert Einstein’s famous equation, E = mc2, which expresses energy/mass equivalence (more specifically, that the mass of a body is a measure of its energy content). From the launching point of this known formula of nature, physicists have constructed many other theories that have unlocked far reaching areas of natural science, from helping explain the inner workings of the sun's nuclear furnace to constructing the nuclear bomb (some contend that this is not true, but I find it difficult to believe that the principles of conservation of mass and energy did not play a large role here). Indeed, this single equation has proven foundational to much of what we have come to understand about the Universe in which we live.

The underlying premise of this equation is that the Universe contains a fixed amount of matter - whether that matter happens to take the form of mass or energy at a given point in time is, in many respects, irrelevant. The implications of this are somewhat astounding, even to those of us who have long been familiar with them. Even the speed of light as the cosmic speed limit, which on surface appearances seems to be far removed from this equation, is inexorably linked – bound by the implication that the closer in velocity any mass comes to reaching the speed of light, the more of that mass is necessarily converted to energy. So, we are left with an unfortunate speed limit that seems disproportionately slow in comparison with the otherwise huge scale of the Universe.

Special Relativity asserts that matter is not created or destroyed (conversion of mass and energy), but only changes form between mass (relativistic mass) and energy (relativistic energy) . All of this matter, it is presumed, was present in a difficult-to-understand state within the singularity that preceded the Big Bang. And, although the equation, E = mc2 has been proven within the realms of matter (with some caveats), it makes no attempts at explaining where mass and energy first came from.