Thought of the Week: Dark Universe

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Silesian Planetaruim (not the one we went to).

Silesian Planetaruim (not the one we went to).

I was at a planetarium this weekend with Little Satis and my family, and we watched a wonderful short presentation on dark matter narrated by the smooth-voiced Neil deGrasse Tyson. (Mrs. Satis actually dozed off because of his voice.) I’m pretty partial to anything space related, and although I didn’t learn any astounding, never-knew-that-before statistics, it re-awoke the old fascination in me about the origins of the universe, and space in general.

One of the revelations of the presentation was the fact that all of the matter and energy (stars, planets, heat, light, etc.) that we can observe represents about 5% of the total contents of the universe, calculable by the gravitational effects of dark matter on the rotation of galaxies and the expansion effects of dark energy on the universe as a whole. But things like that make me wonder, because there are a number of far-flung theories out there regarding the nature of the universe as a whole, and as an absolute lay-person I sometimes feel like I can almost piece it all together, if only I was a little brighter.

 

This would mean that every black hole in our universe is in fact a lower-dimension universe in and of itself…

 

Dak matter strings.

Dak matter strings.

String theory (to my limited understanding) essentially postulates that all particles in the known universe are actually space-time representations of ‘strings’ that permeate the entire universe. What this essentially means is that this hydrogen atom that I see spinning away from me is actually part of an infinite string, pulled along by the expansion of the universe itself. If such is the case, then it makes me wonder whether ‘dark energy’ is required to explain the expansion of the universe. After all, energy is required to explain the kinetic movement of objects in a three-dimensional space. However, if the movement of objects on the largest of scales is actually the act of the universe dragging them along, no energy, as I see it, is required.

It does still raise the question of why the universe is expanding at all, but what if that expansion is purely relative? For example, it’s been calculated that as the universe expands, it cools. Therefore, it was hotter in the past than in the present. But if our existence in the universe is dependent on the relative conditions at the moment in time in which we exist, then isn’t it just as likely that earlier in the universe’s life, the relative heat was no greater than it is now? In other words, to an observer ten billion years ago, the universe was no hotter than it is now, although for that observer, the universe was still hotter in the past and cooler in the future.

Does that make any sense? If it does, it means there may be no such thing as ‘dark energy’ at all, since the movement of distant galaxies and the temperature of the universe as a whole is entirely relative to the observer.

Super neat image of a black hole (not real).

Super neat image of a black hole (not real).

Another theory that I quite like the idea of is that the entire universe is actually the interior of a higher-dimension black hole. This is fun, because it explains the big bang as the point of creation of that singularity, and the expansion of the universe as the continued accumulation of matter and energy from that black hole’s event horizon. It could even explain the increasing rate of the universe’s expansion by the black hole going through a period of increased accretion, perhaps because it’s moving through a space of higher-density matter/energy in that higher-dimension universe.

This would also mean that every black hole in our universe is in fact a lower-dimensional universe in and of itself, which is an exciting thought. It aligns the thought that one can’t ask the question “what is outside the universe” because the universe is the entirety of existence with the thought that nothing can escape a black hole once in it in the first place. It makes me wonder what forms of life might exist inside black holes that we would never know of…

So that only leaves dark matter, which…well, I don’t have time or inclination to attack that now. This essay will have to stand as-is for the moment. Still – it’s exciting stuff. What do you think of the origins of the universe and the fate of its continued expansion?

Featured image adapated from http://kipac.stanford.edu/kipac/media.

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Thought of the Week: Measuring the Lead (Cosmos Question)

Cosmos_spacetime_odyssey_titlecardLittle Satis, Mrs. Satis and I have quite come to enjoy watching Cosmos on Sunday evenings. Despite its often over-sensationalized tone, the show covers some intriguing topics and presents them in a famously easy-to-understand way. However, as with all simplification, sometimes crucial details are missed or skimped, leaving me at least with a deeper yearning for understanding.

Which is hopefully the point of the show.

Last night’s episode told the tale of Clair Cameron Patterson, who pioneered a now-common method of dating rocks to determine the age of the earth. To be fair, it wasn’t his idea but that of his principal investigator, Harrison Brown; yet Brown allowed Patterson to do the work as a PhD student, and kept him on even when uprooting and moving his lab to California, and when Patterson’s experiments seemed to be failing miserably.

The essence of the episode was in fact to showcase how Patterson inadvertently revealed the extent of lead toxicity in the environment around us, and fought for decades afterward to remove lead from paints, petrols and pipes. Because of this, the hardcore science of the experiments was, if not scaled back, not dived into. And it left me with a burning question, which I’ll get to in a moment.

 

How on earth could this method of comparison work?

 

You see, to date the earth (or any piece of rock for that matter), one of the primary methods is to measure the amount of uranium in the sample, and compare it to the amount of lead. Why does this help? Because uranium is an unstable radioactive element, which decays into lead over a very long period of time (the half-life of 238U being almost 4.5 billion years). Because this decay occurs at a constant rate, by comparing the amount of uranium to the amount of lead the age of the rock can be calculated.

The Holsinger Meteorite, part of what blasted a half mile-wide crater in Arizona.

The Holsinger Meteorite, part of what blasted a half mile-wide crater in Arizona.

From this point, the episode covered the discovery that Patterson’s initial measurements were skewed because of the fact that lead was present in the atmosphere and soil in unnatural quantities, and veered off into the politics of fighting the oil companies who were putting lead in fuel as an “anti-knock” agent. But it left me wondering: how on earth could this method of comparison work?

After all, we can measure the amount of uranium and the amount of lead in a rock as it stands today, but how can we possibly know what proportions existed in that rock three or four billion years ago? After all, lead is as naturally-occuring an element as uranium, so presumably there was lead in primeval igneous rocks as well as uranium. If this was the case, how to tell the difference?

So I had to do a little research, and the answer, as far as I can tell, is this: the key was using zircon crystals. Zircon, it seems, actually rejects lead from its crystalline structure: in other words, zirconium and lead don’t mix. This was presumably known at the time, which meant that the traces of lead that were found in zircon crystals could only be from uranium decay. This implies that when the rock was first formed, there was no lead in it at all. Since the rate of uranium decay is known, then the amount of lead can be directly used to backward-calculate how long it took to form, ergo the age of the rock.

Zirconium crystals, complete with uranium and lead.

Zirconium crystals, complete with uranium and lead.

Now what Patterson did was a little more complex, by comparing different isotopes of lead in a series of meteorite samples, but the principle is the same. The maths involved are a little beyond me at the moment (bringing back that rusty high-school physics!), but as I understand it, it nonetheless depends on the ratio of radiogenic (formed by radioactive decay) and non-radiogenic versions of lead.

What I still don’t understand about this, however, is that presumably meteorite fragments would have been decaying their uranium at the same rate as the earth, and how could we know in an iron meteorite fragment what amount of non-radiogenic lead would have been present 4.5 billion years ago?

Any geophysicists out there that could help me with this one?

Daily Photo: July 12, 2011

No idea what they were doing, but it looks pretty.

No idea what they were doing, but it looks pretty.

Part of a physics experiment at our local university. They were shining a laser at a copper spring, but quite what they expected to get from it I haven’t a clue. Very pretty, though.

Camera: Nikon D90          ISO: 1250          Focal Length: 105mm          Aperture: ƒ/5.6          Shutter Speed: 1/30

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