To say that the universe is massive is not an understatement
of science or sight. You have mass, your car has mass, and the Earth has mass,
yet this is nothing compared to the mass of other planets in our solar system
and especially our Sun. Looking through a telescope to see distant galaxies
that have around 100 billion stars each instills both a trifling feeling of
personal purpose and a unique awe reserved only for those realizations that
have moved man to myth and legend for millennia.
In science the universe has a measurable, knowable amount of
mass that can be calculated based on a number of theories, some of the most famous,
relativity for example, coming from Albert Einstein. The trouble though is that
the amount of stuff in the universe that can be seen only accounts for less
than 5% of all the mass in the universe. It is remarkable that this amount of
mass goes unseen, which is why it is called ‘dark’, but what is truly
astounding is that science does not know what it is. That is to say in our high-tech
‘knowledge is power’ world we cannot explain 95% of what is out there. Roughly
27% of this is called dark matter, a scientifically proven phenomenon that
gives galaxies their signature flat shape, and numerous other universal
characteristics, but has eluded cosmological attempts to be captured and
identified. Fascinating, still normal and dark matter only account for a
relatively small amount, what about the other 70% of the mass of the universe?
The question of dark energy is one of the most substantially
essential and basic unanswered question in the Universe. Because it deals with
the expansion of the universe dark energy not only speaks to where we have come
from, but also what the future may hold for our universe (though we certainly won't be around to see it). Its relatively recent
discovery enthralled scientist and has torn a rift between what we thought we
knew and what is actually happening.
From his Mount Wilson perch beyond the city lights of Los
Angeles in the 1920’s rockstar astronomer Edwin Hubble (namesake for the space
telescope) not only demonstrated that the night sky was made up of other
galaxies and not just stars from the Milky Way, but that the universe was
expanding. Just as the sound of an object deepens as the waves begin to
elongate when the object moves away, so too happens with the light of a distant
galaxy; except instead of becoming deeper as sound is perceived these elongated
waves appear red, the longer wavelength of visible light. That is why this observation was called red shift. Even
though we’re not in the center of the universe everything is red shifting away, which
makes sense if you think of a balloon that is being inflated. As
the balloon expands it grows out in its entirety in all directions from that
point of genesis, therefore giving any point the appearance that any other
point is moving away.
This view dominated the discipline for nearly seventy long
years until scientists began to ask some important questions based on the
nature of the mass of the universe with regards to this point of genesis, or
the so called big bang. If there is too much mass in the universe wouldn’t
galaxies start to attract each other and slow down like a cowboy lassoing a
calf, maybe even to the point where the expansion of the universe might reverse
as celestial bodies get hurled together because of their competing gravity?
Or if there wasn’t enough mass we could just expand forever at the same speed.
Turns out it wasn’t until 1998 when cosmologists realized that neither of these
were the case.
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| Tycho's Supernova Remnant In X-Ray |
The breakthrough came when studying type 1a supernovae.
Great distances are difficult to measure in the universe due to the
inconsistencies of light emissions; however these supernovae were known to give
off a very specific measurable amount of light. Using these exploded stars as a
ruler cosmologist could figure out how far away they were and the extent of
their red shift. These galaxies and stars were much more distant than anything
that had been surveyed before and scientists discovered that they were about
25% fainter than what they should have been, based on previous models. Because
the light that was observed was from farther away that meant that it was also
from farther back in time (a couple billion years or so), in the sense that
longer distances that light has traveled necessarily represents an older period
of the universe. These observations led scientists to assert that the best explanation
fitting the evidence was that the universe wasn’t just expanding, but actually
speeding up. This research was being done concurrently and independently by two
different teams, the success of which was revered by the Nobel Prize.
The amount of matter needed to accelerate the universe, and
space itself, gives scientists the 68% number, yet we still don’t know what it
is. There are about three main theories that attempt to shed some light on the
perplexing inconsistencies that give rise to dark energy. It could be a
property of space to the extent that the vacuum of space either has its own
energy density or a sort of quantum foam where particles spontaneously come in
and out of existence, in a similar fashion to how foam in a beer will form then
pop at will. Dark energy could also be some kind of new field or fluid, not
unlike the recent discovery of the Higgs Boson at CERN, but it is so small and weak
that our instruments cannot detect it. Or finally that Einstein’s theory of
relativity, and the basis for nearly all of what we think we know, is simply
wrong and another theory is needed.
The consequence of the questions surrounding dark energy
should not be lost on us. Whatever it turns out to be the answer will
fundamentally shift some of the most basic tenants of our universe. It will
impact the fundamental way in which science is conducted and how we go about
situating our knowledge in truth. Questions like where the universe came from,
what forces have given it shape, what is the nature of the interaction of the celestial
bodies, and what does this imply for the future of our known universe all
depend on a greater understanding of dark energy. And that is why dark energy
is the single most important question in our universe.
Deeper: The Dark Energy Survey is a scientific conglomerate that is currently using a highly sophisticated digital camera fixed to a Chilean telescope to peer back deep into the past of our universe to seek answers for dark energy. NASA has a great article about the dark side of the universe and one of the members of the original teams to discover dark energy, Alex Filippenko of UC Berkeley, gives a great, if not sometimes confusing, talk about the acceleration of the universe. Those curious about astronomy, including myself and my five year old nephew, can explore NASA's enduring educational contribution in the Astronomy Picture of the Day
