Dark Energy is Real

first_mos.jpgThis is apparently the post I wasn’t supposed to publish. I wrote it yesterday, and had it somehow utterly disappear from my HD after a crash. I then was writing it in wordpress and had Firefox crash on it before the first auto save…

In a really cool press release that I got yesterday but couldn’t share (silly embargoes), it was announced that observations of distant galaxies support the idea that Dark Energy is most likely a real force or field that we don’t yet understand (as opposed to it being a side effect of us not understanding gravity – it looks like we really do understand gravity). (image left of galaxy spectra from VIRMOS)

Now, at first look, this doesn’t sound that specific our exciting. In fact, the vagueness of our understanding of Dark Energy (and Dark Matter, but this isn’t a post about Dark Matter), lead many people to randomly announce (often in email) that they “don’t believe in Dark Energy.” I even had one of my colleagues last week tell me that he doesn’t believe in Dark Energy (or Dark Matter, which I’m still not talking about). If astronomers can’t convince random physicists (who will admit they haven’t read any of the findings in the past couple years) that Dark Energy is real, how can we convince the general population.

Admittedly, dark energy is something that we can’t see, can’t taste, can’t touch, can’t measure directly, and can’t even precisely mathematically describe. This makes it somewhat hard to sell as real (although it doesn’t appear to have been to hard a sell for the boogie monster, tooth fairy, and snow yeti). So, this raises the question, how can we know Dark Energy exists?

Well, just like the invisible men and invisible women of fiction are detectable through their footprints (a push on the ground), are detectable from the lamps and other furniture they throw at more visible heroes and villains (pulls on objects), and are detectable through the punches they throw (a very definite push), dark energy is also detectable through the push it exerts on the universe.

Dark energy was first detected in 1998 by supernovae observing teams who were working to measure how the expansion rate of the universe has changed over the 13.7 billion years the universe has been around. They expected that the gravitational mass of everything in the universe on everything else would cause a breaking of the expansion. What they found instead was that some mysterious force / field / extra term on gravity / etc is pushing the universe apart and accelerating the expansion. Since this weirdness didn’t have a name, and the name dark energy wasn’t already in use, the weirdness was named Dark Energy.

Since that fateful discovery, people have been working to figure out if dark energy has always been around, if its push has always been the same. Using supernovae, astronomers were able to figure out that dark energy has been around at least as far back as they can go with supernovae. What they haven’t been able to figure out is if it was something related to us not understanding gravity (a constant, back of the mind concern), or if it real is some sort of field effect that just sort of permeates all of space.

And not knowing makes good astronomers apply for telescope time so these questions can be answered.

In a paper published in Nature today, 51 astronomers led by Luigi Guzzo announced that studies looking at a large selection of galaxies in clusters at high and low redshifts (from the VIMOS VLT Deep Survey and the archived 2dF Galaxy Redshift Survey) have found that the motions of galaxies in clusters at high redshifts indicate that 1) we understand gravity, and 2) dark energy has nothing to do with gravity.

Unfortunately, the press release was a little vague, and perhaps even a little contradictory, and I don’t have a subscription to Nature. Here is what it says:

Within current uncertainties, the measurement of this effect provides an independent indication of the need for an unknown extra energy ingredient in the ‘cosmic soup’, supporting the simplest form of dark energy, the so-called cosmological constant, introduced originally by Albert Einstein. The large uncertainties do not yet exclude the other scenarios, though.

“We have also shown that by extending our measurements over volumes about ten times larger than the VVDS, this technique should be able to tell us whether cosmic acceleration originates from a dark energy component of exotic origin or requires a modification of the laws of gravity,” said Guzzo.

I read this to say, they see evidence of dark energy at high redshifts, it isn’t possible to discard dark energy as not existing, it looks like dark energy isn’t a problem with gravity, but there are error bars, and Guzzo thinks continued analysis will make the error bars tiny enough to end this debate.

It’s a start. And it means dark energy is real.

So stop sending me email 😀

15 Comments

  1. Doc Kinne January 31, 2008 at 10:52 am #

    Sorry, Pamela, I’m going to send you this “email.” 🙂

    At the risk of making you embarrassed that you ever were one of my teachers – and this is a dead serious question on my part – how does this result (or any other recent result) invalidate other theories, specifically MOND?

    Now I’m coming at this simplistically, I know, which is why I value your opinion. I KNOW there is an effect out there that is not explainable by our current mathematics. I’ve seen the galaxy rotational data and understand it enough to know this (in terms of Dark Matter…which this post is not about). But I get weirded out when we’re told to accept something that we can taste, touch, feel, detect, or measure. You say we know that Dark Energy exists because we can see its effects, and I agree we do see something being effected, but I don’t put it in the same bucket as that of a Black Hole, somehow.

    Black Holes are “easy” to detect once you know what you’re looking for. Gravitational lensing and videos of the rotational speeds of stars in the Galactic Core are damn convincing. SOMETHING has this amount of mass in this amount of volume. It COULD BE all the universe’s missing socks, yes, but if its in that small of a volume, I’ll agree to call it a Black Hole.

    Dark Energy and Dark Matter (sorry, I’m slightly more familiar with Dark Matter) is something different in my mind. Isn’t it possible that what we are seeing is the effect, for some reason, that due to distance, etc. our mathematical understanding just isn’t quite working out? I am NOT saying that Einstein is wrong, you know me better than that. But just as we discovered that Newton needed a “bit of tweaking,” via Relativity, to work at great speeds, might we be seeing something that needs a bit of tweaking to work at great distances with such large amounts of matter and scale?

    Along these lines I’ve always liked the MOND theory. I get the impression that you don’t. Why?

    Because your “Why” makes a difference. 🙂

  2. Richard B. Drumm January 31, 2008 at 11:41 am #

    One of these days I’m going to make up a t-shirt that says:
    Dark Energy is REPULSIVE!

    I crack me up! 😀
    On the dark matter front, I make sure to mention Vera Rubin when I talk to Girl Scouts and tell them that some of the -BEST- astronomers are women. It never fails to make ’em smile!
    Rich

  3. Jorge Schrauwen January 31, 2008 at 1:10 pm #

    To get Dark Energy accept change it name to some cool covert sounding name. Then create a conspericy around it that some other cool named organizations wants us to think its fake but the smart scientist can’t be fooled… and the public will be sold.

    ps: my statists exam was a disaster!

  4. Freiddie January 31, 2008 at 11:16 pm #

    I wonder if dark energy and dark matter exist. (I’m uncertain)

  5. rexray February 1, 2008 at 10:15 pm #

    Is it possible that we’re seeing the effects of gravity from matter somewhere at the edge of the universe? Using the universe-is-a-balloon analogy, it seems that the “skin” of the balloon has more matter than the contents of the balloon. If you were in the center of the balloon, you might feel a gravitational pull coming from all directions around you. Therefore, matter from the big bang could still be densest at the ever-expanding edge of space and have a spherical pull on everything within… which might seem like repulsion if you’re right there in the middle of it all like we are.

    Or am I just totally in the “dark”?? 🙂

  6. Freiddie February 1, 2008 at 10:22 pm #

    To rexray,
    The balloon analogy uses only and ONLY the “skin” of the balloon. Whatever that is inside or outside the balloon is not “space” at all. The analogy is a reduced dimension analogy – i.e. our space is 3D (or 4D or more) and the analogy of the balloon is its 2D surface and only that. We can and only live on the surface of the balloon, not “inside” the balloon, which isn’t space at all. There is no “center” in this analogy because every point on the surface of the balloon is on equal footing with any other point on the surface. Remember, the analogy only draws comparison only on the surface. Got that?

  7. rexray February 1, 2008 at 10:42 pm #

    To Freeddie,

    But let’s say this is a different balloon analogy… Maybe we can use the more pleasant “crusty cake” analogy: The universe starts off as a microscopic (or not) point of “all matter” and suddenly expands creating our 3+ dimensions inside of itself. As it expands, the bulk of the matter is around the surface/crust of this spherical(+/-) cake and some of it perpetually pulls away toward the center a little at a time creating galaxies and non-luminous substances to fill the void (i.e. “cake”). After all, we believe the universe is still expanding (and hasn’t reached it’s maximum expansion yet), so is it too far fetched to hypothesize that the bulk of matter is beyond the reach of our telescopes, but is still having a gravitational effect none the less? Granted this is assuming the the universe is finite and that there is only just so-much matter in it. But there could still be other universes beyond ours which also experience the same cyclic boom behavior. So, there may still be an infinite aspect to it all.

    Since we’re having a hard time explaining the repulsion effect (anti-gravity? I think not), it might be more easily explained by the gravity of the still-expanding-away-from-us shell of matter form the formation of our universe. At the risk of sounding even more ignorant, I’ll stop now. 🙂

  8. Freiddie February 2, 2008 at 1:10 pm #

    Note: Please don’t take this as an criticism, I’m only trying to point out this that doesn’t feel right in your model.

    The crust cake analogy is something that is asymmetric. You are also assuming that there exists a border to the universe. Of course, I don’t know if this is true (and how do scientists think of it), but I find this less than ideal. For the time being, the universe is more likely to expand forever, due to the acceleration in expansion (one of Pamela’s posts has it).

    Also, a shell of matter have no influence in terms of gravity on anything inside it. If you do the calculations right, any spherical shell has no gravitational influence on the interior matter because gravity on opposite sides cancel out.

    It’s also hard to imagine cyclic universes. During a universe’s lifetime, entropy increases, and I don’t know of any mechanism that can decrease it and hence set the ground for the next universe (other than by an implausible chance).

    But I do find the dark energy to be a little disturbing. I don’t see why we should have a “aether”-like field permeating everywhere, or have a cosmological constant that was later discarded and then re-added in a new form. It feels a little awkward. It also reminds me of a field called inflaton and Higgs field, for some reason…

  9. Brian Hunt February 6, 2008 at 11:39 pm #

    Have you read or encountered this hypothesis?

    http://www.dailygalaxy.com/my_weblog/2008/01/scientist-says.html

    “Professor Jose Senovilla, and his colleagues at the University of the Basque Country in Bilbao, Spain, have proposed a mind-bending alternative. They propose that there is no such thing as dark energy at all, and we’re looking at things backwards. Senovilla proposes that we have been fooled into thinking the expansion of the universe is accelerating, when in reality, time itself is slowing down.”

  10. Greg Marlow March 1, 2008 at 8:11 am #

    Could a weakening gravitational force with time explain the observations attributed to dark energy? If matter contains an energy component with a wavelength equal to the size of the universe, it would explain why gravity started out stronger in the beginning and got weaker with time. If you do the math for 14 BLY, you will also see that this wavelength’s energy compared to the rest energy of an electron is on the order of gravity’s strength compared to the strength of the electric force.

  11. SteveV June 27, 2008 at 5:41 pm #

    I believe dark matter & dark energy exist.

    I think they may be poorly named however… and ‘dark matter’ may not end up being matter at all.

    Perhaps we’ll end up seeing it as a side-effect of gravity.
    E.g. String theory describes our universe made up a fabric of strings. Gravity displaces space-time, creating a gradient attracting matter together. Perhaps this gradient of dense space-time exhibits a friction upon the adjacent fabric of space.

    Think of it like this…
    You put a golf ball inside of a spongy material. The squeezed spongy material around the golf ball has a tension energy of it’s own.

    http://stevevinsac.blogspot.com/2008/06/star-stryder-blog-archive-dark-energy.html

  12. SteveV June 27, 2008 at 5:47 pm #

    I read a couple of earlier posts about the balloon & crusty-cake analogies & just wanted to point something out…

    The universe isn’t finite, it’s infinite. The ‘Big Bang’ is often misconstrued as being a finite singluarity.

    New theories are gaining support that there may not have been a singularity, but a ‘brane-collision’ that created an infinite universe.

    http://stevevinsac.blogspot.com/2007/10/big-bang-is-big-baloney.html

  13. Paul Tatham July 24, 2008 at 5:23 am #

    I believe Dark Energy is much simpler than scientists think.
    There is no mysterious force, simply the effect of gravity.
    All galaxies have a fixed momentum given to them soon after the Big Bang. Momentum is mass x velocity.
    So if velocity increases, mass must decrease. And how is that possible?
    The answer is in understanding what ‘space’ is and what ‘gravity’ is.
    Bluntly – Gravity is the back emf from positive electromagnetic waves, mostly light waves. It acts only on negative particles = electrons, and that is fundamental.
    Space is electromagnetic waves produced by charged particles. The waves / fields are necessary for the particle to move.
    The time to produce a field when energy is added to a particle is inertia – this is mass.
    So as a galaxy moves away from gravity, the spiralling orbits of electrons change, so requiring less field = less mass (the field is mass because the field is the result of inertia – a particle has no mass. Yes, a particle has no mass).
    Less mass means higher velocity under constant momentum.
    Read more free by going to http://www.lulu.com and downloading ‘The Subtle Source of Dark Energy’

  14. Dale B. Ritter, B.A. January 18, 2009 at 12:25 am #

    Thanks for the incisive coverage of recent cosmology, with discussion of dark energy. The depths of space are mostly a spaceon, an ocean of spacons. One way to model that is by differential system analysis using quantum and relativistic wavefunctions to define energy particles tologically, and applying the solved relations to image the force fields: time, probability, magnetic, gravity.
    This model is named CRQT: Clough Relative Quantum Topodynamics. It generates a deepspace built up from a spectrum of spacons with regular, trace level fields of time, probability, magnetism, and gravity. The spacons exist in a loose matrix of force nodes, bonded by gravity and probability exchanging quanta in extensive, aligned pulsative arrays.
    RQ space and more grand unified topics are on view online as the book titled The Crystalon Door at: http://www.symmecon.com .

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