Is Dark Energy what we think it is?

Posted by Ethan on February 22, 2010
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Free energy will promulgate a forward leap in human progress akin to the discovery of fire. It will bring the dawn of an entirely new civilization — one based on freedom and abundance. -Sterling Allan

Of course, when Sterling Allan talks about free energy, he’s talking about natural energy from sources like wind and solar, not the violating-the-laws-of-thermodynamics type of energy.

There is, of course, no such thing as truly free energy, or energy that we can take out of nothing and use for something, which is why perpetual motion machines not only don’t work, but are physically impossible. (Although it is amusing to try to get as close as possible.)

But as many of you have noted about dark energy, there is a non-zero amount of energy that seems to be inherent to space itself. As the Universe expands, it appears to create more space, and hence, more energy.

Now, the energy density is tiny. So tiny that we didn’t even discover the existence of dark energy until 1998, and if you were to compare it to the energy stored in, say, the mass of a human body, you would have to spread a human being out over the entire inner solar system (to fill a sphere the size of the orbit of Mars) just to get the same density as dark energy, which is about two protons per cubic meter.

Now, while energy is ill-defined in general relativity, we understand energy and momentum well enough (as well as more complicated properties of metric spaces, which I will not go into) to know that dark energy should have the following properties based on our current observations:

  1. It should have a constant energy density everywhere in space.
  2. It should be impossible to add to or take away from that energy density.
  3. That energy density should also remain constant throughout time.

However, a recent paper has come out on the arXiv (and was discussed over on Cosmic Variance earlier today) that seeks to test that first assumption: is dark energy a constant everywhere in space?

Using a hypothetical improvement on a technique called atom interferometry (illustration above), they are proposing that changes in dark energy density could lead to changes in atomic motions, and could hypothetically exert a force on atoms.

Now, there are all sorts of reasons to believe that dark energy doesn’t exert a force on atoms. Namely, the following big ones:

  1. Dark energy, as far as we can tell, affects the expansion of space and nothing else, meaning it shouldn’t exert a force on atoms.
  2. You can only exert a force (whether you’re dark energy or not) if your field changes from point-to-point. On the other hand, dark energy is observed to be a constant everywhere in space.

But, it isn’t like we have a better proposal out there to try to perform some laboratory test on dark energy. Does it couple to matter? We don’t think so, but we haven’t tested it sufficiently to know for sure. Is it a constant everywhere in space? We think so, but we don’t know if it clumps (even a little) around masses like the Earth or the Sun.

There is so much we don’t understand about dark energy, and how the Universe’s expansion on the largest scales relates back to what we can observe in a laboratory on Earth that this is possibly the most exciting prospect to come out concerning dark energy all year!

So do I think this is likely to produce anything new? No, probably not. There are many good reasons to believe that we know what we’re talking about, but that doesn’t really matter. What matters is that — in order to know anything for sure — we need to do the experiment. This idea deserves to get a little bit of a buzz, if for no other reason than we need to throw ideas around about dark energy, and be open to the notion that what we’re seeing is so bizarre it could really turn our view of the Universe on its head.

But there still isn’t any truly free energy out there, not even if dark energy does change from point-to-point. Which is too bad… because if there was some, I could then move to phase 3. I’ll keep dreaming.

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Comments

  1. #1 Katharine
    February 23, 2010

    Regarding dark energy, I think people would understand it much better if you said ‘space-expanding awesome’ rather than ‘dark energy’, which implies it acts on matter.

  2. #2 John P
    February 23, 2010

    Dark energy reminds me of luminiferous aether. How long before the Michelson and Morley of dark energy appear on the stage?

    I’m glad you put a picture of a turtle in this post.

  3. #3 Douglas Watts
    February 23, 2010

    Like Katherine, I get thrown off by the term dark energy. Vacuum energy or the cosmological constant or “what makes Edwin Hubble a really cool dood” are less confusing, but that’s just me. The Casimir effect shows that vacuum energy can actually “do” something to real stuff on an observable scale, which is why I like it so much. I want a home science kit with the Casimir Effect included !!! And a cloud chamber.

  4. #4 Crux Australis
    February 23, 2010

    You said to exert a force, a field needs to change from point to point. Then how does a uniform electric or magnetic field exert a force on a charged particle?

  5. #5 Mu
    February 24, 2010

    Electric fields aren’t uniform, they still have a gradient depending e. .g on the distance of the particle to the plates generating it.

  6. #6 Bjoern
    February 24, 2010

    @Crux Australis: Ethan didn’t mean a “force field” like the electric or magnetic field, but a “potential field” (notice that he talks about energy!). As you perhaps know, both the electric and the magnetic fields can be expressed as derivatives of potentials. If the potential is constant, the electric and/or magnetic field will be zero, and there won’t be a force.

  7. #7 Ethan Siegel
    February 24, 2010

    Crux Australis,

    I am sorry for being so vague. You are correct: a uniform electric field and a uniform magnetic field are both perfectly capable of exerting forces on charged particles.

    But dark energy is “the other” kind of field: a scalar field, with a magnitude only, as opposed to electric and magnetic vector fields, with a magnitude and a direction.

    If you take the gradient of a scalar field, you get a vector field, which is necessary to exert a force. (Forces require a direction.)

    Glad we got to clarify (and thanks to Bjoern and Mu for the help)!

  8. #8 crd2
    February 25, 2010

    Ethan,

    You’ll be pleased to know that I have found dark matter, however it was only after I completed step 1 of your 3 step plan.
    :(

  9. #9 Katharine
    February 25, 2010

    I apologize if I missed the post, crd2 and Dr. Siegel, but was the plan

    1. Magically transport yourself to the edge of the universe and become an all-knowing being who can detect such things as ‘dark energy’ and ‘dark matter’
    2. ???
    3. PROFIT

    ?

  10. #10 Douglas Watts
    February 25, 2010

    So does dark energy as a non-directional, scalar field require an infinitely large Universe in which it operates? Or is the Universe so large, but not infinitely large, that the directionality is for all intents and purposes, undetectable? Or does Hubble red-shit expansion make it impossible for any two sufficiently distant parts of the Universe to be unable to communicate with each other, thereby destroying any possibility of directionality?

  11. #11 Douglas Watts
    February 25, 2010

    err … red shift ….

    my bad.

  12. #12 crd2
    February 28, 2010

    Even you have detected dark matter in your underpants at some point katharine. Dont play coy with me.

  13. #13 Thomas Neil Neubert
    March 1, 2010

    When you suggest that the hypothesized dark energy does not interact with atoms; I assume that you mean baryonic matter. But what about quarks, neutrinos and the other fermi-dirac particles of the stantard particle theory; and what about photons and gluons and the other bose-einstein particles of the standard model. And if none of those particles (and/or their fields) then does the hypothesized dark energy interact with supersymmetry particles (BE or FD)? Any thoughts; I just don’t know what is currently hypothesized?

    As well, I really do not have a clear idea what exactly the “dark energy” observations and correlations are? (e.g. are they redshift data or something else?) As well I don’t understand how dark energy is is somehow analogous to the Casamir effect?

  14. #14 Ron Horgan
    March 5, 2010

    Nathan, I was rather disappointed that the dark energy density is so low,2 protons per M3.
    I thought that quantum entanglement could be the separated particles interacting into and out of a dark energy field when separated by a distance eg some km apart.
    The analogy being an electric current in a conductor where an electron “in” is balanced by an electron “out” at the far end.The actual rate of individual electron flow in the conductor is slow MM per minute?
    This idea would require dark energy (or dark matter?)density to be relatively high.
    How do you estimate DE density? I guess on a galactic scale?
    If we were living in a dense soup of darkness, some of the more puzzling observations like identical twins knowing at a distance when the other is distressed might have a rational but dark explanation?

  15. #15 Ron Horgan
    March 5, 2010

    Nathan , sorry for the idiot question.
    I see the density of the large scale universe estimated from WMAP as 5.9 protons M3 with dark energy component 72% as about 4.2.
    I still like the dark dense soup as a possible medium for very odd events.
    Does your cafe have anything like this on the menu?
    Quantum entanglement is so cute!

  16. #16 Ron Horgan
    March 7, 2010

    Ethan, Sorry about getting your name wrong.
    I have some more innocent questions
    If the model of the vacuum energy of space is a sea of transient particles and antiparticles coming into “our “universe , and going back into into nothingness,
    might the notional protons of dark energy represent leakage and escape from this equilibrium.?
    Development of this idea might start to look like “steady state” with the source of the expansion being an inherent property of space rather than Fred Hoyles sartirical Big Bang?
    Coming back to the dense dark soup notion,might the vacuum energy of space represent a low proportion of the total dark matter which is present “through the looking glass”
    How much “material ” would be required to act as a “conduction medium” for quantum entanglement?
    A lot easier to ask than answer I expect!

  17. #17 Jon
    June 20, 2010

    I was trying to find out more about expansion and google calculated an equivalent in hertz.

    72 ((kilometers / second) / Mpc) = 2.33335907 × 10 to the minus 18 hertz.

    Does that mean the expansion sort of blinks or vibrates?

  18. #18 Clayne Directory
    June 28, 2010

    I can’t believe it’s Pluto’s 80th birthday. Having said this, the planet has yet to be visited by a spacecraft. We do know that the planet is mostly made up of ice which is one of the reasons it might be very difficult for any mission to take off.

  19. #19 Cellex-C Serum
    July 22, 2010

    The world’s largest steerable telescope – Robert C. Byrd Green Bank Telescope of the National Science Foundation – will provide scientists with valuable clues about the nature of the mysterious ‘dark energy’ believed to constitute nearly three-fourths of the universe’s mass and energy.
    Cellex-C Serum

  20. #20 galvanized tub
    August 3, 2010

    darkness doesnt exist ! it is merely the absence of light!

  21. #21 sikander
    September 26, 2010

    i love these

  22. #22 funeral urns
    September 26, 2010

    As the Universe expands, it appears to create more space, and hence, more energy.

  23. #23 vegan protein powder
    October 21, 2010

    Yet for all their disdain for the former Alaska governor, liberals still can’t quite put their finger on her

  24. #24 pug training
    October 26, 2010

    Great list, I really enjoy reading these posts and I’ve already downloaded (and subsequently gotten hooked on) Drop7 based on your video game list.

  25. #25 Maternity Swimwear
    November 8, 2010

    Cool! That just makes sense for many’s minds, lol. We should be more optimistic in life.

  26. #26 Alycia
    November 11, 2010

    Hi Ethan,
    Love your “Macho Man Randy Savage” halloween costume. I saw a recent picture of Randy and he has completely white hair now, can you believe it!?

  27. #27 SPSS Help
    November 13, 2010

    You have a good money if you make a lot of tourist want to visit your town. To make them want to visit your town, you need to make sure that you have the clean town area. There are no people that want to go toi a dirty place like this.

  28. #28 movers new york
    November 30, 2010

    Their government know if they can manage that potential change by their own. That is why they need people that have some experience to help them and we can stay in their country for free.

  29. #29 Roy Mendez
    December 3, 2010

    it shouldnt be called “DARK” its actually more “Light” than dark in fact its so clear its transparant. The first cosmologists missed the opportunity to coin it properly and put the wrong spin on it. Imagine if it was first coined white matter or even golden matter or god forbid … holy matter

  30. #30 Helosboing
    December 22, 2010

    This is the application project. They need to make a good one to make sure that tou have alot of people that will use this application. More people mean we sucess in this project. bingo

  31. #31 Jacky
    January 15, 2011

    Development of this idea might start to look like “steady state” with STD Symptoms the source of the expansion being an inherent property of space rather than Fred Hoyles sartirical Big Bang?

  32. #32 Yachtfinder
    January 21, 2011

    yeah… good point.. why is it called “dark”?:)

  33. #33 zahnarzt
    January 25, 2011

    hm.. funny thing… i’ve heard that in physics, light is synonym with energy, but this doesn’t sound ok: dark light… light is bright, not dark :)

  34. #34 crd2
    January 26, 2011

    The term “dark” refers to how much we know about it. Just as to illuminate something can also mean to become more aware of, or learn more about something. (Example: To shed light on a topic). So dark just means that we know very little, not necessarily that it doesn’t give off any photons. I agree, the name is far from optimal. If we can down grade Pluto out of planetary status and have the collective world accept it, I don’t see any reason why changing the name of dark energy should be so difficult.

  35. #35 yachtcharter
    January 26, 2011

    @crd2 nice explanation of the dark term :) actually, we shouldn’t change it because it’s pretty nice and seems full of mystery:)

  36. #36 wastewater mangement
    February 4, 2011

    I think you are trying to prove something new in the field of energy. Actually we can not imagine any kind of energy without the photon packet.

  37. #37 avril
    February 23, 2011

    THIS IS AWESOME!!

  38. #38 hued
    February 24, 2011

    Wouldn’t it be possible for a particle to travel _faster_ then light if it some how had negative mass? (yes i know, it may be silly physically but come on the math works doesn’t it?), I’m pretty sure this would also mean it traveled in the reverse direction in time but i haven’t played with the relativity equations enough yet to be sure.

    i-tunes download

  39. #39 Mario
    April 5, 2011

    I agree, the name is far from optimal. If we can down grade Pluto out of planetary status and have the collective world accept it, I don’t see any reason why changing the name of dark energy should be so difficult.
    This is the application project. They need to make a good one to make sure that tou have alot of people that will use this application.
    alivesite

  40. #40 Geremy
    April 6, 2011

    I think this is likely to produce anything new? No, probably not. There are many good reasons to believe that we know what we’re talking about, but that doesn’t really matter. What matters is that Cherished Teddies

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    June 18, 2011

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    July 14, 2011

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