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Why the Tiny Weight of Empty Space Is Such a Mystery
- crb002 9y agoWould relativity explain a lot of it? "Empty" space isn't always empty. You put a camera anywhere in the known universe and almost instantly it will get bombarded by particles. All those particles in flight, albeit sparse, have mass or in the case of photons can collide turning their energy into mass. TLDR. What is the mass of all in flight particles?
- matte_black 9y agoNo, even empty space, where there is not even one particle or even the thought of anything aspiring to be a particle within the defined area, will have a tiny weight.
- wodenokoto 9y agoBut don't particles and anti-particles form everywhere constantly? Won't they add a temporary weight, before cancel out?
- mikhailfranco 9y agoThe Cosmic Microwave Background (CMB) has ~420 photons/cm^3 each with 24 meV, so about 10 MeV/m^3. The Cosmic neutrino Background (CvB) has ~340 neutrinos/cm^3 each with 50 meV, so about 17 MeV/m^3. As a comparison, the visible matter (baryon) density is estimated to be 1/5 protons/m^3, each with 940 MeV, so about 240 MeV/m^3.
- ythn 9y ago> This fine-tuned situation suggests that there might be a huge number of universes, all with different doses of vacuum energy, and that we happen to inhabit an extraordinarily low-energy universe because we couldn’t possibly find ourselves anywhere else. At a certain point "God" is going to be a simpler explanation than "infinite universes with infinite cosmological constant variance", etc.
- matte_black 9y agoOr for some, “simulation”.
- pdabbadabba 9y agoWell, this depends on your conception of simplicity. It certainly makes for a shorter explanatory sentence, but at the cost of undermining our ability to truly explain anything at all, since we cannot know whether a given result is due to the laws of nature or is a miracle--or both. And if it's a miracle, we have no reliable access to its reasons for occurring.
- namelost 9y agoWhen physicists (and you guys know who you are!) say things like "the universe arose from an infinite multiverse", they are bullshitting, because structure does not come from "infinity", structure comes from rules (which may generate some structure that is infinite), and if you can't say anything about the rules then the answer is simply "I don't know".
- pdabbadabba 9y ago> structure does not come from "infinity", structure comes from rules I can't say I understand this statement, but I'll venture this friendly amendment: explanations come from rules, or at least a method of description that allows us to say why result A obtained and not result B. (Or maybe an explanation that the process was random, and therefore that this part of the process cannot be explained.) So I think the problem--if there really is one--is with the word "arose" in your sentence, not "infinite." I can see no problem with invoking the infinite in a useful explanation (note that theists do this all the time!), but I can see a problem with having no account of why our universe "arose" and not some other one. Of course, I think that just about every physicist would be happy to admit this! (Those that don't think they have an answer, that is--possibly involving the anthropic principle.) After all, answering questions is their job, so acknowledging an unknown is just the beginning of a research agenda, not an admission of defeat.
- 9y ago
- klank 9y ago> Force fields have positive zero-point energies while matter fields have negative ones This tidbit stuck out to me. Anybody able to offer a deeper explanation of why?
- cammikebrown 9y agoThat's an explanation proposed for why we can barely measure any gravity stemming from the huge energy contained in the zero-point field. The idea is that the fermion field (matter) and the boson field (energy) cancel each other out. This theory is part of supersymmetry.
- auntienomen 9y agoThis answer is slightly misleading. Fermionic fields have negative vacuum energy, while bosonic ones have positive. This is an basic fact of quantum field theory, a consequence of Lorentz invariance and Fermi-Dirac statistics (resp. Bose-Einstein statistics). Supersymmetry makes use of this fact: When the bosons and fermions come in pairs, their vacuum energies can cancel because they have opposite sign. But the association of minus signs to fermions and plus signs to bosons is older and more elementary than supersymmetry.
- auntienomen 9y agoI wish I had an elementary conceptual explanation for why this association exists. It's a simple calculation, but hard to describe without resorting to equations. Maybe the best I can say is that when one writes down the energy function for a quantum mechanical system of many particles, it has a form which is _strongly_ constrained by special relativity. The variables which describe the creation of particles are perfectly paired with the variables which describe the annihilation of particles. For bosons, these variables commute, just like ordinary functions. For fermions, these variables anti-commute, picking up a sign when you exchange them. If you repeatedly exchange these variables to rewrite energy function as vacuum energy + energy of 1 particle + energy of 2 particles + ...., you discover that the fermions contribute negatively to the vacuum energy while bosons contribute positively.
- thriftwy 9y agoThere are a lot of states of vacuum. Our space is either in rock bottom stable state or in metastable one. Maybe it's just the state in which this energy is as small as it gets?
- pixl97 9y agoAt least we hope so https://en.wikipedia.org/wiki/False_vacuum#Vacuum_metastability_event https://en.wikipedia.org/wiki/False_vacuum#Vacuum_metastabil...
- joe_the_user 9y agoThe argument for multiple-worlds seems to be that if you take the most elegant possible formulation of the "equations of the universe", you find that some of constants in these equation have to be set to apparently arbitrary values to imply a universe like our own. This seems to rest on an assumption that simple patterns tend to continue beyond our immediate perception, like if a person see a part of a sphere sticking out of the sand on a beach, they would tend to expect an entire sphere to buried beneath. The two questions that appear would: is formulation really the simplest and does this kind of reasoning apply "outside the universe", given the universe is all that we use to make such judgments.
- zitterbewegung 9y agoThis is using the Anthropic principle to argue the point for the many worlds hypothesis because it is being argued that life is so fragile that it could not have formed without certain constants being how they were. So that there must have been a bunch of other realities that failed in creating sentient life. The constants would apply outside the universe because the constants are invariant other all of our observations (the fine structure constant is an observed number and its value is arbitrary and if it was greater or less than it we wouldn't exist). But they aren't part of our perception they are part of our measurements.
- joe_the_user 9y agoThis is using the Anthropic principle to argue the point for the many worlds hypothesis because it is being argued that life is so fragile that it could not have formed without certain constants being how they were. So that there must have been a bunch of other realities that failed in creating sentient life. I don't think the existence or non-existence of sentient life in alternate universe is in anyway necessary for the argument. If we assume possible universes is a set parameterized by a constant C and if we know only value X gives a universe with the properties we observe, we can deduce C = X. If a value Y yields a universe with sentients that can't be us, we still know that isn't our universe and so we know C!=Y.
- deleted 9y ago
- woodandsteel 9y agoI really like this article. I have read a lot of articles that bandy about terms like dark energy, the cosmological constant, and the multiverse. This was the first thing I have read that clearly explains how they link together. However, I have a question. The article says that dark energy "presence causes the cosmos to expand ever more quickly, since, as it expands, new space forms, and the total amount of repulsive energy in the cosmos increases" But wouldn't this violate the first law of thermodynamics?
- chowells 9y agoIt wouldn't violate thermodynamics in any meaningful way unless you could actually use that increased energy to produce work. Every formulation of thermodynamics I was able to find is specifically about deriving work from differences in energy.
- woodandsteel 9y agoSee my response to SAI_Peregrinus above.
- tzs 9y agoThis post on Steve Carroll's blog [1], called "Energy Is Not Conserved", answers that question fairly clearly. [1] http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ http://www.preposterousuniverse.com/blog/2010/02/22/energy-i...
- woodandsteel 9y agoThank you, that link answers my question.
- SAI_Peregrinus 9y agoThe laws of thermodynamics only hold for closed (finite) systems. The observable universe is finite, but may not be closed (expansion from dark energy). The total universe may be infinite. In either case the laws of thermodynamics don't necessarily apply.
- hateful 9y agoThis is totally based on zero evidence, but it seems to me, as a casual observer, that maybe there are elementary particles whizzing aren't detectable until they combine with other elementary whizzing particles and combine to make the detectable ones? So like hydrogen can be fused into helium (I know, easier said than done!), sometimes the they collide and create a detectable particle. This explains the Casimir effect in that there really wasn't nothing between the plates, just the stuff whizzing through the plates that we can't block.
- comboy 9y agoAFAIK the only particles that appear out of nowhere (which would in your view happen when those non-detectable particles collide) are particle-antiparticle pairs[1]. It does explain the Casimir effect. 1. https://en.wikipedia.org/wiki/Quantum_fluctuation https://en.wikipedia.org/wiki/Quantum_fluctuation
- Veelox 9y agoQuestion, if assuming a multiverse to explain the exactness of the cosmological constant is a defensible position, is there any reason not to consider the deist view and say the universe was created with the cosmological constant needed for life to form as an equally likely outcome?
- gloriousduke 9y agoA deist creator explanation is equally untestable, but is probably less parsimonious than a multiverse explanation.
- sa46 9y agoWhat does "less parsimonious" mean in this context? The definition has "unwilling to spend money or use resources; stingy or frugal" but I'm not sure what you're describing as less frugal. Is it a way of saying the deist explanation is more likely?
- mdorazio 9y agoI think in this context it means that adding a deity into the explanation is adding an unnecessary extra element where none is needed. Thus the explanation is less "frugal" than one where we assume a multiverse without any creator(s).
- incompatible 9y agoThe difficulty for any theory is explaining why anything exists at all, i.e., if there's no space and no time, isn't that a stable state? Without time, how could anything ever happen? If a multiverse theory could give a way to get a universe out of nothing, it would be a lot more elegant than a deity theory. The deity theory after all is incomplete, it just supposes that our universe is embedded inside some sort of "outer" universe where deities live, but that outer universe also has to be created somehow.
- glenstein 9y ago
- chmike 9y agoThe Space Time Quantization theory of Prof. Auguste Meessen [1] leads to an explanation of the accelerating expansion of the universe, the cosmological constant suggested by Einstein (drak energy) and dark matter. It uses just simple and basic physics. The only new hypothesis leading to this theory is that measured distances would be quantified. That means that there would be a minimal measurable length. [1] http://www.scirp.org/journal/Articles.aspx?searchCode=Auguste++Meessen&searchField=authors_complete&page=1&SKID=0 http://www.scirp.org/journal/Articles.aspx?searchCode=August...