Wikipedia:Reference desk/Archives/Science/2015 April 17

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April 17

Space having mass

So, does space itself have mass? (Please try to answer in simple term because I'm not too swift when it comes to this sort of thing.) Anna Frodesiak (talk) 00:36, 17 April 2015 (UTC)

It's a tough question to answer. Strictly speaking, no, space doesn't have mass. Space is a property, and mass is a property, and saying "does space have a mass" is akin to asking "does color have a taste?". It's pretty nonsensical. Now, if you're saying "Does a perfect hard vacuum have a mass" (a hard vacuum being basically the closest we can get to empty space) the answer is yes. Because there is such a thing as vacuum energy, and energy and mass are two words for the same thing, then empty space still has mass in it. The space itself of course doesn't have a mass anymore than blue has a taste. But the space does contain energy, and energy is mass. --Jayron32 00:57, 17 April 2015 (UTC)

Depends on the definition. A certain volume of space has a certain volume of vacuum energy. That energy has a certain mass. Since the energy is balanced, positive and negative, the mass "cancels out". But if one takes the absolute value, it is a positive figure. μηδείς (talk) 01:35, 17 April 2015 (UTC)

Are you thinking of the concept of Negative mass? Dbfirs 17:45, 17 April 2015 (UTC)

What about "Is space stuff?" I mean, is it something, as compared to nothing? Anna Frodesiak (talk) 02:01, 17 April 2015 (UTC)

Space is definitely something. It is our current understanding that it came into existance at a certain point in time, before which it did not exist. Vespine (talk) 04:30, 17 April 2015 (UTC)

Well, if it's definitely something as compared to nothing, then it must be something, if you see what I mean. Anna Frodesiak (talk) 06:23, 17 April 2015 (UTC)

I recommend reading (or perhaps skimming it since it contains a mixture of technical jargon and layman quotes) the article about Einstein's resolution to the Hole argument in which he concludes that spacetime exists only in relation to the existence of matter. --Modocc (talk) 07:01, 17 April 2015 (UTC)

This follow-up question reminds me of a description of what existed "before" the big bang or "outside" the universe in a book about the evolution of the universe for high school students. It called it a nothingness so profound it defies human comprehension. So, yes; it is something compared to nothing, but you have to evaluate your concept of nothing to grasp that what space has that nothing doesn't. Handschuh-^{talk to me} 09:06, 17 April 2015 (UTC)

Dark matter figures in here. Dark matter seems to exist in space, concentrated along with visible matter, so mainly near galaxies. We can only detect it based on it's gravitational effects, as otherwise it is invisible. But a gravitational effect implies it has some type of mass. Now, whether dark matter is something separate from space or a property of space, that we don't really know. StuRat (talk) 07:39, 17 April 2015 (UTC)

Actually, we have a fairly good idea that dark matter is not a property of space, because we can observe that a) it's normally associated with visible matter, but is some cases can be separated from it. That would be hard to explain if it would be a feature space itself. This may be different for dark energy, which, despite the similar name, is very different. --Stephan Schulz (talk) 07:46, 17 April 2015 (UTC)

Just to let you all know, I am digesting and reading up on the links you've provided. My intuition tells me that space itself is the missing stuff. I bet in 100 years, they'll figure that out. You see, intuition always beats logic, except with the stock market, in criminal law, choosing medication, and a few other areas. :) Anna Frodesiak (talk) 11:41, 17 April 2015 (UTC)

Check A Universe from Nothing and be sure to youtube Krauss' debates and discussions on "nothing". This is hotly debated - for example, does a vacuum really contain nothing or do its quantum fields comprise something? There are also wildly varying estimates as to the total amount of dark matter/energy in the universe, so it's anybody's guess at the moment, as it is with anything else in theoretical physics. To me, the best mathematical definition of "nothing" is a set without any elements, not even zeroes or nulls. So, is there an area in space without matter, energy and gravitational fields? If so then that would constitute a void/nullity or "nothing" but I doubt an area like that can exist in our universe (except maybe in the brains of some politicians). Sandman1142 (talk) 12:46, 17 April 2015 (UTC)

I have some ignorant suspicions about vacuum energy. I started with, the holographic universe model has put forward the idea that fundamental properties of space like the maximum amount of matter in a region before a black hole is formed, or the maximum entropy possible, depend on the square instead of the cube; why then does vacuum energy depend on the cube? But then there's a more basic issue: if you can ignore infinities with vacuum energy, saying only differences in energy are measurable, then why is some finite expectation value of it supposed to be meaningful? And then, the article appeals to virtual particles, but as discussed recently above, the Casimir effect explanation by this means is going out of vogue. I vaguely recollect it being possible likewise to dispense with virtual particles at the event horizon, by postulating quantum tunneling out of the hole. They seem like an unconvincing bookkeeping game gone wild, and so I don't see how they are "proof" of vacuum energy. And then, to top it all off, dark energy is apparently subject to a basic experimental problem that the supernovae aren't constant after all [1]. Wnt (talk) 15:41, 17 April 2015 (UTC)

Virtual particles have never been important to Hawking radiation. Hawking's original paper derived the result without using virtual particles.

The research described in that press release smells bad for a couple of reasons. First, it's good to be leery of press releases in general, because if the research was actually important it wouldn't need the university PR department to advertise it. Second, several unrelated data sets point to a large value of Ω_Λ (the fraction of dark energy). See e.g. this chart, or the WMAP team's estimates of Ω_Λ with and without supernova data.

When people say that only energy differences are measurable, they're talking about some theory without gravity. Nobody wants to subtract infinities, but it has helped in the past (renormalization in the early days). The idea is that for now you don't know how to calculate this thing correctly, but at least this handwavy argument suggests that there is a calculable answer in there. That said, no one knows how to "calculate" the vacuum energy even by subtracting infinities, except back when it was thought to be zero, and the argument was basically that ∞ − ∞ = 0.

A constant energy density means a constant spacetime curvature. If you imagine gluing little pieces of curved space together, you'll get increasingly large portions of a sphere (whose radius is the radius of curvature of the little pieces of space). When you get to a hemisphere, that's the Schwarzschild limit. Even though it's in some sense the boundary that sets the limit, it's still geometrically natural to distribute curvature evenly over the interior. For the observed cosmological constant, the radius of curvature is (from memory) about 18 billion light years. -- BenRG (talk) 21:45, 17 April 2015 (UTC)

I think the best answer to the original question is no, space doesn't have mass. The question seems to be about the basic physical concepts of space and mass, and basically space doesn't have mass. Even if there's some sort of vacuum mass/energy, either it's a cosmological constant, which is arguably not mass, or it's a field like the Higgs field, in which case it's that field that has the mass, not space as such. -- BenRG (talk) 21:45, 17 April 2015 (UTC)

I think that's the point I was trying to make. People seem to confuse properties of stuff with the stuff itself. Matter (the sciency word for "stuff") is often defined as "that which takes up space and has mass". Space, mass, energy, etc. are all properties that matter possesses and are not separate "stuff" different than matter. When we speak of properties of an object, we talk about its texture, its taste, its color, its smell, etc. Mass, energy, and space are similarly properties of objects, not properly "stuff" unto themselves. It's why questions like this are ultimately nonsensical. One property does not "have" another property. As I noted above, just as the color "blue" doesn't have a taste, space cannot have a mass. --Jayron32 01:25, 18 April 2015 (UTC)

Space(-time) cannot exist without mass. So no mass > no space. Trying to conceptualise 'no space' is difficult. There is nothing -- and nothing(even space) in which the nothingness exists. Therefore 'nothingness' is less than space-time with 'nothing' in it. So space time (even with nothing observable in it) is something more than 'nothing at all'. It is more because it contains mass that creates the space-time in the first place. I hope that is now clear to everyone.--BoldEditor (talk) 17:30, 18 April 2015 (UTC)

Thank you all for the thoughtful responses. :) Anna Frodesiak (talk) 22:46, 19 April 2015 (UTC)