Wikipedia:Reference desk/Archives/Science/2022 February 12

= February 12 =

Does drinking chlorinated water cause cancer?
My local water utility occasionally gives us a slug of extra chlorine, making my tap water smell like a swimming pool. Is there any science showing that drinking that water could be harmful?

Conflicting answers from the Internet:

https://www.cancerwa.asn.au/resources/cancermyths/chlorine-cancer-myth/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4824718/

https://www.scientificamerican.com/article/earth-talks-tapped-out/

03:06, 12 February 2022 (UTC)2600:1700:D0A0:21B0:D096:A2DF:EE0B:35D3 (talk)
 * You may wish to look at Monochloramine, one of the main things formed in the chlorination. It mentions cancer as a risk, and the references might tell you about testing and how much is safe. Graeme Bartlett (talk) 02:28, 13 February 2022 (UTC)
 * Being safe is often a relative thing. Drinking chlorinated tap water is generally safer than drinking unchlorinated water. People who worry about chlorinated water may do so while enjoying barbecued meat and beer, both linked with cancer. --Lambiam 14:04, 13 February 2022 (UTC)

Mass and curvature in General Relativity
In Einstein's theory of General Relativity, gravity is a fictional force arising from the curvature of spacetime. This curvature is said to be due to the presence of mass. But what is "mass"? Is it possible that what we call "mass" is actually nothing but this curvature, and that the conservation of mass is a geometric conservation of curvature? Thank you. Hevesli (talk) 12:52, 12 February 2022 (UTC)
 * It's worth noting that the conservation of mass doesn't quite hold up, since matter and energy are interchangeable on a quantum scale. nagualdesign 15:56, 12 February 2022 (UTC)
 * The lay-level (non-mathematical) explanation of General relativity says that the curvature of spacetime is caused by mass. If mass is the curvature, what would be causing this curvature?
 * In Quantum mechanics, it is similarly suggested at the lay level that mass is a quality imparted to matter by the Higgs boson and Higgs field via the Higgs mechanism. It is widely stated that at present the two theories or models, Relativity and Quantum mechanics, are incompatible even though each appears to be accurate within its own sphere of application and measurement. Your suggestion does not readily seem able to contribute to the reconciliation of the two. {The poster formerly known as 87.81.230.195} 90.193.130.191 (talk) 17:36, 12 February 2022 (UTC)
 * Thank you. It is not my purpose to reconcile these theories. Nor do I strive for the Theory of Everything with this idea. The fundamental nature of energy is probably even more mysterious than that of mass. I believe that heat is kinetic energy and chemical energy is potential energy. Using the relativistic mass formula, maybe we can equate kinetic energy with mass. Maybe a curvature of spacetime moving through space (in a stationary observer frame) causes additional curvature. And maybe a photon is accompanied by a curvature that moves with it. For other fields than the gravitational field the force is very local because at longer distances the positive and negative forces cancel each other out, but perhaps all forces are accompanied by curvature, only the effect is so local that it has not been observed yet. My question is really not whether I am correct, but whether this idea or similar ones have ever been considered. Could they not be a basis for theories with experimentally testable prediction? Hevesli (talk) 13:52, 13 February 2022 (UTC)
 * Photons absolutely can curve spacetime just via their inherent kinetic energy. See Kugelblitz (astrophysics).  In General Relativity, it's not that "mass = curvature", it's that "mass = energy" and "energy causes curvature".  Mass is just energy that is bound up in the interactions that are matter.  It's far trickier to get photons into the same volume of space long enough to generate enough curvature to trap them, but there's nothing in the theory that says they can't.  In ordinary matter, that energy is mostly doing things like holding the atomic nucleus together, though small amounts of it are holding electrons around the atoms, or holding atoms to each other in compounds.  Another small fraction is involved in the Higgs mechanism.  But its all energy.  And it curves spacetime.  As an aside, the kind of curvature that causes gravity is mostly in the time dimension.  this video does a good job explaining it for a layperson. -- Jayron 32 21:37, 13 February 2022 (UTC)
 * Can I then rephrase the OP's question as follows:
 * Is it possible that what we call "energy" is actually nothing but this curvature, and that the conservation of energy is a geometric conservation of curvature?
 * Thank you :). --Lambiam 10:32, 14 February 2022 (UTC)
 * In a way this is the very heart of general relativity. The Einstein field equations equate the energy-momentum tensor to the Einstein tensor that describes the geometry of space-time. Everything that holds for the energy-momentum tensor holds for the Einstein tensor and vice versa, and this is in particular true for the continuity equation $$T^{\alpha\beta}_{\;\;;\beta} = 0$$ which embodies the conservation laws for energy and momentum, so that a similar continuity equation holds for the geometric tensor, $$G^{\alpha\beta}_{\;\;;\beta}=0$$.  In fact, GR – the Einstein tensor and the field equations – was constructed such that this holds (see Einstein_field_equations, even if you don't follow the math). Conservation of energy and momentum is an empirical fact that needed to be in GR, and the mathematical structure of GR followed from that. This does not mean that "curvature" and "energy" (to use simpler terms) are the same, just that they are intimately related (mass and energy are not the same thing either...). There's also Noether's theorem in there, which relates conservation laws to symmetries of space and time. --Wrongfilter (talk) 12:23, 14 February 2022 (UTC)