Path: csiph.com!eternal-september.org!feeder.eternal-september.org!weretis.net!feeder1.news.weretis.net!news.solani.org!.POSTED!not-for-mail From: Thomas 'PointedEars' Lahn Newsgroups: sci.physics,sci.physics.relativity Subject: Re: What is mass? Followup-To: sci.physics.relativity Date: Sat, 26 Sep 2015 08:35:23 +0200 Organization: PointedEars Software (PES) Lines: 84 Message-ID: <2280480.8StNvuNZVT@PointedEars.de> References: Reply-To: Thomas 'PointedEars' Lahn Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8Bit X-Trace: solani.org 1443249325 11521 eJwFwYEBwCAIA7CXdNDCzkGw/59gAuNmhxN0CGK2++XZvEfmd4qF/iXrUMpyGsvnQytKSw8zJhIy (26 Sep 2015 06:35:25 GMT) X-Complaints-To: abuse@news.solani.org NNTP-Posting-Date: Sat, 26 Sep 2015 06:35:25 +0000 (UTC) User-Agent: KNode/4.14.2 X-User-ID: eJwFwYEBACAEBMCVCE/jvMr+I3QXBsVJR8BjYsrJI9JtAx3m5lpHIXZnJ93Yt+BUkVl8069btlRY0/AqP2ZxFgI= Cancel-Lock: sha1:kMC4YKWqzGyifluVPXOJlBigHMg= X-NNTP-Posting-Host: eJwFwQEBwCAMAzBLBdbSyTmw+ZfwhEtDd4eoYLMBK0zcvPTn5ivM1zsrNdJ1lh2A6syHgfwBCXQQVA== Xref: csiph.com sci.physics:523242 sci.physics.relativity:365311 [X-Post sci.physics, sci.physics.relativity; F'up2 ] Fabian Russell wrote: > On Wed, 23 Sep 2015 19:12:18 +0200, Poutnik wrote: >> cannot be completely wrong equation. > > The equation is wrong because it specifies mass, m, as *the* mass, > i.e. the definitive mass or the one-and-only mass. There is only mass. To answer the question in the Subject header field value: Mass is a measure of the energy content of a body at rest in the laboratory frame (of reference): E = √(pc)² + (mc²)²) → m = E∕c² for p = 0, with p = γmv (relative rest → γ = 1, v = 0). That is why we build huge machines to *accelerate* subatomar particles close to the speed of light in vacuum, and have them collide with each other to create particles with a lot of mass and, more recently, to "produce" energy through nuclear fusion. > Correctly written, the *inertial* mass must be indicated because, > as already stated, there are two different "kinds" of mass. Two terms for the same thing is not how science works. > For some reason, the concepts of inertial mass and gravitational > mass have been effectively purged from physics, Because physics is a science. Superfluous terms are not used in science. One uses different terms for different things, the same term for the same thing. > but they are still valid. Because you say so? > GR *assumes* the equivalence of both types Because it can be *demonstrated*. Read on the elevator experiment: Without additional information, you cannot tell whether you are far away from a source of gravity or in free fall, and you cannot tell whether you are accelerating or near a source of gravity. (Einstein is often described as a theoretical genius only. But, in fact, the text of his works shows that he was deeply guided by experiment. And there is other evidence: He co-designed and had built an observatory [the Einsteinturm in Potsdam, Germany] only for testing GR. And he would have thrown out GR like yesterday’s newspaper if it had given the wrong result for the precession of the perihelion of Mercury. Just as he wrote [in German] “then away with the cosmological term” regarding his field equations when Hubble’s observations confirmed Lemaître’s theory that the universe was in fact not static, but expanding.) > and perhaps for this reason all textbooks incorrectly mention only a > single type of mass. But, as also mentioned, GR is not yet universally > established. In crackpot’s heads, perhaps. Everywhere else it is, quite literally, “universally” established, for example: - in timekeeping (precise clocks are gauged based on their elevation; it can be demonstrated that those at higher elevation tick faster than their same-model counterparts at lower elevation) - in communication (with orbital spacecraft and interplanetary probes); * as a special case, in satellite navigation (GPS and alternatives) (again, clocks close to a massive body tick slower than those farther away from it) - in astronomy and astrophysics (perihelion precession, gravitational lensing, black holes) - in cosmology (the ΛCDM, or *standard* model of cosmology) PointedEars -- “Science is empirical: knowing the answer means nothing; testing your knowledge means everything.” —Dr. Lawrence M. Krauss, theoretical physicist, in “A Universe from Nothing” (2009)