Simply typed lambda calculus: Difference between revisions

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In [[physics]], there is a '''speculative''' notion that if there were a [[black hole]] with the same mass and charge as an [[electron]], it would share many of the properties of the electron including the [[electron magnetic dipole moment|magnetic moment]] and [[Compton wavelength]]. This idea is substantiated within a series of papers published by Albert Einstein between 1927 and 1949. In them, he showed that if elementary particles were treated as singularities in spacetime, it was unnecessary to postulate [[Geodesic (general relativity)|geodesic]] motion as part of general relativity.<ref>{{cite journal | last1=Einstein | first1=A. |authorlink1=Albert Einstein | last2=Infeld | first2=L. | authorlink2=Leopold Infeld | last3=Hoffmann | first3=B. | authorlink3=Banesh Hoffmann | title=The Gravitational Equations and the Problem of Motion | journal=[[Annals of Mathematics|Annals of Mathematics. Second Series]] | volume=39 | issue=1 |date=January 1938 | pages=65–100 | jstor=1968714 |doi=10.2307/1968714}}</ref>


==Problems==
Quantum mechanics permits superluminal speeds for an object with as small a mass as the electron over distance scales larger than the Schwarzschild radius of the electron.{{Citation needed|date=August 2011}}


==Schwarzschild radius==
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The [[Schwarzschild radius]] (''r<sub>s</sub>'') of any mass is calculated using the following formula:
:<math>r_s = \frac{2Gm}{c^2}</math>
 
For an electron,
 
:''G'' is Newton's [[gravitational constant]],
:''m'' is the mass of the [[electron]] = {{val|9.109|e=-31|u=[[kilogram|kg]]}}, and
:''c'' is the [[speed of light]].
 
This gives a value
 
:''r<sub>s</sub>'' = {{val|1.353|e=-57|u=m}}.
 
So if the electron has a radius as small as this, it would become a gravitational singularity. It would then have a number of properties in common with black holes. In the [[Reissner–Nordström metric]], which describes electrically charged black holes, an analogous quantity ''r<sub>q</sub>'' is defined to be
 
:<math>
r_{q} = \sqrt{\frac{q^{2}G}{4\pi\epsilon_{0} c^{4}}}
</math>
 
where ''q'' is the charge and ''ε''<sub>0</sub> is the [[vacuum permittivity]].
 
For an electron with ''q'' = −[[elementary charge|''e'']] = {{val|-1.602|e=-19|u=[[coulomb|C]]}}, this gives a value
 
:''r<sub>q</sub>'' = {{val|9.152|e=-37|u=m}}.
 
This value suggests that an electron black hole would be [[extremal black hole|super-extremal]] and have a [[naked singularity]]. Standard [[quantum electrodynamics]] (QED) theory treats the electron as a point particle, a view completely supported by experiment. Practically, though, particle experiments cannot probe arbitrarily large energy scales, and so QED-based experiments bound the electron radius to a value smaller than the [[Compton wavelength]] of a large mass, on the order of {{val|e=6|u=GeV}}, or
 
:<math>r \approx \frac{\alpha \hbar c}{10^6 GeV} \approx 10^{-24} m</math>.
 
No proposed experiment would be capable of probing ''r'' to values as low as ''r<sub>s</sub>'' or ''r<sub>q</sub>'', both of which are smaller than the [[Planck length]].  Super-extremal black holes are generally believed to be unstable.  Furthermore, any physics smaller than the [[Planck length]] probably requires a consistent theory of [[quantum gravity]].
 
==See also==
* [[Quantum gravity]]
* [[Extremal black hole]]
* [[Geon (physics)]]
* [[Ring singularity]]
 
==References==
{{reflist}}
 
==Further reading==
{{refbegin}}
* {{cite paper | last=Burinskii | first=A. | year=2005 | arxiv=hep-th/0507109 | title=The Dirac–Kerr electron|bibcode = 2008GrCo...14..109B |doi = 10.1134/S0202289308020011 }}
* {{cite paper | last=Burinskii | first=A. | year=2007 | arxiv=0712.0577 | title=Kerr Geometry as Space–Time Structure of the Dirac Electron|bibcode = 2007arXiv0712.0577B }}
* {{cite paper | last=Duff | first=Michael | authorlink = Michael Duff (physicist) | year=1994 | arxiv=hep-th/9410046| title=Kaluza–Klein Theory in Perspective|bibcode = 1995okml.book...22D }}
* {{cite journal | last=Hawking | first=Stephen | authorlink=Stephen Hawking | year=1971 | title=Gravitationally collapsed objects of very low mass | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=152 | page=75 | bibcode=1971MNRAS.152...75H}}
* {{cite book | last=Penrose | first=Roger | authorlink=Roger Penrose | year=2004 | title=[[The Road to Reality: A Complete Guide to the Laws of the Universe]] | location=London | publisher=Jonathan Cape}}
* {{cite book | last=Salam | first=Abdus | authorlink=Abdus Salam | chapter=Impact of Quantum Gravity Theory on Particle Physics | editor1-last=Isham | editor1-first=C. J. | editor2-last=Penrose | editor2-first=Roger | editor3-last=Sciama | editor3-first=Dennis William | title=Quantum Gravity: an Oxford Symposium | publisher=Oxford University Press}}
* {{cite journal | last='t Hooft | first=Gerard | authorlink=Gerard 't Hooft | year=1990 | doi=10.1016/0550-3213(90)90174-C | title=The black hole interpretation of string theory | journal=[[Nuclear Physics B]] | volume=335 | pages=138–154|bibcode = 1990NuPhB.335..138T }}
* {{cite paper | last=Murdzek | first=R. | journal=[[International Journal of Modern Physics D]] | volume=16 | issue=4 | pages=681–686 | year=2007 | doi=10.1142/S0218271807009826 | bibcode=2007IJMPD..16..681M | title=The Geometry of the Torus Universe | postscript=, }} which is related to "Hierarchical Cantor set in the large scale structure 3 with torus geometry".
{{refend}}
 
=== Popular literature ===
* [[Brian Greene]], ''[[The Elegant Universe|The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory]]'' (1999), ''(See chapter 13)''
* [[John A. Wheeler]], ''[[Geons, Black Holes & Quantum Foam]]'' (1998), ''(See chapter 10)''
 
{{black holes}}
 
[[Category:Black holes]]
[[Category:Quantum gravity]]
[[Category:Hypothetical elementary particles]]

Latest revision as of 18:10, 23 November 2014


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