Turnstile (symbol): Difference between revisions
Jump to navigation
Jump to search
en>Cydebot m Robot - Moving category Logical symbols to Category:Logic symbols per CFD at Wikipedia:Categories for discussion/Log/2012 February 15. |
en>Phil Last |
||
| Line 1: | Line 1: | ||
The name of the | [[File:Observable Universe with Measurements 01.png||right|300px|thumb|Visualization of the three-dimensional [[large-scale structure of the universe]] in the Hubble volume. The scale is such that the fine grains of light represent collections of large numbers of [[supercluster]]s. The [[Virgo Supercluster]] - home of [[Milky Way|our own galaxy]] - is at the center of our Hubble volume, but is too small to be seen in the image.]] | ||
In [[Physical cosmology|cosmology]], a '''Hubble volume''', or '''Hubble sphere''', is a spherical region of the [[Universe]] surrounding an observer beyond which objects recede from that observer at a rate greater than the [[speed of light]] due to the expansion of the Universe.<ref name=Harrison>{{cite book |title=Masks of the Universe |url=http://books.google.com/?id=tSowGCP0kMIC&pg=PA206 |page=206 |author= Edward Robert Harrison |year=2003 |publisher=Cambridge University Press |isbn=0-521-77351-2}}</ref> | |||
The [[comoving distance|comoving]] radius of a Hubble sphere (known as the Hubble radius or the [[Hubble length]]) is <math>c/H_0</math>, where <math>c</math> is the [[speed of light]] and <math>H_0</math> is the [[Hubble constant]]. The surface of a Hubble sphere is called the ''microphysical horizon'',<ref name= Montani>{{cite arxiv |title=Study of the Quasi-isotropic Solution near the Cosmological Singularity in Presence of Bulk-Viscosity |author= N. Carlevaro & G. Montani |arxiv=0711.1952 |year=2009}}</ref> the ''Hubble surface'', or the ''Hubble limit''. | |||
More generally, the term "Hubble volume" can be applied to any region of space with a volume of order <math>(c/H_0)^3</math>. | |||
However, the term is also frequently (but mistakenly) used as a [[synonym]] for the [[observable universe]]; the latter is larger than the Hubble volume.<ref name= Davis>For a discussion of why objects that are outside the Earth's Hubble sphere can be seen from Earth, see {{cite arxiv |title=Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe |author= TM Davis & CH Linewater |arxiv=astro-ph/0310808 |year=2003}}</ref><ref>For an example of mistaken usage, see {{cite book |author=Max Tegmark |authorlink=Max Tegmark |chapter=Parallel Universes |title=Science and Ultimate Reality: From Quantum to Cosmos |editor-last=Barrow |editor-first=J. D. |editor2-last=Davies |editor2-first=J. D. |editor3-last=Harper |editor3-first=C. L. |pages=459''ff'' |publisher=Cambridge University Press |year=2004 |isbn=0-521-83113-X |url=http://books.google.com/?id=K_OfC0Pte_8C&pg=PA459}}</ref> | |||
==Relationship to age of the universe== | |||
The Hubble length <math>c/H_0</math> is 14 billion light years in the [[Lambda-CDM model|standard cosmological model]], somewhat larger than <math>c</math> times the [[age of the universe]], 13.8 billion years. This is because <math>1/H_0</math> gives the age of the universe by a backward extrapolation which assumes that the recession speed of each galaxy has been constant. However, modern observations indicate recession speeds are increasing slightly<ref name=Tonry>{{cite journal |title=Cosmological Results from High-z Supernovae |year=2003 |arxiv=astro-ph/0305008 |author=John L Tonry |journal=Astrophys J |volume=594 |bibcode = 2003ApJ...594....1T |doi = 10.1086/376865 |author-separator=, |display-authors=1 |last2=Schmidt |first2=Brian P. |last3=Barris |first3=Brian |last4=Candia |first4=Pablo |last5=Challis |first5=Peter |last6=Clocchiatti |first6=Alejandro |last7=Coil |first7=Alison L. |last8=Filippenko |first8=Alexei V. |last9=Garnavich |first9=Peter |pages=1 }}</ref> due to [[dark energy]], so that <math>1/H_0</math> is only an approximation to the [[age of the universe]]. | |||
==Hubble limit as an event horizon== | |||
Objects at the Hubble limit have an average comoving speed of ''c'' relative to an observer on the Earth so that, in a universe with constant [[Hubble parameter]], light emitted at the present time by objects outside the Hubble limit would never be seen by an observer on Earth. | |||
That is, Hubble limit would coincide with a cosmological [[event horizon]] (a boundary separating events visible at some time and those that are never visible<ref name=Harrison2>{{cite book |author=Edward Robert Harrison |page=439 |url=http://books.google.com/?id=-8PJbcA2lLoC&pg=PA439 |title=Masks of the Universe |isbn=0-521-66148-X |publisher=Cambridge University Press |year=2000}}</ref>). | |||
However, the [[Hubble parameter]] is not constant in various cosmological models<ref name= Davis/> so that the Hubble limit does not, in general, coincide with a cosmological event horizon. For example in a decelerating [[Friedmann equations|Friedmann universe]] the Hubble sphere expands faster than the Universe and its boundary overtakes light emitted by receding galaxies so that light emitted at earlier times by objects outside the Hubble sphere still may eventually arrive inside the sphere and be seen by us.<ref name= Davis/> Conversely, in an accelerating universe, the Hubble sphere expands more slowly than the Universe, and bodies move out of the Hubble sphere.<ref name=Harrison/> | |||
Observations indicate that the universe is [[accelerating universe|accelerating]],<ref name="Tonry"/> so that some objects that we can currently exchange signals with will one day cross our Hubble limit. | |||
==See also== | |||
*[[Hubble's Law]] | |||
==References== | |||
{{reflist}} | |||
==External links== | |||
*[http://www.mpa-garching.mpg.de/Virgo/hubble.html The Hubble Volume Simulations] | |||
[[Category:Physical cosmology]] | |||
Revision as of 12:23, 30 January 2014
In cosmology, a Hubble volume, or Hubble sphere, is a spherical region of the Universe surrounding an observer beyond which objects recede from that observer at a rate greater than the speed of light due to the expansion of the Universe.[1]
The comoving radius of a Hubble sphere (known as the Hubble radius or the Hubble length) is , where is the speed of light and is the Hubble constant. The surface of a Hubble sphere is called the microphysical horizon,[2] the Hubble surface, or the Hubble limit.
More generally, the term "Hubble volume" can be applied to any region of space with a volume of order . However, the term is also frequently (but mistakenly) used as a synonym for the observable universe; the latter is larger than the Hubble volume.[3][4]
Relationship to age of the universe
The Hubble length is 14 billion light years in the standard cosmological model, somewhat larger than times the age of the universe, 13.8 billion years. This is because gives the age of the universe by a backward extrapolation which assumes that the recession speed of each galaxy has been constant. However, modern observations indicate recession speeds are increasing slightly[5] due to dark energy, so that is only an approximation to the age of the universe.
Hubble limit as an event horizon
Objects at the Hubble limit have an average comoving speed of c relative to an observer on the Earth so that, in a universe with constant Hubble parameter, light emitted at the present time by objects outside the Hubble limit would never be seen by an observer on Earth. That is, Hubble limit would coincide with a cosmological event horizon (a boundary separating events visible at some time and those that are never visible[6]).
However, the Hubble parameter is not constant in various cosmological models[3] so that the Hubble limit does not, in general, coincide with a cosmological event horizon. For example in a decelerating Friedmann universe the Hubble sphere expands faster than the Universe and its boundary overtakes light emitted by receding galaxies so that light emitted at earlier times by objects outside the Hubble sphere still may eventually arrive inside the sphere and be seen by us.[3] Conversely, in an accelerating universe, the Hubble sphere expands more slowly than the Universe, and bodies move out of the Hubble sphere.[1]
Observations indicate that the universe is accelerating,[5] so that some objects that we can currently exchange signals with will one day cross our Hubble limit.
See also
References
43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.
External links
- ↑ 1.0 1.1 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - ↑ Template:Cite arxiv
- ↑ 3.0 3.1 3.2 For a discussion of why objects that are outside the Earth's Hubble sphere can be seen from Earth, see Template:Cite arxiv
- ↑ For an example of mistaken usage, see 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - ↑ 5.0 5.1 One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting
In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang - ↑ 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534