Hubblen laki ym. Hubblen ...

Edwin Powell Hubble (1889-1953)
kuva wikimedia

Tämä alkaa mennä melko hankalaksi, mutta koetetaan selviytyä apuneuvojen avulla.

Ensin asiantuntijoiden tekstiä wikistä, joka saa minut vikisemään ja sitten maallikon "käännös" eli ajatusta tekstistä:

Hubble's law

is the name for the observation in physical cosmology that

• objects observed in deep space (extragalactic space, ~10 megaparsecs or more) are found to have a Doppler shift interpretable as relative velocity away from the Earth; 
• this Doppler-shift-measured velocity, of various galaxies receding from the Earth, is approximately proportional to their distance from the Earth for galaxies up to a few hundred megaparsecs away. 

This is normally interpreted as a direct, physical observation of the expansion of the spatial volume of the observable universe.

Suomeksi: 

• punasiirtymä voidaan tulkita suhteelliseksi nopeudeksi poispäin maapallosta
• Doppler ilmiöllä mitattu nopeus on suhteessa kohteen etäisyyteen maapallosta tiettyyn etäisyyteen asti

Hubble flow 

The motion of astronomical objects due solely to this expansion is known as the Hubble flow. Hubble's law is considered the first observational basis for the expanding space paradigm and today serves as one of the pieces of evidence most often cited in support of the Big Bang model.

Suomeksi

• Hubblen lakia noudattava liike avaruudessa on Hubblen virtaus. Tämä on ensimmäinen havaittu perusta laajenevan avaruuden paradigmalle ja yleisimmin esitetty todiste Big Bang teorian puolesta.

Hubble constant 

The law is often expressed by the equation v = H₀D, 

• with H₀ the constant of proportionality (the Hubble constant) between the "proper distance" D to a galaxy (which can change over time, unlike the comoving distance) 
• and its velocity v (i.e. the derivative of proper distance with respect to cosmological time coordinate). 

The SI unit of H₀ is s⁻¹ but it is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy 1 megaparsec (3.09×10¹⁹ km) away. 

The reciprocal of H₀ is the Hubble time. 

Suomeksi

• Spektriviivan punasiirtymän tarkan mittaamisen ja Hubblen vakion avulla voidaan määritellä maapallosta poispäin kiitävän galaksin nopeus. 

Hubble time  

• The Hubble constant H₀ has units of inverse time, i.e. H₀ ≈ 2.3×10⁻¹⁸ s⁻¹. 
• "Hubble time" is defined as 1/H₀. 
• The value of Hubble time in the standard cosmological model is 4.35×10¹⁷ s or 13.8 billion years.  

The phrase "expansion timescale" means "Hubble time"

Suomeksi

• "Hubble aika" antaa nykyisten mittausten perusteella tunnetun maailmankaikkeuden iäksi 13.8 miljardia vuotta.

Hubble length 

• The Hubble length or Hubble distance is a unit of distance in cosmology, defined as cH₀^-1 — the speed of light multiplied by the Hubble time. 
• It is equivalent to 4,228 million parsecs or 13.8 billion light years. (The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.) 
• The Hubble distance would be the distance between the Earth and the galaxies which are currently receding from us at the speed of light, as can be seen by substituting D = c/H₀ into the equation for Hubble's law, v = H₀D

Suomeksi

• "Hubblen pituus" on tosi pitkä... Hubblen aika kertaa valonnopeus!
• "Hubblen etäisyys" on maapallon etäisyys niistä galakseista, jotka kiitävät meistä poispäin valonnopeudella.
• Hubblen etäisyys lukeam on sama kuin Hubblen aika, 13.8 miljardia valovuotta

Hubble volume

• The Hubble volume is sometimes defined as a volume of the universe with a comoving size of  cH₀. 

The exact definition varies: it is sometimes defined as the volume of a sphere with radius  cH₀, or alternatively, a cube of side  cH₀. 

Some cosmologists even use the term Hubble volume to refer to the volume of the observable universe, although this has a radius approximately three times larger.

Suomeksi

• Hubblen tilavuus antaa koko maailmankaikkeuden tilavuuden comoving koolla cH₀

Comoving distance

Mitä sitten tarkoittaa "comoving distance"

Pitääkö sitä kaikkea kysyä? 

No, vastaus lähdeviittein ja tarkoin selityksin löytyy tästä wiki artikkelista, jonka johdannon kopsaan tähän vähän värjäten.

In standard cosmology, comoving distance and proper distance are two closely related distance measures used by cosmologists to define distances between objects.

Proper distance roughly corresponds to where a distant object would be at a specific moment of cosmological time, which can change over time due to the expansion of the universe. 

Comoving distance factors out the expansion of the universe, giving a distance that does not change in time due to the expansion of space (though this may change due to other, local factors such as the motion of a galaxy within a cluster). 

Comoving distance and proper distance are defined to be equal at the present time; therefore, the ratio of proper distance to comoving distance now is 1. 

At other times, the scale factor differs from 1. 

The universe's expansion results in the proper distance changing, while the comoving distance is unchanged by this expansion because it is the proper distance divided by that scale factor.

Että hanskassa on laajenevan universumin etäisyydet - joillakin matematiikan ymmärtäjillä ainakin.