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Question Number 97885 by  M±th+et+s last updated on 10/Jun/20

hello every one how do they calculated the universe old wich is 13.8 billion years

$${hello}\:{every}\:{one} \\ $$$${how}\:{do}\:{they}\:{calculated}\:{the}\:{universe}\:{old} \\ $$$${wich}\:{is}\:\mathrm{13}.\mathrm{8}\:{billion}\:{years} \\ $$

Commented by EmericGent last updated on 10/Jun/20

One way is use the density in function of time and see when the density reach Planck's limit

Commented by  M±th+et+s last updated on 10/Jun/20

thanx for all

$${thanx}\:{for}\:{all}\: \\ $$

Answered by smridha last updated on 10/Jun/20

you can prove this by introducing Hubble constant(H_0 )... but the fact is our universe is expanding, not in constant rate it is accelarating so age of universe cannot determine perfectly ,this is just a theoritical value... well I can prove this...

$$\boldsymbol{{you}}\:\boldsymbol{{can}}\:\boldsymbol{{prove}}\:\boldsymbol{{this}}\:\boldsymbol{{by}}\:\boldsymbol{{introducing}} \\ $$$$\boldsymbol{{Hubble}}\:\boldsymbol{{constant}}\left(\boldsymbol{{H}}_{\mathrm{0}} \right)... \\ $$$$\boldsymbol{{but}}\:\boldsymbol{{the}}\:\boldsymbol{{fact}}\:\boldsymbol{{is}}\:\boldsymbol{{our}}\:\boldsymbol{{universe}}\:\boldsymbol{{is}} \\ $$$$\boldsymbol{{expanding}},\:\boldsymbol{{not}}\:\boldsymbol{{in}}\:\boldsymbol{{constant}}\:\boldsymbol{{rate}} \\ $$$$\boldsymbol{{it}}\:\boldsymbol{{is}}\:\boldsymbol{{accelarating}}\:\boldsymbol{{so}}\:\boldsymbol{{age}} \\ $$$$\boldsymbol{{of}}\:\boldsymbol{{universe}}\:\boldsymbol{{cannot}}\:\boldsymbol{{determine}} \\ $$$$\boldsymbol{{perfectly}}\:,\boldsymbol{{this}}\:\boldsymbol{{is}}\:\boldsymbol{{just}}\:\boldsymbol{{a}}\:\boldsymbol{{theoritical}} \\ $$$$\boldsymbol{{value}}... \\ $$$$\boldsymbol{{well}}\:\boldsymbol{{I}}\:\boldsymbol{{can}}\:\boldsymbol{{prove}}\:\boldsymbol{{this}}... \\ $$

Commented by  M±th+et+s last updated on 10/Jun/20

sir you mean this rule t_0 =(2/3)×(1/(H_0 (√Ω_v_0 )))sinh^(−1) ((√((3Ω_v_0 )/(2(1+q_0 )))) and i hope if you have a time show the prove and thank you.

$${sir}\:{you}\:{mean}\:{this}\:{rule} \\ $$$${t}_{\mathrm{0}} =\frac{\mathrm{2}}{\mathrm{3}}×\frac{\mathrm{1}}{{H}_{\mathrm{0}} \sqrt{\Omega_{{v}_{\mathrm{0}} } }}{sinh}^{−\mathrm{1}} \left(\sqrt{\frac{\mathrm{3}\Omega_{{v}_{\mathrm{0}} } }{\mathrm{2}\left(\mathrm{1}+{q}_{\mathrm{0}} \right.}}\right) \\ $$$${and}\:{i}\:{hope}\:{if}\:{you}\:{have}\:{a}\:{time}\:{show}\:{the} \\ $$$${prove}\:{and}\:{thank}\:{you}. \\ $$

Commented by smridha last updated on 10/Jun/20

its well but you can also determine it in easiest way like.. (1/H_0 )=age of the universe H_0 =((73km/s)/(1Mpc)) it means if the distant bet^n two galaxyies is 1Mpc then the relative velocity of moving away from one to other is 73km/s. so you can see imedeately that distant and velocity is proportional and the proportionality constant is H_0 ..this is called Hubble′s law.

$$\boldsymbol{{its}}\:\boldsymbol{{well}}\:\boldsymbol{{but}}\:\boldsymbol{{you}}\:\boldsymbol{{can}}\:\boldsymbol{{also}}\:\boldsymbol{{determine}} \\ $$$$\boldsymbol{{it}}\:\boldsymbol{{in}}\:\boldsymbol{{easiest}}\:\boldsymbol{{way}}\:\boldsymbol{{like}}.. \\ $$$$\frac{\mathrm{1}}{\boldsymbol{{H}}_{\mathrm{0}} }=\boldsymbol{{age}}\:\boldsymbol{{of}}\:\boldsymbol{{the}}\:\boldsymbol{{universe}} \\ $$$${H}_{\mathrm{0}} =\frac{\mathrm{73}\boldsymbol{{km}}/\boldsymbol{{s}}}{\mathrm{1}\boldsymbol{{Mpc}}}\:\boldsymbol{{it}}\:\boldsymbol{{means}}\:\boldsymbol{{if}}\:\boldsymbol{{the}} \\ $$$$\boldsymbol{{distant}}\:\boldsymbol{{bet}}^{\boldsymbol{{n}}} \:\boldsymbol{{two}}\:\boldsymbol{{galaxyies}}\:\boldsymbol{{is}} \\ $$$$\mathrm{1}\boldsymbol{{Mpc}}\:\boldsymbol{{then}}\:\boldsymbol{{the}}\:\boldsymbol{{relative}}\:\boldsymbol{{velocity}} \\ $$$$\boldsymbol{{of}}\:\boldsymbol{{moving}}\:\boldsymbol{{away}}\:\boldsymbol{{from}}\:\boldsymbol{{one}}\:\boldsymbol{{to}}\:\boldsymbol{{other}} \\ $$$$\boldsymbol{{is}}\:\mathrm{73}\boldsymbol{{km}}/\boldsymbol{{s}}. \\ $$$$\boldsymbol{{so}}\:\boldsymbol{{you}}\:\boldsymbol{{can}}\:\boldsymbol{{see}}\:\boldsymbol{{imedeately}}\:\boldsymbol{{that}} \\ $$$$\boldsymbol{{distant}}\:\boldsymbol{{and}}\:\boldsymbol{{velocity}}\:\boldsymbol{{is}}\:\boldsymbol{{proportional}} \\ $$$$\boldsymbol{{and}}\:\boldsymbol{{the}}\:\boldsymbol{{proportionality}}\:\boldsymbol{{constant}} \\ $$$$\boldsymbol{{is}}\:\boldsymbol{{H}}_{\mathrm{0}} ..\boldsymbol{{this}}\:\boldsymbol{{is}}\:\boldsymbol{{called}}\:\boldsymbol{{H}}{ubble}'\boldsymbol{{s}}\:\boldsymbol{{law}}. \\ $$

Commented by smridha last updated on 10/Jun/20

thank you...

$${th}\boldsymbol{{ank}}\:\boldsymbol{{you}}... \\ $$

Commented by  M±th+et+s last updated on 10/Jun/20

god bless you sir

$${god}\:{bless}\:{you}\:{sir} \\ $$

Answered by Rio Michael last updated on 10/Jun/20

The truth is that we cannot actually determine the actual age of the universe due to its expanding nature. Astronomers tell us that the universe is about 13.7 to 13.8 billion years. They do calculations − Based on the oldest star(methusela star). − by measuring the rate at which the universe is expanding from the big bang start point.

$$\mathrm{The}\:\mathrm{truth}\:\mathrm{is}\:\mathrm{that}\:\mathrm{we}\:\mathrm{cannot}\:\mathrm{actually}\:\mathrm{determine} \\ $$$$\mathrm{the}\:\mathrm{actual}\:\mathrm{age}\:\mathrm{of}\:\mathrm{the}\:\mathrm{universe}\:\mathrm{due}\:\mathrm{to}\:\mathrm{its}\:\mathrm{expanding} \\ $$$$\mathrm{nature}.\:\mathrm{Astronomers}\:\mathrm{tell}\:\mathrm{us}\:\mathrm{that}\:\mathrm{the}\:\mathrm{universe}\:\mathrm{is} \\ $$$$\mathrm{about}\:\mathrm{13}.\mathrm{7}\:\mathrm{to}\:\mathrm{13}.\mathrm{8}\:\mathrm{billion}\:\mathrm{years}.\:\mathrm{They}\:\mathrm{do}\:\mathrm{calculations} \\ $$$$−\:\mathrm{Based}\:\mathrm{on}\:\mathrm{the}\:\mathrm{oldest}\:\mathrm{star}\left(\mathrm{methusela}\:\mathrm{star}\right). \\ $$$$−\:\mathrm{by}\:\mathrm{measuring}\:\mathrm{the}\:\mathrm{rate}\:\mathrm{at}\:\mathrm{which}\:\mathrm{the}\:\mathrm{universe}\:\mathrm{is}\: \\ $$$$\mathrm{expanding}\:\mathrm{from}\:\mathrm{the}\:\mathrm{big}\:\mathrm{bang}\:\mathrm{start}\:\mathrm{point}.\: \\ $$

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