Cosmic age problem

<p>The cosmic age problem was a historical problem in astronomy concerning the <a href="/facts/Age_of_the_universe/BaByputq">age of the universe</a>. The problem was that at various times in the 20th century, the universe was estimated to be younger than the oldest observed stars. Estimates of the universe's age came from measurements of the current expansion rate of the universe, the <a href="/facts/Hubble_constant/FJYfELCP">Hubble constant</a> 
  
    
      
        
          H
          
            0
          
        
      
    
    {\displaystyle H_{0}}
  
, as well as cosmological models relating 
  
    
      
        
          H
          
            0
          
        
      
    
    {\displaystyle H_{0}}
  
 to the universe's matter and energy contents (see the <a href="/facts/Friedmann_equations/B9s5rjB9">Friedmann equations</a>). Issues with measuring 
  
    
      
        
          H
          
            0
          
        
      
    
    {\displaystyle H_{0}}
  
 as well as not knowing about the existence of <a href="/facts/Dark_energy/6bWIYewA">dark energy</a> led to spurious estimates of the age. Additionally, objects such as galaxies, stars, and planets could not have existed in the extreme temperatures and densities shortly after the <a href="/facts/Big_Bang/I5T1vTnv">Big Bang</a>.
</p><p>Since around 1997–2003, the problem is believed to have been solved by most cosmologists: modern cosmological measurements lead to a precise estimate of the age of the universe (i.e. time since the Big Bang) of 13.8 billion years, and recent age estimates for the oldest objects are either younger than this, or consistent allowing for measurement uncertainties.
</p>

Cosmic age problem open-in-new

Cosmic age problem