The Age Of The Universe: Then Vs. Now From Early Estimates To Modern Discoveries
Before The 2000s, Astronomers Estimated That The Age Of The Universe Was Between 7 And 21 Billion Years.
But As Our Technology Advanced And New Techniques Were Developed, We Discovered That The Exact Age Of The Universe Is 13.7 Billion Years, With An Uncertainty Of Only 200 Million Years. How Is This Possible?
Early Estimates: How Scientists First Calculated The Age Of The Universe
In The 1920s, Edwin Hubble Made A Very Important Discovery — He Observed That The Universe Is Expanding. He Noticed That The Farther Away Galaxies Are, The Faster They Are Moving Away From Us. This Observation Led To A Simple Law: V = Ho × D, Where V Is The Speed Of The Galaxy (In Km/S), D Is Its Distance (In Megaparsecs), And Ho Is The Hubble Constant.
When We Can Accurately Measure The Speed And Distance Of Individual Galaxies, We Can Find The Value Of The Hubble Constant. Astronomers Also Discovered That The Estimation Of The Age Of The Universe Is Directly Linked To The Hubble Constant — Usually It Is Between 1/2 To 2/3 Of A Century, Depending On Which Cosmological Model We Are Using.
The Speed Of Galaxies Is Known By Their Redshift — Basically By Observing Changes In Their Spectrum. But To Measure Distance, Scientists Use A Special Type Of Pulsating Stars Called Cepheid Variables. The Actual Brightness Of These Stars Is Related To The Period When Their Brightness “Blinks” — The Time They Are Bright And Dim, That Is How Far Their Distance Can Be Estimated.
But The Problem Was That Ground-Based Telescopes Could Not See Faint Objects Clearly. Therefore Distance Measurements Were Not Accurate. Until The 1990s, Estimates Of The Hubble Constant Were In A Fairly Wide Range – Between 50 And 90 Km/S/Mpc. Therefore Estimates Of The Age Of The Universe Were Also Broad: From 7 Billion To 21 Billion Years.
Revolutionizing Astronomy: The Role Of The Hubble Space Telescope
In 1993, The Hubble Space Telescope Started An Important “Key Project” Aimed At Accurately Measuring The Distances To Cepheid Stars Within 18 Galaxies. For The First Time, Astronomers Were Able To Measure Such Precise Distances And Finally Found An Accurate Value For The Hubble Constant (Ho).
By 1999, After Several Years Of Hubble Telescope Observations, Scientists Estimated Ho To Be About 71 Km/S/Mpc, With Only 10% Uncertainty — A Major Breakthrough For Modern Astronomy. When This Value Was Traced Back To The Big Bang, The Age Of The Universe Was Estimated To Be Between 9 And 14 Billion Years.
This image is of galaxy NGC 4603, which was captured by the Hubble Space Telescope in 1996 and 1997. Astronomers used about 50 Cepheid variable stars in this galaxy to calculate that this galaxy is 108 million light years away from us. This was the farthest galaxy at that time and was used to determine the value of the Hubble Constant in an important project of HST.
(Image credit: Jeffrey Newman – UC Berkeley, and NASA)
Wmap And The Big Bang: A New Way To Measure The Universe's Age
In February 2003, The Wmap Project Released A Detailed Map Of The Entire Sky, Showing The Radiation Emitted At A Time When Not A Single Star Had Yet Formed.
This Radiation Is What We Call The Cosmic Microwave Background (Cmb) — It’s Basically The Heat Left Over From The Big Bang. The Idea Was First Proposed By George Gamow And Robert Dicke In 1946.
Since Then, Scientists Have Been Trying To Detect And Analyze The Cmb. The Cmb Was First Accidentally Detected In 1965, When Arno Penzias And Robert Wilson Were Using A Radiometer — A Tool That Detects Radio Signals.
He Noticed A Strange Extra Signal In His Device, Which Was Coming From Everywhere. Later He Understood That This Is The Same Cmb – A Thermal Radiation Which Is Present Everywhere In The Universe At A Temperature Of 2.725 Kelvin.
Then In 1992 A Satellite Came – Cobe (Cosmic Background Explorer). It Made A Map Of Cmb For The First Time And Told That There Are Some Big Fluctuations In Cmb. Scientists Considered These Fluctuations As Proof Of The Formation Of Galaxies And The Empty Space (Voids) Between Them.
But The Real Breakthrough Came From The Wmap Satellite, Because Wmap Was So Sensitive That It Could Detect Even The Smallest Details. Because Of This, Scientists Were Able To Calculate The Exact Age Of The Universe.
The Wmap Team Created A Model That Perfectly Fits Their Data. According To That Model:
70% Of The Energy In The Universe Is In The Form Of Dark Energy,
26% Is Cold Dark Matter,
And Only 4% Of The Matter Is That Which Is Made Of Atoms And Photons – That Is, What We Can See.
According To Their Calculations, The Age Of The Universe Is About 13.7 Billion Years, And It Has An Uncertainty Factor Of 200 Million Years. The Hubble Constant (Ho) Value Given By Wmap — 71 ± 4 Km/S/Mpc — Also Matches The Results Of The Hst Key Project.
Astronomers compare WMAP data with different models to understand the properties of the universe. They adjust values in the models — such as when the first stars formed, how much dark matter there is, the age of the universe, etc. — until their model matches WMAP’s observations. The model that best matches the data gives the universe as an age of 13.7 ± 0.2 billion years.
Alternative Methods: Star Dating And Other Scientific Approaches
Another Interesting Way To Find Out The Age Of The Universe Is To Calculate The Age Of The Oldest Stars In It. These Old Stars Are Usually Located Within Globular Clusters, And Scientists Have Estimated Their Age In Great Detail In The Past Few Years.
But There Was A Time When Astronomers Got A Little Confused. They Thought That These Stars Were A Few Billion Years Older Than The Universe Itself – While The Age Of The Universe Was Coming Out Of The Hubble Constant And Coming Out To Be Something Else. So Then The Question Arises: Is The Mistake In The Hubble Constant Or In The Age Estimate Of The Stars?
Later I Realized That Estimating The Age Of Stars In Globular Clusters Is Not That Simple. There Are Many Complications In This – Like The Exact Distance To The Clusters Must Be Known, And There Are Also Some Limitations In The Models Of Stellar Evolution. All These Things Made The Earlier Estimates Inaccurate.
The Age Of Globular Clusters Actually Depends On The Brightness Of Rr Lyra Stars – The Lower Their Luminosity, The Greater Their Distance. And This Distance Helps Us To Tell The Age Of The Clusters. Accurate Distance Measurements Became Possible Only When The European Hipparcos Satellite Was Launched In The Mid-90s.
When The Distance Was Re-Measured Based On The New Data, The Estimated Age Of The Clusters Dropped From 15 Billion Years To Approx. 11.5 Billion Years — With Just About 1 Billion Year Of Uncertainty. Now These Numbers Match Perfectly With The Hubble Constant And The Wmap Data.