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The universe is about 13.8 billion years old, yet the observable universe, the part whose light has had time to reach us, is about 93 billion light-years across. The difference comes from the expansion of space while that light was travelling.

Cosmology

Science

The story behind the card

A light-year is the distance light travels in a year, about 9.5 trillion kilometres. The oldest light we can detect, the cosmic microwave background, set off about 380,000 years after the Big Bang. During its 13.8-billion-year journey, space kept stretching, so the matter that sent it is now about 46 billion light-years away in every direction, which gives a diameter of about 93 billion. This does not break the rule that nothing travels faster than light: galaxies are not racing through space; the space between them is growing. The expansion was discovered in the 1920s by Georges Lemaître and Edwin Hubble. How big the whole universe is remains unknown; it may even be infinite.

Türkçe oku
Evren yaklaşık 13,8 milyar yaşında, ama gözlemlenebilir evrenin çapı yaklaşık 93 milyar ışık yılı. Gözlemlenebilir evren, ışığının bize ulaşmaya vakit bulduğu bölümdür. Aradaki fark, ışık yoldayken uzayın genişlemeyi sürdürmesinden gelir.

Işık yılı, ışığın bir yılda aldığı yoldur; yaklaşık 9,5 trilyon kilometre eder. Algılayabildiğimiz en eski ışık olan kozmik mikrodalga arka plan ışıması, Büyük Patlama'dan yaklaşık 380.000 yıl sonra yola çıktı. 13,8 milyar yıllık yolculuğu boyunca uzay genişlemeyi sürdürdü; bu yüzden o ışığı yayan madde bugün her yönde yaklaşık 46 milyar ışık yılı uzaktadır. Bu da yaklaşık 93 milyar ışık yıllık bir çap eder. Bu durum, hiçbir şeyin ışıktan hızlı gidemeyeceği kuralını çiğnemez: Galaksiler uzayın içinde son hızla uzaklaşmıyor; büyüyen, aralarındaki uzayın kendisi. Evrenin genişlediğini 1920'lerde Georges Lemaître ve Edwin Hubble ortaya koydu. Evrenin tamamının ne kadar büyük olduğu ise bilinmiyor; sonsuz bile olabilir.

Sources and further reading

Background reading: Observable universe
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