Question

Galaxies are found in the “walls” of huge voids; very few galaxies are found in the voids themselves. The text says that the structure of filaments and voids has been present in the universe since shortly after the expansion began 13.8 billion years ago. In science, we always have to check to see whether some conclusion is contradicted by any other information we have. In this case, we can ask whether the voids would have filled up with galaxies in roughly 14 billion years. Observations show that in addition to the motion associated with the expansion of the universe, the galaxies in the walls of the voids are moving in random directions at typical speeds of 300 km/s. At least some of them will be moving into the voids. How far into the void will a galaxy move in 14 billion years? Is it a reasonable hypothesis that the voids have existed for 14 billion years?

Answer 1

We note down the given parameters firstly

Total time given = 14 billion years = 14 x 10⁹ years

Speed of the voids = 300 km/s

Since 1 year =365 days

1 day= 24 hours

1 Hour =60 x 60 sec = 3600 sec

Therefore, 24 x 3600 sec = 1 day

86400 sec =1 day

1 year = 365 x 86400 =31536000 sec

Therefore total given time = 14 x 10⁹ x 31536000 sec

= 441504000 x 10⁹ sec

= 441504 x 10¹² sec

The distance the galaxy will travel into the void = 300 km/s x 441504 x 10¹² sec

= 1324512 x 10¹⁴ km

This is the answer to the question.