This pretty much debunks the young Earth theory.
Distant starlight: 13,700,000,000
The Hubble Deep Field, taken in 1996, showing light that has been in the cosmic vacuum of space for billions of years, not thousands.
See the main article on this topic:
Starlight problem
The fact that distant starlight can be seen from Earth has always been a major problem for the young Earth idea. Because the speed of light is finite, what you are actually seeing when you look at an object is an image of that object
from the past. "From the past" here has a few caveats regarding the
relativity of our concept of the past, the future, and now. In the BBC
Horizon program
What Time Is It? physicist and former pop-synth player
Brian Cox suggested that, as information cannot travel faster than light, and that time and space are relative, it can be considered that the stars actually
are what they look like "now", in a manner of speaking. Either way, though, the bottom line is still the same; the light has travelled a certain distance, for a certain time, before arriving on Earth to be seen by our eyes or telescopes. We can use this data to put a minimum time on the existence of the universe, by looking at how long some light has been travelling for.
On Earth, the delay caused by the speed of light is incredibly minor — when you look at an object a mile away, the light has been travelling for five microseconds. When you look at the Sun, you are seeing light that has been in transit for 8.3 minutes. It's more noticeable with sound and distant objects, but only because the light from things such as distant explosions or jet fighters is so much faster. There's still a delay and transit time for the information that says whatever made the light/sound must have been around that long ago to produce it.
On the cosmic scale of things, this delay is far from minor and really is noticeable. When astronomers look at the closest star to Earth (Alpha Centauri), which is roughly four light years away, they are seeing the star as it was four years ago from our perspective. When astronomers look at objects in the region of space known as the "Hubble ultra deep field", they are seeing the stars there as they were over
ten billion years ago. Light we are receiving from these fields has been travelling for ten billion years, and the universe must have, therefore, existed long enough for that transit time to take place.
The furthest distance away that deep space telescopes can see is somewhere in the region of 13.7 billion years (approximately), this implies that light has taken around 13.7 billion years to travel across the universe to reach us. Thus, one concludes that the universe is at least
13.7 billion years old.
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Therein lies the problem for young Earth creationism; if the universe is only 6,000 years old, how can objects billions of light years away — and therefore billions of years old — be seen?
There are a few creationist "zingers" to solve this problem, but are almost exclusively centred around
pretending the problem doesn't exist. One is omphalism, which suggests the light was already in place and on its way 6,000 years ago, which is basically like saying that "6,000 years ago, the world was created 14 billion years ago", which is a form of
Last Thursdayism. They also like time dilation fields and
changing the speed of light, but this requires a lot of
Goddidit to make it work, as there is zero evidence for why the speed of light should change. There are a lot of issues surrounding changing fundamental physical constants such as
c, namely that according to E==mc2, increasing
c to make the world 6,000 years old would lead to normal radioactive decay blowing the planet up.
Qualified astrophysicist
Jason Lisle came up with the "
anisotropic synchrony convention", which exploits how to reliably measure of the speed of light, but suffers from
special pleading in that it assumes a highly unlikely physical reality deriving from a mathematical quirk is
literally true - and there is
no additional evidence for such a thing.