Tuesday, May 7, 2013

The Effects of Gravitational Time Dilation and Universal Expansion on Distant Starlight

We’ve all heard the estimates about the distances light travels from certain stars and they’re literally astronomical. Based on the travel time of the light from these stars they are estimated at billions, even trillions of light years away. I have no doubt that the distances are being correctly calculated, but because time is relative, there isn’t the direct correlation to age that most people seem to believe

Gravitational Time Dilation
A Black Hole
If you’ve watched any science fiction you’ve likely become familiar with this concept. The idea supported by general relativity is simply that actual time moves slower the closer you are to a gravitational mass. This can be tested by setting two clocks to the exact same time and then moving one to a very high altitude (further from a gravitational mass) and one to a very low altitude (closer to a gravitational mass). Leave them there for a while and then compare the times. They will be off by just a little bit. This same phenomenon can be created using acceleration (which generates gravitational force or g-force). Naturally the effect on Earth is minimal, but the stronger the gravitational influence, the more pronounced the effect will be. This is often demonstrated with the example of a black hole where the gravity is so intense that not even light is fast enough to escape the fall of space into the gravitational mass and time itself comes to a complete standstill. This is of course an extreme case and naturally the effect is far less pronounced with other masses, but still present.

Now when we think about light traveling from one place to another, we often forget to factor in the effects of gravitational time dilation. Light traveling from our sun takes about 8 minutes to get from there to here, from our point of reference. However, given its acceleration and the fact that it’s traveling through a massive gravity well (the sun) to get to us, the actual elapsed time for the photon in question would be significantly less. As the acceleration factor only alters the time experienced for the photon itself and not so much travel time, we’ll set aside that consideration for now, but think about distant starlight. As it leaves its star it leaves a rather large gravity well (the star). As it continues to travel, time elapsing much faster outside the star’s gravity, it continues to leave the effect of other gravity wells (the solar system, the local system cluster, and ultimately the galaxy and the super-massive black hole sitting at its core) until it is traveling in open space. Without the effect of gravity time elapses very quickly in these areas with potentially millions and even billions of years passing in what seems like a couple thousand for us here on Earth in our own fairly significant gravity well. This means that the star that’s a couple billion light years away actually gets its light to us within a couple thousand years from our perspective

The implication of this of course is that the age of the universe may well be several billion or even trillion years old, without necessitating that the Earth be more than perhaps 10,000 years old.

Universal Expansion
The Milky Way Galaxy
While it’s true the theme park is always expanding, I’m actually referring to the universe itself. Since the event that spawned the whole of the physical world, referred to as the Big Bang, the universe has been and is continuing to expand, growing ever larger each moment. This effect can be seen by observing distant stars. Any object that produces light can be analyzed to determine if it’s approaching, remaining a consistent distance away, or moving away from the observer. This is done by examining the light waves coming from the object and seeing if they’re being compressed into less space (shifting the light to the blue end of the visible light spectrum) or being stretched out over more space (shifting the light to the red end of the visible light spectrum). A blue shift indicates the object is approaching, whereas a red shift indicates that it’s moving away. With the exception of a few bodies that are close enough to our galaxy to be affected by its gravity enough to be approaching (other galaxies in our local group) everything in the universe can be seen to be moving away from us, indicating that the universe is still expanding.

What this means for distant starlight is that the original distance it needed to travel to get here is actually less than what it is now. In fact it was significantly less a second ago than what it needs to travel now. This means that while those stars that are several billion light years away now are indeed that far away, when they were first born and when we first received light from them, they may not have been nearly that far away meaning that a star’s distance now, is not an accurate measure of the age of the universe.

Combining these two factors together presents interesting new options for theorists on the age of the universe and what that might mean for humanity. Most notably proponents of a young earth will stand to gain the most from these potential new theories giving greater credence to their ideas and beliefs. If you find these ideas intriguing, be sure to share this article with your friends, as I’d love to see some of the spin off theories show up in another N3rd C0rn3r.