# ? about speed of light i cant figure out

StopEvangelists
Posts: 51
Joined: 2006-04-14
Offline
? about speed of light i cant figure out

Creationist/6000 year old types claim that since tthe universe was smaller, that the light from distant objects was emitted at a much closer distance to earth, and that light got here now. So even though they are far away, the light we see was actually emitted from a close distance. I know this is BS, just can't figure out why.

I guess that the stars would be moving at such a fast pace that they would all be redshifted...

"Religion is like a badly written contract - most people don't read most (much less all) of it, believe what the other party says, and execute with the best of intentions and naivety."

- Me

Lucretius
Posts: 30
Joined: 2006-04-05
Offline
Re: ? about speed of light i cant figure out

StopEvangelists wrote:
Creationist/6000 year old types claim that since tthe universe was smaller, that the light from distant objects was emitted at a much closer distance to earth, and that light got here now. So even though they are far away, the light we see was actually emitted from a close distance. I know this is BS, just can't figure out why.

I guess that the stars would be moving at such a fast pace that they would all be redshifted...

I haven't heard them claim this before. Usually it's the trash provided by Russell Humphreys. If the view you presented was their view, it's rather easy to demonstrate they are wrong.

Similar to the way that Planck's Constant can be derived by finding the value of a slope comparing frequency of light and the total kinetic energy, something known as the Hubble Constant can be found by finding the value of a line comparing an object's recessional velocity with it's proper distance. The Hubble's Constant provides us with a recessional velocity directly proportional to an objects distance. The further away it is, the faster it recedes.

Now, we can determine the recessional velocity from the redshift using the formula v=zc, where z is the redshift and c is the speed of light. The distance we must find is known as the "proper" distance, the distance the light has traveled in it's rest frame (from a moving perspective this would be thrown off.) We use what are known as "standard candles" to do this, objects like type 1a Supernovae. These objects have a known luminosity, which can be compared with our objects to determine the distance it has traveled.

If we then compare like so: v/D=H, where v is our recessional velocity, and D is our proper distance, we can find hubbles constant H. The problem with the Creationist claim, is that if they demand the universe is as big as it is today, while demanding the universe only be 6,000 years old, the recessional velocity would have to skyrocket because our redshift values would be off, but the distance is the same. This makes H too big. However, our H is rather close to what the value actually is (I say this because there are still debates over the exact value of H, but we aren't as far off as Creationists would need to fit their claim.)

We can see if we can calculate Hubble's Constant, using the Andromeda galaxy as an example. The redshift of this galaxy is 0.00100, so by v=zc we get a recessional velocity of 300,000 m/s, or 300 km/s. The distance from our view is 2.52 million light years. Doing the math, we get a rate of 119 (km/s)/mly or ~91(km/s)/mpc. The currently estimated value is 70(km/s)/mpc ? 2.4 - 3.2, so we weren't too far off (Hubble had originally got a value of 500(km/s)mpc!)

We most likely would not observe any blue shifting in our local cluster with a Hubble's Constant as large as what a 6,000 year old universe would require, because the outward push would most likely overcome the inward pull of gravitational attraction in our Local Group. We would most lkely observe other bizarre events due to relativity, such as the slower aging of objects in relation to us, due to their very fast recessional velocities. With the speed required by Creationists to have Andromeda be where it is in a few thousand years, it would have a much larger redshift, which would increase v greatly, throwing off our Hubble's Constant.

I hope this helped.

StopEvangelists
Posts: 51
Joined: 2006-04-14
Offline
? about speed of light i cant figure out

It did help, but I had to read it twice. That's the problem with science v. creationism for the layperson. The Bible and Creation are all baby talk, and sound good. Reality is just too hard to figure out.

"Religion is like a badly written contract - most people don't read most (much less all) of it, believe what the other party says, and execute with the best of intentions and naivety."

- Me

Lucretius
Posts: 30
Joined: 2006-04-05
Offline
? about speed of light i cant figure out

There is most likely a much simpler way to express the problem. I could simply say that, if we were to have a proper Hubble Constant, everything would have to be redshifted to such a degree that we would expect no blueshift. The expansion of space would have overtaken the local gravitational effects on the Local Cluster.

I wanted to show you why this was, and thus the complex formulae.[/u]