Cosmology

by Chris Lawton

Cosmology is the study of the universe and in particular where it came from. In the other Astronomy pages I have sought to indicate objects of interest and relevance. Cosmology is, however, different. It involves stars, galaxies and beyond. Within this broad topic I will do my best to make a very complicated subject a little more understandable.

Get The Picture

The earth is eight light minutes from the sun. That is to say that light leaving the sun now will reach us in eight minutes time. The next nearest star, proxima Centauri, is 4.19 light years (ly) away from us. One light year is 9.5 x 10¹² km. The Milky Way, our galaxy, is approximately 100 000 ly in diameter. The nearest large scale galaxy to us is Andromeda at 2.2 million ly. I could go on, but basically most objects are a long way from us ! All these vast distances raise the question of where did it all come from. All that we understand about the universe as astronomers comes from the answer to this question, as its implications are vast.

One Big Bang ?

The Big Bang theory basically suggests that all matter was created in a single explosion at some point in time. Out of that explosion came everything within the universe. Because it exploded from an infinitesimally small point the universe must, therefore, be expanding. Thermodynamics states that anything that is expanding must radiate heat and hence must cool if no energy is put in. In 1948 Gamow and his research team calculated that this temperature would now be no more than -268 °C !

By 1964 it had been measured, chiefly by Penzias and Wilson, who found the temperature to be -270 °C. The problem in obtaining a more accurate measure was due to atmospheric absorption and a satellite would be needed to make the observations. COBE - The COsmic Background Explorer - was built with the aim of mapping the cosmic background radiation. In 1990 it produced its first results, showing that the temperature of the radiation was - 270.265 °C and smooth to one part in 10 000.

This result provided confirmation, but one quest still remained. The background, if totally smooth, would not allow formation of galaxies. The proposal was, however, that very small ripples in the background on the scale of one part in 100 000 would be enough to cause galaxies to form. In 1992 a second set of COBE results were published showing this to be the case. Astronomers had found their evidence for the Big Bang. They didn't know how or when but they generally believed that this was the way it had happened.

Cosmological Principle

This is a reduction that is applied to the universe in an effort to make it more understandable. It requires the universe to be homogeneous and isotropic in all places but not at all times. Any observer in any place, but not time, must see the same, i.e. spatial uniformity exists, temporal doesn't. This principle means we can look at our part of the universe and extrapolate from it to the rest of the universe.

Hubble's Law

Hubble's Law was built around the concept of Einstein's theory of relativity. There are two key points for us in relativity - no absolute reference system exists and the velocity of light is invariant. Einstein also postulated that, like shrapnel from an explosion, the pieces of the Big Bang must all be accelerating away from the center.

In 1929, from measurements of over 40 galaxies, Edwin Hubble demonstrated that galaxies did move away from us. Further he showed that the velocity of recession was proportional to how far away the galaxy is. This became known as Hubble's Law, i.e. V=H_oD where H_o is the Hubble constant.

The value of this constant is much debated and is critical to our estimates of the age of the universe, for the inverse of H_o is the age of the universe. Current values for H_o vary by a factor of two. I should also point out that the Hubble constant isn't constant and varies very slowly over time.

Determining H_o

To estimate H_o we have to find some other way of measuring the distance to our galaxy that does not require a measurement of V and therefore Hubble's Law. This done by using standard candles. These are taken to be objects whose properties are well known and so variations in output are due solely to their distance away. For objects up to 50 kpc we can use stars. After this we use Cepheid variable stars. These stars vary in brightness in such a manner that their period of oscillation is related to the luminosity. By calibrating to nearby Cepheids, a measure of distance can be obtained. This takes us to 4 Mpc. After this a host of the brightest objects in the galaxies are used to make a distance measure. (Sorry for the use of another unit but 1 pc or parsec = 3.086 x 10¹³ km). Current values for H_o range from 50 to 100 km s^-1 Mpc^-1.

It is debatable but more hours of research are probably spent in finding out this value than anything else in astronomy right now. The problem is made worse in that the higher this value is, the younger the age of the universe. Unfortunately some of the ages being calculated are too short to allow for stellar evolution as we understand it.

The End?

If the beginning is in the Big Bang, what about the end ? Again astronomers are uncertain of this. It all depends on the amount of mass in the universe. If this value, omega_o, is greater than 1 then the universe will collapse in a big crunch, less than 1 and it will expand forever, and if it is equal to one it will take forever to just stop expanding and never contract.

You may find it surprising, but omega_o is related to H_o. This makes accurate determination of this value even harder to achieve. One problem we have right now is that of missing mass within the universe. Most astronomers call this dark matter, and the quest for it is almost as energetic as that for H_o.

Summary

Basically astronomers know the universe probably started in a single explosion around 10 billion years ago. How and when it will end is uncertain, but the omega_o=1 option is the most pleasing, even if it is not the most likely.

In reality the whole process of cosmology and the theories behind the Big Bang are far more complex than I have explained here. Hopefully I have given you a flavour of the challenges facing cosmologists.

God

As a Christian I must ask, where does God fit into all this? Should the early chapters of Genesis be taken literally? The Bible devotes very little time to creation, but perhaps that is because the Bible is concerned about people's relationship with God not where they come from. Cosmology does not, in my opinion, exclude God. God created the universe ex nihilo (out of nothing) and the Big Bang does not exclude this as an option.

I will now attempt to outline a Christian, biblically based perspective of creation, and try and see how this fits in with the scientific theories outlined above. I am very grateful to Tony Watkins for allowing me to use his notes on this subject as a guide.

Why, therefore, do science and the Bible seem to so openly conflict? There are generally considered to be two answers to this. The first response to the conflict is to look at the question being asked. Science seeks to answer how the universe came about. It has a mechanistic perspective - how do things operate in the universe? How does it work? The Bible asks why was the world created. It is about significance and therefore has a theological perspective.

The second response is based around the provisional nature of our knowledge and understanding. Scientific theories are never complete and final; they are always open to disproof. For 400 years the theories of Sir Isaac Newton were deemed to be correct. To a large extent in our everyday life they are correct. However, the theories of Albert Einstein are much more accurate and do not fall down under extreme conditions.

Likewise biblical interpretation is flawed. The Bible itself is true and trustworthy, but our understanding of it is open to our own personal interpretation of a given passage.

The conflict between science and religion centres around Genesis 1. We have, however, missed the point in mistakenly making Genesis answer questions of science. It can, however, answer questions of metaphysics and significance. There are five ways of approaching Genesis 1 and I will now look at each of these approaches.

Literal Approach

The first way we can look at the early part of Genesis is to say that God created the earth in six days of 24 hours, the earth is around 10 000 years old and the fossil record is due to the flood.

Gap Theory

Between Genesis 1 v1 and Genesis 2 v2 a gap of an indeterminate amount of time can be introduced. There is no reason why the passage should immediately follow. Such an approach can be said to be unsatisfactory for it is manipulating scripture to reconcile the Bible with science.

Days?

The Hebrew word used for day in Genesis can in fact mean a period of time - an epoch rather than a literal period of 24 hours. This principle is borne out in 2 Peter 3 v8 which says: "With the Lord a day is like a thousand years, and a thousand years are like a day."

A Revelation?

The six days merely represent a revealing by God of how he created the universe. This idea is very plausible and doesn't violate the value of scripture.

Literary-Cultural Approach

This aspect needs expanding more than the others but essentially revolves around looking at Genesis 1 in the same way we would attempt to understand the rest of scripture.

We firstly need to look at the genre of Genesis 1. Is it prose or is it poetry? It is clearly not a historical narrative. Secondly, the purpose of Genesis 1-11 seems to be a theological tract against the false religious ideas of the Ancient Near East. Thirdly, we have the structure of Genesis; it sets the scene for the whole Bible in that it introduces us to the people of God (Israel) through whom God would fulfill his promises.

Purpose of Genesis 1-11

The writer(s) of Genesis were probably aware of several current creation accounts in the Ancient Near East. Genesis 1 v1 to Genesis 2 v3 is a repudiation of such myths. There are five areas of attack:

God creates sea monsters; in other religions they are rivals whom the gods defeat.
In the myths the gods struggle to separate the lower and upper waters, whereas in Genesis God separates them.
Worshiping of the sun, moon and stars was common, particularly amongst the Babylonians, but in Genesis we see that they are just lights and are not meant for worship.
The fourth area of attack is based on the value of mankind. Many underlying beliefs had humans created as an afterthought to relieve the gods of work and to provide food for them. The Bible shows that humans are worth far more than this and are the pinnacle of God's creation.
Finally the means of creation in Genesis is by God's spoken word. Egyptian belief suggested that the gods created through magic.

In all these we see that the Bible and its teaching were clearly against the beliefs of the surrounding areas. When viewed in this context we can see that Genesis and science are answering completely different questions. What, therefore, do we learn from the Bible about creation?

Firstly, we see a creator God who is outside the time frame of the universe. Secondly, God is supreme and is without equals or competitors. Thirdly, God is more than just a creator; he provides laws as well. Finally, we live in a world reflecting its creator and in which we clearly know our role.

All this sounds very different from the first half of this paper. There is no mention of an explosive creation, the ripples of which we can still detect today. But then science offers no explanation as to why we have a sense of right or wrong. Clearly when looking at origins it is good to look at all available sources, but in so doing we must look at each of them in the right context.

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