How Big is the Universe?
Why Should A Christian Care About the Size of the Universe?
One of the interesting arguments for a great age of the earth is the size of the universe. The argument goes like this:
*One popular estimate at the time of this writing.
If you read our Creation Versus Evolution page, or our Dinosaurs and the Bible page you know that we stated that the earth is less than 10,000 years old. If the universe was formed 13 billion years ago as a result of a big bang (or some other mechanism), this young age of 10,000 years does not seem reasonable. However, a straightforward reading of the creation account in Genesis does not allow for the universe (and our world) to evolve over billions of years. Since the predicted ages from these two sources are in conflict, most people (unfortunately) take one of two positions:
The fact is that neither of these viewpoints is accurate. The Bible and science are not in conflict, a fact we establish on our Science and the Bible page.
Therefore, you ask, How can you explain having a 10,000 year old Earth if science and the Bible agree? The universe has been proven to be 13 billion years old hasnt it? We are glad you asked. (You did ask, didnt you? )
Note: Except for parts of the Milky Way, most of the stars visible to the naked eye are closer than 6,000 light years. Therefore, this page deals primarily with stars and galaxies that can be seen and measured only with the help of scientific equipment.
How Astronomers Measure the Distances
To understand where the numbers come from, you need to understand how the size of the universe is measured. We located an excellent (and completely unbiased) source on the Internet that explains how science measures these distances and will include the links for you as the reasoning progresses below.
The First Measurement Technique, the Parallax Method
Stated simply, as the Earth orbits the Sun, our viewpoint of the universe changes. Astronomers observe the apparent change in position that closer stars make relative to distant reference stars while the Earth moves. Less apparent movement implies that the star being measured is farther away (and behaving more like the reference stars). More movement implies that the star being measured is closer to the earth (and behaving less like the reference stars). The best measurements are made 6 months apart, since those are the two points at which our viewpoint from the Earth has changed the most (half an orbit). This measurement technique makes the assumption (not specifically stated) that the reference stars do not move or move in a pattern we know perfectly. For a brief explanation of the parallax method, click on the link below.Determining Distances Through Parallax
Lets see how this method works with the star closest to the Earth, Alpha Centauri. (Note: the results on this page are rounded to the nearest three significant digits.)
The formula looks like this:
Therefore, if d = 4.28 light years, then p = 0.762 arc seconds. Now lets look at the facts:
Now, lets repeat the calculations, for an object that is 10,000 light years from usthe greatest distance we would expect from reading the Bible.
If d = 10,000 light years, then p = 0.000326 arc secondsonly 0.0000000906 degrees.
Summing up again, we now add the following difficulty (to those encountered in the measurements made to Alpha Centauri).
Is it possible that this bending of light (alone) could reach a level of 90 billionths of one degree? (The size of the measurement.) The conclusion is obvious. The parallax measurement, even for an object only 10,000 light years away (and therefore still in our Galaxy, the Milky Way), is so tiny that it is very difficult to measure accurately. This implies that the parallax method is not really valid for determining the distance of anything that is farther away than approximately 10,000 light years.
The Second Measurement Technique, the Luminosity Method
Astronomers are aware of the parallax methods shortcoming and have other ways of measuring larger stellar distances. Unfortunately, all of these other techniques measure distances indirectly. For example, we can calculate the distance to a star once we know its luminosity, or energy output. (Luminosity is not the same as the stars apparent brightness, although the two values are connected.) For a brief explanation of the luminosity method, click on the link below.
If you used the link, you noticed that the luminosity method depends on the accuracy of the parallax method to establish standards. Stated another way, a stars luminosity can be calculated with certainty only if we already know the distance to the star.
The Ultimate Measurement Technique, Using Cepheid Variable Stars
Cepheid variable stars are stars whose apparent brightness change with time. In 1912 Miss Henrietta Leavitt reported the period-luminosity relation of Cepheid variable stars in the Small Magellanic Cloud (currently considered to be the third closest galaxy to ours). Stated simply, when the length of the variable stars period (the duration between the stars times of highest brightness) is plotted on a logarithmic chart against its (estimated) luminosity, the result is a straight line. This implies that if you measure the stars period, you can use the graph to estimate its luminosity. Today, the use of Cepheid variable stars is considered the most reliable method available for measuring large cosmic distances. To find out more about this technique, click on the link below.
Notice that even these special stars need to be measured (calibrated) by some other method to define their actual luminosity. Although we are in no way criticizing the work that has been done in astronomy, it should be apparent that for distances beyond a few thousand light years that the distances are still estimates. To demonstrate this point, lets examine the parallax measurement required to fix the distance to a Cepheid variable star in the Small Magellanic Cloud.
Astronomers currently estimate the Small Magellanic Cloud to be about 210,000 light years from Earth. Therefore, using our parallax formula, we know that if d = 210,000 light years, then p = 0.0000155 arc seconds, or 0.00000000431 degrees. Based on this, we know that when the scientists first measured the distance to this star, they measured a parallax of 0.0000155 arc seconds. This parallax measurement precisely confirmed the distance and standardized the period/luminosity graph, allowing astronomers to use it with confidence.
What About VLBA?
You may read about the use of the VLBA, the Very Long Baseline Array string of ten radio telescopes stretching from Mauna Kea Hawaii to St. Croix Virgin Islands (about 5,000 miles). It is reported that by using the VLBA that accurate distance measurements can be made to NGC4258 (reported to be 23.5 million light years away). Coordinating these ten radio stations to work together as the worlds largest dedicated, full-time astronomical instrument is impressive. Still, a claim that the VLBA can accurately define the distance to an object over 20 million light years away may be deceptive.
The VLBA is primarily a telescope designed to produce images of celestial bodies. It is not a distance measuring device. (Note: these images are patterns of radio waves which are like, but not the same as, visible light images seen through a conventional telescope.) The VLBA can very accurately observe a variety of radio phenomena in the frequency 100 MHz to 100 GHz and display them in great detail. (The detail, or resolution, of those images can be as fine as one thousandth of an arc second. This resolution is like measuring the print quality of a laser printer in dots per inch.) Still, although such signals give us a good, sharp picture, they do not indicate distance. Stated another way, the VLBA must use techniques like those we discussed on this page to measure distances, and an attempt to refer to its technology as a way of directly measuring these great distances is deceptive. Incidentally, this is not meant in any way to diminish the value of the efforts of the people associated with the VLBA, or research done by the National Radio Astronomy Observatory. (At our site, we have shown repeatedly that science is good.) It is only intended to show that the primary purpose of the VLBA is not distance measurement.
The Final Analysis
Now, look at what you just read. We understand that science can make some amazing measurements. Still, how valid is an angular measurement that requires the following?
What happens if any of the stars moved and/or the light was bent one ten millionth of a degree when the parallax measurement was being made? Under such conditions, we could be led to believe that a star 10,000 light years away was actually 210,000 light years away. (Remember, we are still looking at distances of only 210,000 light years, not 13,000,000,000 light years.) For that matter, what happens if your reference stars were not as far away as you thought they were?
Although science has great faith in the measurement of the brightness of variable stars, the connection of that brightness to their actual luminosity and their distance is weak (since they are indirect measurement methods). If you followed our comments, you should realize that believing in stellar measurements of more than a few thousand light years requires more faith than believing the Bible. To be fair, the lack of more accurate stellar measurement techniques does not prove that our universe extends only 10,000 light years either. The choice of which numbers you choose to believe is yours.
One More WrinkleTime
According to the theory of relativity, time changes for anything that moves at high speed (that is, anything that has high velocity). This is especially true when that velocity approaches the speed of light. For example, the theory tells us that if some people made a round trip to the Andromeda Galaxy in a space vehicle that traveled at the speed of light, they would think the round trip took them about thirty years. However, here on Earth that crew would not seem to return until 4 million years later.
Now, consider that we live in an expanding universe that scientists tell us is the result of an explosion. If the big bang theory is true,* the Earth and all the other heavenly bodies are moving at explosive but unknown velocities. Would you agree that this makes time calculations rather difficult? (Remember, this time is used with the Cepheid Variable Star data to estimate the age of the universe.)
As you can see, one problem leads to another, leaving us with more unanswered questions than we had before. Since time itself varies by huge factors when the observers frame of reference changes, how can scientists identify the frame of reference that measures the age of the universe? The truthful answer is they can not.
On the other hand, the Bible has proven itself to be true and accuratesomething we briefly demonstrate on our How Do You Know The Bible Is True? page. Since both the size and the age of our universe are difficult to define, and since the Bible is a document that has proven itself true for over 1,900 years, you may then agree with us that it makes more sense to accept what the Bible says at face value. (That is, you can trust the Bible when it tells you that you can literally go to heaventhe real bottom line for all of us.)
Copyright © 1998, 1999 by Clarifying Christianity (SM).
All Bible passages were taken from the New King James Version. Copyright © 1979, 1980, 1982 by Thomas Nelson, Inc. Used by permission. All rights reserved.
All information contained in Clarifying Christianity is a resource for questions dealing with Christian issues. It is not to be taken as Christian counseling. Seek a qualified Christian counselor for help with all such issues. If you choose to work with a Christian counselor, it is your responsibility to ask pertinent questions before you begin, to assure yourself of their qualities and abilities.1539