We've got a problem because the age of the Universe is 13.75 billion years plus or minus 170 million years. This number is not a guess, but the result of remarkably accurate measurements by the Wilkinson Microwave Anisotropy Probe (WMAP) team that are corroborated by data from the Hubble Space Telescope; the Cosmic Background Explorer; the Spitzer Space Telescope; the large ground-based telescopes, including the radio telescopes; and numerous discoveries that span more than a thousand years and a wide range of scientific disciplines. The age given above is a refinement announced in early 2010 by the Stanford Linear Accelerator Center (SLAC National Accelerator Laboratory). Deep Time—the realization that the Earth is ancient and that the Universe is even more ancient—may be counted among the greatest of human intellectual achievements. We've got a problem because there are substantial numbers of Americans who have little or no knowledge of the World they live in. This renders them incapable of comprehending modern society and understanding the technological and political issues of the day. Some of them are trying to substitute a certain religious dogma for the teaching of scientific truth in America's public schools. Their dogma on the age of the Universe and the age of the Earth is dead wrong, so we are fortunate that it is unconstitutional to teach religious dogma in the public schools. These people aren't satisfied with spreading their false beliefs in their own churches, schools, and homes; they want to cram them down the throat of every American. The prosperity of the United States and the other liberal democracies in the world and the freedoms we all enjoy are intimately and inextricably tied to advances in liberal education, scientific research, exploration, and discovery on the part of progressive, independent thinkers. The end of legitimate scientific inquiry, untinged by dogma and superstition, would signal the end of the civilized world.

One of the many ways that we know the Universe is very old is the indisputable evidence in this photograph that there is nothing unusual about the galaxy we live in—it has billions of counterparts throughout the Universe. Our galaxy, the Milky Way, contains about 400 billion stars. This is not a guess, either, but a very reasonable estimate based upon sound science. We know the diameter of our galaxy (about 100,000 light years) and the orbital velocity of many stars, and to know those parameters is to know the mass of our galaxy. To know the mass is the key to making a reliable estimate of the number of stars in the galaxy because there are upper and lower constraints on the masses of stars. The number of bright galaxies in our Hubble Volume—that part of the Universe that we can see and explore with our instruments—is also about 100 billion. We don’t know the number of distant dim galaxies that we cannot see, but it must be vast. Some of the bright galaxies are larger than the Milky Way and some are smaller. It is reasonable to estimate that they have about 400 billion stars each. (Though the nearest large galaxy to us, the Andromeda Galaxy, or M31, is twice the diameter of the Milky Way and contains a trillion stars. It takes light about 2.5 million years to travel from M31 to our telescopes.)

Update, December 8, 2009—The Space Telescope Science Center has released a new Hubble Deep Field Image that was made with The Hubble Space Telescope’s newly installed Wide Field Camera 3. The new images shows galaxies that are more than 13 billion years old.

The claim that the Universe is 6,000 years old is not simply inaccurate; it is so far off the mark as to be nonsensical. If the Universe were 6,000 years old, all the matter in the Universe—the 400 billion stars in our galaxy and the 400 billion stars in each of the 100 billion bright galaxies in our Hubble volume—would be contained in a sphere 6,000 light years in diameter. If that were true then the stars—including our sun—could be no larger than the smallest known subatomic particle. It would mean that we are wrong about the size of the Earth and everything on it. Since the sun has a volume of about 1.3 million Earths, the Earth would have to be at least 1.3 million times smaller than the smallest known subatomic particles. The claim is nonsensical because a 6,000-year-old universe would contain no stars, no planets, no people; it would be a Universal Black Hole. Our experience tells us that it is not.

If the Universe were 6,000 years old, everything we think we understand in science—everything—would be wrong. We don’t know the speed of light. The theory of gravity is invalid (watch out for upward-falling apples!) We don't know about stars. Atoms don’t exist, so all of chemistry is wrong. Wheels don’t turn, rulers don’t measure distance, clocks don’t measure time, we have no understanding of mathematics. We can't generate electricity or develop a polio vaccine. We can’t even enumerate the fingers on our hands. And your cell phone—a quantum mechanical device whose design uses the same fundamental theories that reveal the true age of the Universe—doesn’t work.

In short, the Universe cannot exist if the Universe is 6,000 years old. If the Universe cannot exist if it is 6,000 years old, then—if we accept that the Universe exists—the Universe cannot be 6,000 years old.

The measured age of the Universe, 13.75 billion years plus or minus 170 million years, may continue to be refined as new precision measuring tools are developed, but the number is unlikely to change to a great degree. At the beginning of 2008 the age was given as 13.7 billion years within a one percent margin of error. A refinement of some millions of years was announced in March, 2008, reflecting the continuing analysis of WMAP data. Another refinement, to the number presented above, was announced in early 2010. There is a limit to how far the measurement can be refined, however; the WMAP team is not going to announce that the Universe came into being at 3:18 p.m. on a fine Monday in May (but see Bishop Ussher below).

What is the age of the Earth?

Radiometric dating has shown that the Earth is around 4.54 billion years old. The oldest minerals that have been found in meteorites that are known from their chemical composition to have formed with the Solar System are 4.567 billion years old. Thus, the Earth cannot be older than that. The oldest minerals that are known to have formed on Earth are zircons from Western Australia that have been dated using radiometric dating. They are 4.4 billion years old. Thus the Earth is older than 4.4 billion years and younger than 4.567 billion years. The amount of time required for the materials that comprise the Earth to accrete from the primordial disk that became the Solar System is not known with high precision. Thus, 4.54 billion years is a very reasonable estimate, not far off the mark. The same cannot be said for the late Bishop Ussher's “measurement.”

In 1650 Bishop James Ussher, a scholar and an Anglican theologian, announced that the world was created on Sunday, October 23, 4004 BC. He based his conclusion on laborious calculation of the ages and reigns of kings in the Bible. Isaac Newton, one of the greatest scholars who ever lived, agreed with the Bishop. The Bishop and Newton were wrong.

Neither Ussher nor Newton was a geologist. James Hutton, however, was a geologist—the father of modern geology, in fact. Hutton was born in Edinburgh in 1726, less than a year after Newton's death. Hutton was fascinated by the geology of Britain, and it was his publication of The Theory of the Earth in 1787 that made him the father of modern geology. In a nutshell, here's what Hutton did. He realized that the presence of marine fossils high in mountain ranges meant that the rock from which those mountains were made had to have been ocean bottom at one time, and that geological forces had turned that ocean bottom into rock and pushed that rock upward until it became mountains, high above the oceans. He also recognized that mountains wear down due to erosion from water and wind, and the residue—sand—finds its way back to the ocean, where the process is repeated. Hutton knew that this process did not happen in a short time—certainly not as short at 6,000 years—because he had studied ancient maps and he knew that there had been no appreciable change in Britain's coastlines, rivers, or mountains in recorded history. Hutton's huge intellectual achievement marked the beginning of the discovery of Deep Time—the knowledge that the Earth is ancient. Hutton could not know how ancient, because knowledge of the decay rate of radioisotopes lay over a hundred years in the future. If Hutton and all the geologists who came afterward were wrong we would observe the appearance and disappearance of mountain ranges, canyons, rivers, lakes, and oceans in the duration of a human lifetime. Such a planet would be a dangerous, and probably uninhabitable, place.

Astronomers are Time Travelers

A light year (LY) is the distance that a photon travels in a straight line in one year. The photon, by definition, travels through a vacuum at the speed of light, which is about 300,000 km (186,000 miles) per second. Thus, the light year is a measure of distance.

When we say that M31, the Andromeda Galaxy, is 2.5 million light years distant it means that it required the cumulative light from the stars in M31 2.5 million years to reach the earth. You are seeing M31 as it looked 2.5 million years ago. If you want to see it as it looks today you will have to wait 2.5 million years (a little bit less, actually, because M31 is moving toward us and will most likely collide with our galaxy in about 3 billion years.)

Likewise, if M31 were to disappear into a Black Hole today (it will not) we would not know about it for about 2.5 million years. M31 is visible to the unaided eye under dark skies as a faint gray patch. I have even seen it a number of times from my home in light-polluted Maryland. M31 is generally cited as the most distant object that the human eye can see without optical aid. As far as I know, that is true.

You don't have to look at M31 to look into the past, however. Look at the Moon. You are seeing it as it was about 1-1/2 seconds ago. Look at the Sun (briefly!) and you are seeing it as it was eight minutes ago. Look at your spouse across the dinner table and you are seeing her as s/he was about five billionths of a second earlier. It would not be convenient to compute or estimate the actual time of the occurrence of a distant astronomical event such as a supernova in a distant galaxy. So, if a supernova (SN) in a galaxy 168,000 LY distant was discovered on February 23, 1987 we would describe it as SN 1987 (followed by an ordinal letter). In fact, there was such a supernova, and it is known as SN 1987A.