God: The Failed Hypothesis (20 page)

Is the Vacuum Energy Fine-Tuned?

Next, let us examine the claim that the vacuum energy of the universe is fine-tuned. Normally we think of the vacuum as being empty of matter and energy. However, according to general relativity, gravitational energy can be stored in the curvature of empty space. Furthermore, quantum mechanics implies that a vacuum could contain a minimum
zero-point energy.

Weinberg referred to this as the
cosmological constant problem,
since any vacuum energy density is equivalent to the parameter in Einstein’s theory of general relativity called the cosmological constant that relates to the curvature of empty space-time
³⁴
. A better term is
vacuum energy problem.

Crude calculations gave a value for the vacuum energy density that is some 120 orders of magnitude greater than its maximum value from observations. Since this density is constant, it would seem to have been fine-tuned with this precision from the early universe, so that its value today allowed for the existence of life.

Until recent years, it was thought that the cosmological constant is exactly zero, in which case there was no need for finetuning, although no theoretical reason was known. However, in 1998, two independent research groups studying distant supernovae were astonished to discover that the current expansion of the universe is
accelerating
³⁵
.
More recent observations from other investigators have confirmed this result. The universe is falling up! The source of this cosmic acceleration may be some still-unidentified
dark energy,
which constitutes 70 percent of the mass of the universe. One possible mechanism is gravitational repulsion by means of the cosmological constant, that is, by way of a vacuum energy field, which is allowed by general relativity.

If that is the case, then the cosmological constant problem resurfaces. In the meantime, we now have plausible reasons to suspect that the original calculation was incomplete and that a proper calculation will give zero for the vacuum energy density
³⁶
.

Until these newer estimates are shown to be wrong, we cannot conclude that the vacuum is fine-tuned for life and we have no particularly strong need to invoke a designer deity.

But, then, what is responsible for cosmic acceleration, that is, what is the nature of the dark energy? A cosmological constant is not the only possible source of gravitational repulsion. According to general relativity, any matter field will be repulsive if its pressure is sufficiently negative. Theorists have proposed that the dark energy may be a matter field, called
quintessence,
which requires no fine-tuning
³⁷
. Finally, it should be noted that cosmologists are still not totally convinced that dark energy must be invoked to account for the observed cosmic acceleration and have proposed alternate mechanisms.

Other Forms of Life?

Carbon would seem to be the chemical element best suited to act as the building block for the type of complex molecular systems that develop lifelike qualities. Even today, new materials assembled from carbon atoms exhibit remarkable, unexpected properties, from superconductivity to ferromagnetism. We expect any life found in our universe to be carbon-based, or at least based on heavy element chemistry.

But that need not be true in every conceivable universe. Even if all the forms of life discovered in our universe turn out to be of the same basic structure, it does not follow that life is impossible under any other arrangement of physical laws and constants.

According to the scenario I mentioned briefly in the last chapter, certain laws of physics are likely to be common to any universe born out of empty space-time, but others along with many physical constants may be the result of a random process called spontaneous symmetry breaking.

The possibility of other laws and constants is fatal to the fine-tuning argument. Philosopher Gilbert Fulmer has shown that the fine-tuning argument is logically incoherent
³⁸
. Simplifying his more detailed analysis, the fine-tuning argument requires that the set of facts for our universe, {Ul}, could have been a different set, {U2}. But in that case, we cannot use {Ul}, which is all we know, to say anything about {U2}. (See epigraph to this chapter by David Hume.)

We can only speculate what form life might take on another planet, with different conditions. It would be wonderful to have more examples of life, but we do not. And, any speculation about what form life might take in a universe with a different electron mass, electromagnetic interaction strength, or different laws of physics is even more problematical. We simply do not have the knowledge to say whether life of
some
sort would not occur under different circumstances.

Theists who argue that the universe is fine-tuned to earthly life have the burden of proving that no other form of life is possible, not just on other planets in our universe but in every conceivable universe that has different physical parameters. They have provided no such proof and it would seem that such a proof is impossible.

In fact, the whole argument from fine-tuning ultimately makes no sense. As my friend Martin Wagner notes, all physical parameters are irrelevant to an omnipotent God. “He could have created us to live in hard vacuum if he wanted
³⁹
.”

Waste

The anthropic argument for the existence of God can be turned on its head to provide an argument against the existence of God. If God created a universe with at least one major purpose being the development of
human
life, then it is reasonable to expect that the universe should be congenial to
human
life. Now, you might say that God may have had other purposes besides humanity. As has been noted several times in this book, apologists can always invent a god who is consistent with the data. One certainly can imagine a god for whom humanity is not very high on the agenda and who put us off in a minuscule, obscure corner of the universe.

However, this is not the God of Judaism, Christianity, and Islam, who places great value on the human being and supposedly created us in his image. Why would God send his only son to die an agonizing death to redeem an insignificant bit of carbon?

If the universe were congenial to human life, then you would expect it to be easy for humanlike life to develop and survive throughout the universe.

As we will discuss in chapter 6, the cosmological universe bears no resemblance to what is described in Genesis. Indeed, the biblical myth is more akin to what one might expect from a perfect creator. But that is not what we see. Earth is not the flat, immovable circle at the center of a firmament or a vault of fixed stars, circled by the sun, moon, and planets pictured in Genesis.

Rather, Earth is one planet among ten or so (depending on how you count) revolving around an atypical star, our sun. On the distance scale of human experience, the solar system is immense.

Earth is one hundred and fifty million kilometers from the sun.

Pluto is some six billion kilometers away. The Oort cloud of comets, which marks the edge of the solar system, extends to thirty trillion kilometers from the sun. Although the space between the planets contains smaller asteroids, comets, and dust, the solar system consists mainly of empty space that seems to serve no purpose.

On this distance scale, the planets are tiny points. Yet they are huge on the human scale. The diameter of Earth is 12,742 kilometers. The largest planet, Jupiter, is 139,822 kilometers in diameter.

Beyond the solar system we find even more space. The next closest star (after the sun), Proxima Centauri, is forty trillion kilometers away. This is part of the triple-star system called Alpha Centauri. On this scale we should start using light-years as the unit of distance, where the light-year is the distance traveled by light in a year (9.45 trillion kilometers). The Alpha Centauri system is 4.22 light-years away. Note that multiple-star systems, which are very common, do not provide the kind of orbital stability we experience on Earth that is very important to our survival. It would seem that only single-star systems are likely to support life, another indication that life is not high on the universe’s agenda.

Our sun and its planetary system are well away from the center of a galaxy containing an estimated two hundred to four hundred billion other stars. Called the “Milky Way,” after the band of stars we see across the sky on a clear night, our visible galaxy is a flat, spiral disk one hundred thousand light-years across, and about ten thousand light-years thick.

The Milky Way is but one of perhaps a hundred billion galaxies in the visible universe. We have two satellite galaxies, just outside the Milky Way, the Large and Small Magellanic Clouds. The next galaxy nearest to us, Andromeda, is 2.44 million light-years away And, you might ask, how big is the universe? The farthest observed galaxy at this writing, Abell 1835 IR1916, is 13.2 billion light-years away. Since it has taken 13.2 billion years for its light to reach us, and the current estimate of the age of the universe is 13.7 billion years, we are seeing this galaxy as it was only five hundred million years after the start of the big bang. Because the universe has been expanding since the light left Abell, this galaxy is now about forty billion light-years away.

The farthest distance we can ever hope to see, what is called our
horizon,
is 13.7 billion light-years from Earth. Beyond that, light would take longer than the age of the universe to reach us. As vast as is the universe within our horizon, cosmology suggests that a far vaster one lies beyond. If the inflationary big bang model of the early universe is correct, then in a tiny time interval (something like 10-35 second), the universe expanded in size by a factor that is almost impossible to imagine. Here is one estimate of that factor: Write down the number 1 and follow it by a hundred zeros. Then raise the number 10 to that power (10 to 10100). I have not been able to think of any analogy from common experience or science to help visualize that number. The size of the visible universe (1026 meters) is only 1061 times larger than the smallest distance mat can be defined, the Planck distance (10-35 meter).

In short, if God created the universe as a special place for humanity, he seems to have wasted an awfully large amount of space where humanity will never make an appearance.

He wasted a lot of time, too. Instead of six days, he took nine billion years to make Earth, another billion years or so to make life, and then another four billion years to make humanity.

Humans have walked on Earth for less than one-hundredth of one percent of Earth’s history.

In fact, when you think of it, why would an infinitely powerful God even need six days? Wouldn’t he have the ability to create everything in an instant? And, why would he have to rest when he was all done?

Let us also ponder the enormous waste of matter. The hundred billion galaxies, each with on the order of a hundred billion stars, are composed of “atomic matter,” that is, chemical elements. The portion that is luminous, that is, visible to the eye and optical telescopes, constitutes just one-half of one percent of all the mass in the universe. Another 3.5 percent of the matter in galaxies is of the same atomic nature, only nonluminous. Just 2

percent of atomic matter is composed of elements heavier than helium. One-half of 1 percent of this is composed of carbon, the main element of life. That is, 0.0007 of the mass of the universe is carbon. Yet we are supposed to think that God specially designed the universe so it would have the ability to manufacture, in stars, the carbon needed for life?

Still-unidentified “dark matter” makes up 26 percent of the mass of the universe, while the bulk of the universe, about 70 percent, is “dark energy,” which also remains unknown in nature but possesses no known miraculous properties. From this breakdown of mass, we see that 96 percent of the mass of the universe is not even of the type of matter associated with life.

Energy is wasted, too. Of all the energy emitted by the sun, only two photons in a billion are used to warm Earth, the rest radiating uselessly into space.

Humanity in Space

Much is made of human spaceflight. It is hyped as the search for new worlds akin to the European explorations on Earth during the Age of Discovery. Space operas like
Star Trek
and
Star Wars
lead people to think that someday all we will have to do is hop in a spaceship and cross the galaxy at warp speed. Every planet we land on is imagined to have an atmosphere and other conditions sufficiently like Earth that we will be able to walk around without spacesuits. In this way, it is widely believed, humanity will gradually populate the cosmos.

However, this is not as easy as saying, “Take over the bridge, Mr. Spock.” Let us look at some of the numbers. A spaceship moving at 11.1 kilometers per second, the escape velocity for Earth, would take 114,000 years to reach Alpha Centauri, the nearest star system beyond the solar system. That same spaceship would take three billion years to cross our galaxy. The most optimistic estimates are that earthlike planets are on average five hundred light-years apart, depending on how you define “earthlike.”

This is at least a sixteen-generation trip at speeds near the speed of light. Here, it must be emphasized, just being labeled earthlike does not mean humans could survive without life support. In fact, we are not likely to be able to survive on the great majority of such planets since the planet is not likely to be exactly like Earth in every detail needed for human survival.

Now, Einstein’s special theory of relativity makes it in principle possible to reach anyplace in the universe in the lifetime of an astronaut onboard a spacecraft. The ship just has to go fast enough relative to Earth. According to what is called
time dilation,
a moving clock is observed to run slower than one at rest. In a related effect called
Fitzgerald-Lorentz contraction,
the measured length of an object contracts in the direction of its motion. These phenomena, which defy our commonsense notions of time and space, have been amply confirmed in experiments and other observations.