Tag Archives: Science

Book review of R.C. Sproul’s “If there’s a God, why are there atheists?”

I have a key that will unlock a puzzling mystery
I have a key that will unlock a puzzling mystery

Brian Auten has a book review posted up at Apologetics 315.

The book is “If There’s A God, Why Are There Atheists?”, by theologian R.C. Sproul. R.C. Sproul is one of my favorite theologians. The book in question has a very, very special place in my heart, because I think that it is one of the major reasons why I was able to resist pernicious ideas like religious pluralism and postmodernism for so long. Once you put on the glasses of Romans 1 and see for the first time what man is really doing with respect to God, you can never see things the same again. I’ll say more about this at the end, but let’s see what Brian wrote first.

The review

So often, you hear atheists complaining about religion is nothing but wish-fulfillment or some sort of crutch for people who are frightened by a variety of things. They think that God is invented to solve several problems. 1) how does the world work?, 2) is there meaning to suffering and evil?, 3) why should I be moral?, and 4) what will happen to me and my loved ones when I die?. On the atheistic view, God is just a crutch that people cling to out of weakness and ignorance. But is this really the case?

Sproul starts the book by investigating three atheists who sought to explain religious belief as a result of psychological factors.

Brian writes:

Before tackling the psychology of atheism, Sproul spends a chapter on the psychology of theism, from the perspective of Freud’s question “If there is no God, why is there religion?”11 What follows is an overview of various psychological explanations of theistic belief: Feuerbach’s “religion is a dream of the human mind.”12 Marx’s belief that religion is “due to the devious imagination of particular segment of mankind.”13 And Nietzche’s idea that “religion endures because weak men need it.”14 The author properly reiterates: “We must be careful to note that the above arguments can never be used as proof for the nonexistence of God. They can be useful for atheists who hear theists state that the only possible explanation for religion is the existence of God.”15 That being said, Sproul also reveals what these arguments presume:

Their arguments already presupposed the nonexistence of God. They were not dealing with the question, Is there a God? They were dealing with the question, Since there is no God, why is there religion?16

Sproul points out the weaknesses of each of these approaches and says “there are just as many arguments showing that unbelief has its roots in the psychological needs of man.”

Wow, could that really be true? What are the real reasons why people reject God? Does the Bible have anything to say about what those reasons are?

Brian cites Sproul’s contention:

The New Testament maintains that unbelief is generated not so much by intellectual causes as by moral and psychological ones. The problem is not that there is insufficient evidence to convince rational beings that there is a God, but that rational beings have a natural hostility to the being of God.

[…]Man’s desire is not that the omnipotent, personal Judeo-Christian God exist, but that He not exist.

In Romans 1:18-23, the apostle Paul explains what is really going on:

18The wrath of God is being revealed from heaven against all the godlessness and wickedness of men who suppress the truth by their wickedness,

19since what may be known about God is plain to them, because God has made it plain to them.

20For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that men are without excuse.

21For although they knew God, they neither glorified him as God nor gave thanks to him, but their thinking became futile and their foolish hearts were darkened.

22Although they claimed to be wise, they became fools

23and exchanged the glory of the immortal God for images made to look like mortal man and birds and animals and reptiles.

On this blog, I regularly present many, many arguments for theism in general, and Christian theism in particular:

Sproul explains why atheists cannot allow themselves to live according to the evidence that is presented to them:

The cumulative effect of this knowledge that is clearly seen is to leave men ‘without excuse.’ Herein lies the basis of the universal guilt of man. No one can claim ignorance of the knowledge of God. No one can cite insufficient evidence for not believing in God. Though people are not persuaded by the evidence, this does not indicate an insufficiency in the evidence, but rather an insufficiency in man.

[…]The basic stages of man’s reaction to God can be formulated by means of the categories of trauma, repression, and substitution.

[…]If God exists, man cannot be a law unto himself. If God exists, man’s will-to-power is destined to run head-on into the will of God.

And this is the force that is animating atheists today. They don’t want to be accountable to God in a relationship, no matter what the evidence is. They have to deny it, so that they can be free to get the benefits of a universe designed for them, without having to give any recognition or acknowledgement back. If they have to lie to themselves to deny the evidence, they will do it. Anything to insulate themselves from the Creator and Designer who reveals himself in Jesus Christ.

The rest of the book review, and the book, deals with explaining in detail how atheists respond to an all-good, all-powerful, all-knowing Creator/Designer. I encourage you to click through and read the whole book review. You can read the review, and the book, and then investigate for yourself whether atheists really are like that.

My survey of atheists

By the way, did you all see my survey of atheists that I did a while back? It’s relevant because one of the questions I asked to my volunteers was “How you begin to follow Christ if it suddenly became clear to you that Christianity was objectively true?”. I got some very strange responses that dovetail nicely with Sproul’s book.

Here are a few of the responses:

  • I would not follow. My own goals are all that I have, and all that I would continue to have in that unlikely situation. I would not yield my autonomy to anyone no matter what their authority to command me.
  • I would not follow, because God doesn’t want humans to act any particular way, and he doesn’t care what we do.
  • I would not follow. Head is spinning. Would go to physician to find out if hallucinating.
  • I hope I would be courageous enough to dedicate my life to rebellion against God.
  • I would not have to change anything unless forced to and all that would change is my actions not my values.  I would certainly balk at someone trying to force me to change my behavior as would you if you were at the mercy of a moral objectivist who felt that all moral goodness is codified in the Koran.
  • He would have to convince me that what he wants for me is what I want for me.

This is all part of my series discussing whether morality is rationally grounded by atheism.

Well Spent Journey did a similar survey of atheists, inspired by mine, and got this result on the relevant question:

12. How would you begin to follow Jesus if it became clear to you that Christianity was true?

– Would follow (5)
– Wouldn’t follow (6)
Might follow the teachings of Jesus, but that isn’t Christianity (2)
– It would depend on how this truth was revealed (3)
– Christianity can’t be true (3)
– No answer given (4)

…What would be the hardest adjustment you would have to make to live a faithful, public Christian life?

– Adjusting wouldn’t be that difficult; would eagerly welcome knowing that Christianity was true (2)
– Praying, since it seems weird, creepy, and strange
– Trying to figure out how the Bible became so corrupted

– Trying to convince myself that the God of the Bible is deserving of worship (2)
– Don’t think it would be possible to adjust

– No clear response, or not applicable (16)

Yes, they really think like that! Just ask an atheist questions and you’ll see how “objective” they really are. Atheism is entirely psychological. It’s adopted in order to feel sufficient and to operate with autonomy, with the goal of self-centered pleasure-seeking above all. Evidence has nothing to do with it.

Michael Strauss lectures on scientific evidence for a Creator at UT Dallas

Christianity and the progress of science
Christianity and the progress of science

The lecture: (from 2013)

Note: there is a period of 19 minutes of Q&A at the end of the lecture.

About the speaker:

His full biography is here.

Summary:

  • It used to be true that most of the great scientists were believers in God
  • But now science has advanced and we have better instruments – is it still true?
  • Today, many people believe that science has shows that the universe and Earth are not special
  • We used to believe that the Earth was the center of the universe, and Darwin showed we are not designed
  • The problem with this view is that it is based on old science, not modern science
  • Three topics: origin of the universe, fine-tuning of the universe, the Rare Earth hypothesis

Experimental evidence for the origin of the universe:

  • #1: Hubble discovered that the universe expands because of redshifting of light from distant galaxies
  • #2: Measurements of the cosmic microwave background radiation show the universe had a beginnning
  • #3: Measurements of the light element (hydrogen and helium) abundances confirm an origin of the universe
  • The best explanation for an absolute origin of space, time, matter and energy is a supernatural cause

Experimental evidence for the design of the universe:

  • #1: The amount of matter: a bit less = no stars and galaxies, a bit more = universe recollapses
  • #2: The strong force: a bit more = only hydrogen, a bit more = little or no hydrogen
  • #3: Carbon resonance level: a bit higher = no carbon, a bit lower = no carbon

Experimental evidence for galactic, stellar and planetary habitability:

  • #1: Galaxy: produces high number of heavy elements and low radiation
  • #2: Star: long stable lifetime, burns bright, bachelor star, third generation star (10 billion years must elapsed),
  • #3: Planet: mass of planet, stable orbit, liquid water, tectonic activity, tilt, moon

Naturalistic explanations:

  • Humans evolve to the point where they reach back in time and create finely-tuned universe
  • Eternally existing multiverse

Hawking and Mlodinow response to Rare Earth:

  • There are lots of planets so one must support life
  • Odds of a planet that supports life are low even with 10^22 planets

Hawking and Mlodinow proposal of M-theory multiverse:

  • There is no experimental evidence for M-theory being true
  • M-theory is not testable now and is not likely to be testable in the future
  • But science is about making testable predictions, not about blind speculation

Hawking and Mlodinow no-boundary proposal:

  • This theory requires the laws of physics to exist prior to the universe
  • But where do you get laws of physics before there is any physical world?
  • There is no experimental evidence for no-boundary proposal
  • All the evidence we have now (redshift, CMBR, H-He abundances) is for Big Bang

What science has revealed provide abundant evidence for a transcendent Creator and Designer.

Related posts

Is belief in a Creator / Designer compatible with belief in Darwinian evolution?

Sherlock Holmes and John Watson: let's take a look at the facts
Sherlock Holmes and John Watson: let’s take a look at the facts

What should we make of theistic evolutionists telling us that you can believe in God, while still knowing that matter, law and chance fully explain the development of all of biological life?

Consider this quotation from Phillip E. Johnson.

Quote:

The National Academy’s way of dealing with the religious implications of evolution is akin to the two-platoon system in American football. When the leading figures of evolutionary science feel free to say what they really believe, writers such as Edward O. Wilson, Richard Dawkins, Daniel Dennett, Carl Sagan, Steven Pinker, Stephen Jay Gould, Richard Lewontin and others state the “God is dead” thesis aggressively, invoking the authority of science to silence any theistic protest. That is the offensive platoon, and the National Academy never raises any objection to its promoting this worldview.

At other times, however, the scientific elite has to protect the teaching of the “fact of evolution” from objections by religious conservatives who know what the offensive platoon is saying and who argue that the science educators are insinuating a worldview that goes far beyond the data. When the objectors are too numerous or influential to be ignored, the defensive platoon takes the field. That is when we read those spin-doctored reassurances saying that many scientists are religious (in some sense), that science does not claim to have proved that God does not exist (but merely that he does not affect the natural world), and that science and religion are separate realms which should never be mixed (unless it is the materialists who are doing the mixing). Once the defensive platoon has done its job it leaves the field, and the offensive platoon goes right back to telling the public that science has shown that “God” is permanently out of business.

(Phillip E. Johnson: “The Wedge of Truth”, IVP 2000, pp. 88-89).

So what naturalistic scientists believe is that God didn’t do anything to create the diversity of life – that nature does all of its own creating without God. In fact, it doesn’t matter if the best naturalistic explanation is improbable or implausible – naturalists must bitterly cling to materialistic explanations of natural phenomena. Any doubts about the efficacy of naturalistic mechanisms get met by “theistic evolutionists” – scientists who think that science shows that God didn’t do anything in the history of life.

When it comes to discussing origins, you have to be very careful with theistic evolutionists. The one question they want to avoid is whether science, done in the ordinary naturalistic way, can discover evidence of intelligent agency in the history of the development of life. And that’s why you have to ask them that question first. “Is there any scientific evidence that intelligent causes were active during the history of the development of life on this planet?” Their answer to that is the same as atheists, namely: “there is no scientific evidence that intelligent causes are responsible for the effects we see in the history of life on Earth”. Theistic evolutionists and atheists agree on that: as far as pure scientific evidence is concerned, nature can do its own creating without any intelligence writing genetic code or engineering animal body plans.

Now, take a look at this article by Jay Richards. He cites some theistic evolutionists.

Excerpt:

Biologist Ken Miller:

For his part, [Ken] Miller, a biologist, has no qualms about telling us what God would do: “And in Catholicism, he said, God wouldn’t micromanage that way. ‘Surely he can set things up without having to violate his own laws.'”

I am unaware of any tenet of Catholic theology that requires God not to micromanage. It is, however, a tenet of deism.

Got that? What really happened is that God didn’t do anything. How does he know that? From the science? No. Because he assumes naturalism. Oh, it’s true that he says that God is lurking somewhere behind the material processes that created life. But God’s agency is undetectable by the methods of science. And he is hoping that you will accept his subjective pious God-talk as proof that a fundamentally atheistic reality is somehow reconcilable with a robust conception of theism.

More from Richards:

Then we get Stephen Barr offering his private definition of “chance.”

It is possible to believe simultaneously in a world that is shaped by chance and one following a divine plan. “God is in charge and there’s a lot of accident,” said Barr, also a Catholic. “It’s all part of a plan. . . . God may have known where every molecule was going to move.”

What does Barr really believe? He believes that what science shows is that nature created life without any interference by an intelligent agent. Barr then offers believers his subjective pious God-talk to reassure them that evolution is compatible with religion. He has a personal belief – NOT BASED ON SCIENCE – that the material processes that created all of life are “all part of a plan”. He cannot demonstrate that from science – it’s his faith commitment. And more speculations: “God may have known…”. He can’t demonstrate that God did know anything from science. He is just offering a personal opinion about what God “could have” done. The purpose of these subjective opinions is to appease those who ask questions about what natural mechanisms can really create. Can natural causes really account for the development of functional proteins? Never mind that – look at my shiny spiritual-sounding testimony!

That’s theistic evolution. What really happened is that no intelligent causes are needed to explain life. What they say is “God could” and “God might” and “I pray” and “I attend this church” and “I received a Christian award” and “I sing praise hymns in church”. None of these religious opinions and speculations are relevant to the science – they are just opinions, speculations and biographical trivia. Atheists and theistic evolutionists agree on what science shows about the diversity of life – intelligent causes didn’t do anything.

Front-loading?

One of the ways that theistic evolutionists try to affirm design is by insisting that the design is “front-loaded”. The design for all the information and body plans is somehow embedded in matter.

Here is Stephen C. Meyer to assess that:

It’s very important to understand that there is no scientific evidence for design (information) being front-loaded. So although the theistic evolutionists are talking about design, it’s still in the realm of faith – not detectable to scientific investigation. And as Dr. Meyer explained, it doesn’t work to explain design anyway.

I attended a Wheaton College philosophy conference where Dr. Michael Murray read a paper advocating for this front-loaded view of design. I raised my hand to ask him a question, “hey, philosophy guy, did God front-load the information in that paper you’re reading, or did you write it yourself?” But the philosophy moderators must have known that I was an engineer, and would talk sense into him, because they never called on me. However, I did e-mail him later and asked him if he had any evidence for this front-loading theory, and couldn’t God write sequence information in time the same way he had sequenced information in his essay. He replied and said that front-loading was more emotionally satisfying for him. That’s philosophy, I guess. Thank goodness an engineer wrote his e-mail program so that he could at least come clean about his silly view.

The quickest way to disarm a theistic evolutionist is to ask them for a naturalistic explanation of the origin of life. And for a naturalistic explanation of the Cambrian explosion. And so on. Focus on the science – don’t let them turn the conversation to their personal beliefs, or to the Bible, or to religion. No one cares about the psychology of the theistic evolutionist. We only care what science can show.

How the WMAP satellite confirmed nucleosynthesis predictions and falsified atheism

Christianity and the progress of science
Christianity and the progress of science

Prior to certain scientific discoveries, most people thought that the universe had always been here, and no need to ask who or what may have caused it. But today, that’s all changed. Today, the standard model of the origin of the universe is that all the matter and energy in the universe came into being in an event scientists call “The Big Bang”. At the creation event, space and time themselves began to exist, and there is no material reality that preceded them.

So a couple of quotes to show that.

An initial cosmological singularity… forms a past temporal extremity to the universe. We cannot continue physical reasoning, or even the concept of spacetime, through such an extremity… On this view the big bang represents the creation event; the creation not only of all the matter and energy in the universe, but also of spacetime itself.

Source: P. C. W. Davies, “Spacetime Singularities in Cosmology,” in The Study of Time III, ed. J. T. Fraser (Berlin: Springer Verlag ).

And another quote:

[A]lmost everyone now believes that the universe, and time itself, had a beginning at the big bang.

Source: Stephen Hawking and Roger Penrose, The Nature of Space and Time, The Isaac Newton Institute Series of Lectures (Princeton, N. J.: Princeton University Press, 1996), p. 20.

So, there are several scientific discoveries that led scientists to accept the creation event, and one of the most interesting and famous is the discovery of how elements heavier than hydrogen were formed.

Nucleosynthesis: forming heavier elements by fusion
Nucleosynthesis: forming heavier elements by fusion

Here’s the history of how that discovery happened, from the National Aeronautics and Space Administration (NASA) web site:

The term nucleosynthesis refers to the formation of heavier elements, atomic nuclei with many protons and neutrons, from the fusion of lighter elements. The Big Bang theory predicts that the early universe was a very hot place. One second after the Big Bang, the temperature of the universe was roughly 10 billion degrees and was filled with a sea of neutrons, protons, electrons, anti-electrons (positrons), photons and neutrinos. As the universe cooled, the neutrons either decayed into protons and electrons or combined with protons to make deuterium (an isotope of hydrogen). During the first three minutes of the universe, most of the deuterium combined to make helium. Trace amounts of lithium were also produced at this time. This process of light element formation in the early universe is called “Big Bang nucleosynthesis” (BBN).

The creation hypothesis predicts that there will be specific amounts of these light elements formed as the universe cools down. Do the predictions match with observations?

Yes they do:

The predicted abundance of deuterium, helium and lithium depends on the density of ordinary matter in the early universe, as shown in the figure at left. These results indicate that the yield of helium is relatively insensitive to the abundance of ordinary matter, above a certain threshold. We generically expect about 24% of the ordinary matter in the universe to be helium produced in the Big Bang. This is in very good agreement with observations and is another major triumph for the Big Bang theory.

Moreover, WMAP satellite measurements of mass density agree with our observations of these light element abundances.

Here are the observations from the WMAP satellite:

Scientific observations match predictions
Scientific observations match predictions

And here is how those WMAP measurements confirm the Big Bang creation event:

However, the Big Bang model can be tested further. Given a precise measurement of the abundance of ordinary matter, the predicted abundances of the other light elements becomes highly constrained. The WMAP satellite is able to directly measure the ordinary matter density and finds a value of 4.6% (±0.2%), indicated by the vertical red line in the graph. This leads to predicted abundances shown by the circles in the graph, which are in good agreement with observed abundances. This is an important and detailed test of nucleosynthesis and is further evidence in support of the Big Bang theory. 

“An important and detailed test”.

For completeness, we should learn how elements heavier than these light elements are formed:

Elements heavier than lithium are all synthesized in stars. During the late stages of stellar evolution, massive stars burn helium to carbon, oxygen, silicon, sulfur, and iron. Elements heavier than iron are produced in two ways: in the outer envelopes of super-giant stars and in the explosion of a supernovae. All carbon-based life on Earth is literally composed of stardust.

That’s a wonderful thing to tell a young lady when you are on a date: “your body is made of stardust”. In fact, as I have argued before, this star formation, which creates the elements necessary for intelligent life, can only be built if the fundamental constants and quantities in the universe are finely-tuned.

Now, you would think that atheists would be happy to find observations that confirm the origin of the universe out of nothing, but they are not. Actually, they are in denial.

Here’s a statement from the Secular Humanist Manifesto, which explains what atheists believe about the universe:

Religious humanists regard the universe as self-existing and not created.

For a couple of examples of how atheistic scientists respond to the evidence for a cosmic beginning, you can check out this post, where we get responses from cosmologist Lawrence Krauss, and physical chemist Peter Atkins.

You cannot have the creation of the universe be true AND a self-existing, eternal universe ALSO be true. Someone has to be wrong. Either the science is wrong, or the atheist manifesto is wrong. I know where I stand.

Positive arguments for Christian theism

How the discovery of the cosmic microwave background radiation falsified atheism

Christianity and the progress of science
Christianity and the progress of science

Prior to certain scientific discoveries, most people thought that the universe had always been here, and no need to ask who or what may have caused it. But today, that’s all changed. Today, the standard model of the origin of the universe is that all the matter and energy in the universe came into being in an event scientists call “The Big Bang”. At the creation event, space and time themselves began to exist, and there is no material reality that preceded them.

So a couple of quotes to show that.

An initial cosmological singularity… forms a past temporal extremity to the universe. We cannot continue physical reasoning, or even the concept of spacetime, through such an extremity… On this view the big bang represents the creation event; the creation not only of all the matter and energy in the universe, but also of spacetime itself.

Source: P. C. W. Davies, “Spacetime Singularities in Cosmology,” in The Study of Time III, ed. J. T. Fraser (Berlin: Springer Verlag ).

And another quote:

[A]lmost everyone now believes that the universe, and time itself, had a beginning at the big bang.

Source: Stephen Hawking and Roger Penrose, The Nature of Space and Time, The Isaac Newton Institute Series of Lectures (Princeton, N. J.: Princeton University Press, 1996), p. 20.

So, there are several scientific discoveries that led scientists to accept the creation event, and one of the most interesting and famous is the discovery of the cosmic microwave background radiation.

Here’s the history of how that discovery happened, from the American Physical Society web site:

Bell Labs radio astronomers Arno Penzias and Robert Wilson were using a large horn antenna in 1964 and 1965 to map signals from the Milky Way, when they serendipitously discovered the CMB. As written in the citation, “This unexpected discovery, offering strong evidence that the universe began with the Big Bang, ushered in experimental cosmology.” Penzias and Wilson shared the Nobel Prize in Physics in 1978 in honor of their findings.

The CMB is “noise” leftover from the creation of the Universe. The microwave radiation is only 3 degrees above Absolute Zero or -270 degrees C,1 and is uniformly perceptible from all directions. Its presence demonstrates that that our universe began in an extremely hot and violent explosion, called the Big Bang, 13.7 billion years ago.

In 1960, Bell Labs built a 20-foot horn-shaped antenna in Holmdel, NJ to be used with an early satellite system called Echo. The intention was to collect and amplify radio signals to send them across long distances, but within a few years, another satellite was launched and Echo became obsolete.2

With the antenna no longer tied to commercial applications, it was now free for research. Penzias and Wilson jumped at the chance to use it to analyze radio signals from the spaces between galaxies.3 But when they began to employ it, they encountered a persistent “noise” of microwaves that came from every direction. If they were to conduct experiments with the antenna, they would have to find a way to remove the static.

Penzias and Wilson tested everything they could think of to rule out the source of the radiation racket. They knew it wasn’t radiation from the Milky Way or extraterrestrial radio sources. They pointed the antenna towards New York City to rule out “urban interference”, and did analysis to dismiss possible military testing from their list.4

Then they found droppings of pigeons nesting in the antenna. They cleaned out the mess and tried removing the birds and discouraging them from roosting, but they kept flying back. “To get rid of them, we finally found the most humane thing was to get a shot gun…and at very close range [we] just killed them instantly. It’s not something I’m happy about, but that seemed like the only way out of our dilemma,” said Penzias.5 “And so the pigeons left with a smaller bang, but the noise remained, coming from every direction.”6

At the same time, the two astronomers learned that Princeton University physicist Robert Dicke had predicted that if the Big Bang had occurred, there would be low level radiation found throughout the universe. Dicke was about to design an experiment to test this hypothesis when he was contacted by Penzias. Upon hearing of Penzias’ and Wilson’s discovery, Dicke turned to his laboratory colleagues and said “well boys, we’ve been scooped.”7

Although both groups published their results in Astrophysical Journal Letters, only Penzias and Wilson received the Nobel Prize for the discovery of the CMB.

The horn antenna was designated a National Historic Landmark in 1990. Its significance in fostering a new appreciation for the field of cosmology and a better understanding of our origins can be summed up by the following: “Scientists have labeled the discovery [of the CMB] the greatest scientific discovery of the 20th century.”8

It’s the greatest scientific discovery of the 20th century.

In the New York Times, Arno Penzias commented on his discovery – the greatest discovery of the 20th century – so:

The best data we have [concerning the Big Bang] are exactly what I would have predicted, had I nothing to go on but the five books of Moses, the Psalms, the bible as a whole.

Just one problem with the greatest scientific discovery of the 20th century: atheists don’t accept it. Why not?

Here’s a statement from the Secular Humanist Manifesto, which explains what atheists believe about the universe:

Religious humanists regard the universe as self-existing and not created.

For a couple of examples of how atheistic scientists respond to the evidence for a cosmic beginning, you can check out this post, where we get responses from cosmologist Lawrence Krauss, and physical chemist Peter Atkins.

You cannot have the creation of the universe be true AND a self-existing, eternal universe ALSO be true. Someone has to be wrong. Either the science is wrong, or the atheist manifesto is wrong. I know where I stand.

Positive arguments for Christian theism