Throughout most of history, the position of atheist philosophers was that the universe is eternal; the material world has just always existed. The idea that the universe started to exist implied that someone created it so they concluded that the material universe itself was ultimate and inherently necessary. It had no beginning and therefore no cause.
However, in the last hundred years, scientists have observed a number of things that lead inescapably to the conclusion that the universe is not eternal. One of the most well-established facts in physics and cosmology is that all matter in the universe and even all space and time itself began to exist at a point in the finite past. While a few people have proposed alternative theories to try and cling to a belief in an eternal universe, none of them have panned out.
If time, space, and matter all started to exist, there was obviously something that caused this to happen. Whatever that cause was, it could only be something immaterial, non-spatial, and eternal. The only things we know of that are non-spatial and immaterial are abstract entities (like numbers and logical truths) and minds. Of these, only minds act as causal agents, so it seems we are left with the inescapable conclusion that our universe was caused by an eternal, supernatural, extremely powerful mind…aka “God.”
Sometimes people try to get around this conclusion by claiming that quantum physics allows things to pop into existence from nothing. That just isn’t true. Not even virtual particles come from nothing since they are the result of fluctuations of energy in a quantum vacuum and are governed by the laws of physics. At the very least they require energy and information, and that’s not nothing.
The claim that the universe just popped into being uncaused from nothing goes against every principle of science ever established. If you believe in science, then you should probably believe in God.
In order for life to exist, there needs to be a large number of chemical elements, and in order for these to exist, there need to be planets and large stars, and in order for stars to form, the laws of physics need to be just right. That’s an incredible oversimplification because scientists have discovered dozens of these kinds of variables that need to be very finely-tuned for any of these necessary elements to exist.
For example, the nuclear efficiency of fusion from hydrogen to helium depends on the strong nuclear force and is 0.007. If this number were 0.006, only hydrogen would exist in the universe. If it were 0.008, no hydrogen would exist at all.
And that’s actually a pretty tame example. If the critical density of the universe was off by one part in 1,000,000,000,000,000, the universe would either collapse on itself or expand so quickly no planets or stars could form.
The Cosmological Constant is fine-tuned to one part in 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000.
The thing about these factors is that there’s no scientific reason for them to be finely tuned to the exact numbers that they are. Either they happened entirely by chance or they were set intentionally in order to create a universe that can sustain life (the other alternative is that an infinite number of universes with random sets of variables are constantly popping into existence from nothing. See reason one for why this is not a good solution).
Imagine I told you I hid a random atom somewhere in the universe and you have one guess to find that specific atom or the universe will stop existing…then imagine you have to do that twice in a row. Those are still better odds than the odds of our universe existing by chance. If you believe in math, you should probably believe in God.
People don’t always agree about the right thing to do in a given situation, and what we believe about “right” and “wrong” is significantly influenced by our culture and upbringing. While many of our values and ideas about morality may be subjective and relative, there seem to be some fairly universal beliefs most of us tend to agree on. Love is better than murder; kindness is better than genocide; you shouldn’t torture little kids for the fun of it…these are basic moral principles most people can get behind. In fact, every day we operate under the assumption that there are things we should and shouldn’t do, and we hold other people to similar standards.
Why do we believe in right and wrong? The most common responses argue that either 1) morality is based in the character of God who defines good and evil, or 2) there is no such thing as objective morality because what we perceive as right and wrong is based simply on social conventions, pragmatism, or evolutionary pressures. In the second view, nothing is objectively right or objectively wrong, it’s just advantageous or not advantageous (atheists have been unable to present a credible case for the existence of absolute, objective morals and virtues).
Maybe you don’t believe taking care of your children is an objectively good thing and is just something you have to do to avoid negative consequences from society. Maybe you believe slavery in the U.S. wasn’t really wrong, it’s just that a majority of people changed their opinions about it. Maybe you believe that what Hitler did wasn’t really wrong, it was just inconvenient for a lot of people. If that’s you, then the argument from objective morality isn’t going to be persuasive. But if you believe anything can be truly right or wrong, you should probably believe in God.
People who believe in God believe in some kind of non-physical reality. God can be thought of as an immaterial spirit or a supernatural mind. Most people who don’t believe in God believe that the material world is all that exists. That would mean that everything we are is just a pile of organized atoms.
In this view, what you experience as your conscious mind is simply the result of chemical reactions in your physical brain. Take this a step further and it means that everything you experience and everything you perceive yourself to be is an illusion produced by atoms bumping together in your skull. In this view, “you” don’t actually exist at all. There is no “you”, there’s just a pile of atoms bumping into each other.
In this view, your mind and consciousness are being caused by the material world, meaning it is entirely the result of physical interactions and the random decay of subatomic particles. Your brain causes all your thoughts and decisions. And you don’t have any control over it because it’s all been predetermined by arbitrary laws of physics.
The alternative is that consciousness and mental states somehow transcend the material world and could conceivably exist independently of it. Of course, this would be perfectly consistent with belief in God as just such an immaterial supernatural mind.
Maybe you think the physical world is all that exists, but that view is incompatible with the existence of genuine thoughts and choices. If you believe you exist and that your own mind is real, you should probably believe in God.
(I didn’t come up with these arguments, but they’re so common that they can be considered common knowledge in apologetics circles. I’m citing no sources for the scientific claims because they’re also pretty well established. Feel free to Google them).