On the internet it’s very useful to quickly tell whether someone is asking questions about Christianity in good faith or just trying to waste your time. There are lots of ways, I’m going to show one easy one.
It’s this: Point out that the existence of gravity cannot be empirically verified, it can only be shown through its effects. Then see what they do.
Now, this is unarguably true. Something which can be empirically verified is something which can be directly observed by the senses (possibly with the aid of an instrument, such as a magnifying glass or stethoscope). Gravity:
- Has no color and cannot be seen*.
- Has no taste.
- Has no smell.
- Does not feel like anything. (if you push on it, there’s no resistance. Your arm might feel heavy, but the gravity itself doesn’t feel like anything.)
- Has no sound.
It is easy to discover that there is gravity, though the difficulty depends on exactly what you mean by gravity (gravity as described by general relativity is hard to discover), but it must be done by observing the effect of gravity upon things. After observing this effect one can then infer the existence of gravity, but the gravity itself cannot be observed.
Gravity is, in this regard, like observing wind purely by sight. You cannot see the wind, you can only see the effect of the wind.
This is not a controversial point, and it’s not a difficult point. If you can empirically observe something you can say what color it is, how loud it is, what it tastes like, what it smells like, or what it feels like. You can do none of these things with gravity. This is what makes it a useful test.
If an atheist acknowledges this point (and proceeds in a manner consistent with acknowledging this point), he’s probably sincere and not merely trying to waste your time. If he twists himself up into self-contradictory knots trying to fight this point, he’s just trying to waste your time.
The only reason anyone ever has for denying something which is obviously true is because their primary goal is not the truth.
*This is not quite 100% true as one can argue that gravitational lensing is actually directly observing gravity. The only problem with this is that no one has actually seen gravitational lensing. It has been observed in radio frequencies by radio telescopes, but humans do not see in radio frequencies. Once you have an instrument which translates what we cannot see (etc) to something that we can, you have to make arguments for why the translation is correct, and those arguments cannot be empirically verified. Thus anything which rests upon observations through translating equipment is not empirically verified by rests upon indirect observation and argument.