Science is based upon a process known as the Scientific Method. All science uses a modified form of this.
- Obersvation / Question - the scientist observes (notices) something s/he wants to learn more about, or comes up with a question he wants answered. For example, it rains on cloudy days. Why does it rain on cloudy days?
- Hypothesis - a guess as to the reason behind what he observes. The clouds are made of Super Crows, and when they shit it rains.
- Prediction - subtly different from hypothesis, it is the testable results expected if your hypothesis is true. If I look at a cloud with a telescope, I should be able to see the Super Crows.
- Experiment - carrying out the test implied by your predictions
- Conclusion - assessing whether you were right, how good the experiment was, etc. I didn't see any Super Crows, but I accidentally left the cap on the telescope, so I think that's why, and I need to try again.
You'll note that the key to this whole process is the ability to perform a test, experiment, or observation that can verify or deny your hypothesis. Some things are impossible to test, or impossible to prove false. There is a pink elephant somewhere on Earth. It's really damned hard to go everywhere on the Earth, and even if you could and you missed him, maybe he snuck to Nepal while you were in Japan, and then snuck back to Japan when you left for Antarctica. Johnny's got a crush on Melissa. You ask him if he's got a crush on her. If he says yes, you've proven your hypothesis true. If he says no, he's in denial to himself, or isn't admitting it to you, proving your hypothesis true. It's impossible to prove your hypothesis false.
Either of these cases are unfalsifiable - impossible to prove false through an experiment. A whole class of things that fall under "unfalsifiable" are the supernatural, including any higher powers and their effects, such as God, Creationism, and Intelligent Design (ID). I'm not saying ID is wrong, I'm saying it's untestable. There is nothing we can do to determine whether God created Adam and Eve, or just helped evolution along, or even only started the ball rolling with the Big Bang and then took a seat in the sidelines (sometimes called the Clockmaker Hypothesis).
- Science requires the process of testing.
- ID is impossible to test.
- Logical conclusion: ID has no place in science.
Once again, just to make sure you get it, science does not say Intelligent Design is wrong, science says it is unable to say anything about it. Science admits a total failure to address the issue of God, and leaves it to the churches, the atheists, and the ACLU to duke out.