How do we know that time exists?
This is a complex question.
First, we cannot make sense of a question like this without first establishing what we mean by knowledge.
For convenience, let's pick the popular justified true belief (JTB) definition of knowledge. On this definition, the following conditions must be met in order for us to know that time exists:
- It has to be true that (some kind of) time in fact exists (for sake of argument, let's grant that this is the case)
- We must believe this is the case (pretty much everyone does, so let's grant this as well)
- We need to be aware of a justification for our belief in the proposition that time exists
And here lies the heart of my question: What justification do we have to believe that (some kind of) time exists?
One possible attempt at justification would be to appeal to our subjective personal experience of time (e.g. "I know that time exists because I have the subjective experience of perceiving things changing over time"), but then this kind of justification would be vulnerable to proving too much, since people could just as easily use the same justification to justify other controversial beliefs, such as:
- Belief in ghosts, angels, demons, etc. (e.g. person X says "I know that ghosts exist because I have personally experienced/witnessed ghosts")
- Belief in aliens (e.g. "I know that aliens exist because I have subjectively experienced aliens (I was abducted by aliens)")
- Belief in past lives (e.g. "I have subjectively experienced visions of my past lives")
- Belief in some specific religion (e.g. Mormons for example appeal to the witness of the Holy Ghost; William Lane Craig also makes a similar argument here)
How can we justify our belief in the existence of (some kind of) time without "proving too much"?
Or should we just bite the bullet?
Regarding justification, this is probably related: Is there an objective standard of sufficient evidence?