Question: When I consider my own existence with respect to time I can imagine three possibilities: 

(1) **Time extends infinitely into the past.** In this case, how can the present, with me in it, exist, since there would be an infinite period of time that existed before the present. That seems illogical. 

(2) **Time had a starting point from which everything in our universe evolved to the present (t=1).** That possibility would require something (God) to start the clock ticking (t=0). But in this case we're back to square 1 with the problem of an infinite past. So the only possibility that makes sense to me is a third possibility 

(3) **Where time is some sort of abstraction in human consciousness that we need in order to relate cause and effect.**

Answer: 
I will attempt to present the stance of physicist [Julian Barbour](https://en.wikipedia.org/wiki/Julian_Barbour), who presented a compelling answer to this question in a lecture I saw him give in Oxford ([this lecture](https://www.youtube.com/watch?v=I5rExaKLEoU)). 

He is firmly *not* in the camp of the latter viewpoint in your title, but I wouldn't necessarily put him in the former camp either. He puts his view of time in terms of the [primary/secondary quality distinction](https://en.wikipedia.org/wiki/Primary/secondary_quality_distinction) and refers to Galileo, who in 1623 classified attributes such as color and sound as secondary characteristics of matter that are perceiver-dependent. Rather than photons entering eyes or vibrations entering ears, in the case of time we have our perception of the *successiveness* of events streaming through the system we know as consciousness. These progressions correspond with an increase in system complexity, with all consciousnesses experiencing a flow of time along a line of increasing complexity.

All in all a fascinating viewpoint that I've hardly done justice here. After the lecture, he recommended that people watch [this video](https://www.youtube.com/watch?v=WKsNraFxPwk) for a more in-depth look (assuming they didn't want to read *[The End of Time](https://en.wikipedia.org/wiki/The_End_of_Time_%28book%29)* or any of his papers) so I will pass that along as well. 

Lastly, I'll add something because it made me laugh and because it is bound to come up if you consider the implications of this position: When someone asked him what all this means about free will, he said “I'm not sure it matters much. It *feels* free anyway, and I'm excited to find out what I'll do next.”
3 is correct. Time is a abstraction, a filing system used to arrange events and memories into a logical system of cause and effect.

Per relativity, space and time are not discrete entities, but a single construct called spacetime. Saying something is X km long is equal to saying it is Y seconds long. All units of time are based on and can be reduced to measures of distance.

Time is a mental construct used to make sense of movement. Movement produces the sensation and experience of time, not the other way around.