Observation and knowledge of reality are topics that raise all sorts of prickly philosophical questions, chief among them the one that asks if a tree falling in a forest with no one to hear it makes a sound.
You're as likely to reach consensus on that question as you are on whether the chicken came before the egg.
But I've got another, more modern one for you; if a terrorist act happens on the other side of the world and you don't know about it, did it happen?
The answer to that one is, quite simply, "yes".
Or is it?
If you're inclined to see yourself as the centre of your own universe (which, if we're honest, we mostly all do), it's easy to entertain the idea that only the things we know about and perceive can exist.
Subjective idealism is a selfish, narrow way to live in the world, but as the world increasingly seems to be such a worrisome one, is that such a bad thing?
This week as I drove to work humming away happily in my small-town, bottom-of-the-world bubble thinking about the day ahead, I switched on the radio to listen to the news headlines.
Every single item was about the wholesale murder of innocent people at the hands of terrorists in different but equally far-flung countries around the world. As I imagined the death of young children, the suffering of the injured, the grief of those left behind, I felt as if a dark cloud had been drawn across my previously sunny day.
I went from happy to sad in the space of a news bulletin and stayed that way until real life took over and I got absorbed in the here-and-now.
While the journalist in me will always believe passionately in the power of news to inform and then transform, the mother and provincial New Zealander in me was selfishly wondering if I would have been better keeping the radio off.
What purpose was served by my knowing of the tragedies being faced by those far from me, unless I was willing and able to do something about them?
To paraphrase Stephen R. Covey's first habit from the widely read 7 Habits of Highly Effective People, international terrorist acts were outside my circle of influence, and should therefore be outside my circle of concern.
Either I took some action to influence change in this area (and let's face it, even the world superpowers are struggling to do this), or I didn't bother myself with what was going on.
This sort of head-in-the-sand attitude doesn't generate friends, but it also avoids feeling hopeless, helpless and afraid, as the world seems to spiral further out of control.
Earth has always been a brutal and unfair place. But is it any more so lately? Or are we just more easily able to tap into global misery as it streams live and unfiltered to the phones we all carry in our back pocket?
Recently, my die-hard habit of watching the 6 o'clock TV news has fallen away, mostly just because it's the witching hour for parents and my focus is on mashed potato and gravy instead. The time I once had for being a news consumer has diminished and I've got caught up in my own world instead of the worries of the wider one.
On occasion I've felt bad about this, but mostly I've just felt happier.
Maybe one day I'll be in a better position to change the world, but until then, I can't help thinking that the oft-quoted line "sit down and shut up" might not be better said as "stand up or shut up" and " ultimately " switch off.
- Eva Bradley is a columnist and photographer.