I weigh 140lbs and when I go touring I don't carry more than 50lbs. Does this mean that this is equivalent to a 190lb person riding the bike with no gear.

In terms of wear and tear on the bike's parts? Yes, generally speaking.

WW77, No. The weight distribution will be different. Also, possibly, musculature.

What about a single-wheel trailer...?

Is it worse on your bike than panniers or better?

All other things being equal, a 190-pound person would probably produce more power. It's the power-to-weight ratio that's important. Of course this wouldn't apply if that extra 50 pounds were all fat.

When you go over a bump, you can absorb some of the shock to your bike by standing up and flexing your knees and elbows. You can't absorb the shock from gear weight. Also, gear on racks sits out to the side, so gear weight creates a larger lateral stress on your frame and wheels.

Generally speaking 50 lbs of gear is harder on a bike than 50 lbs of rider, but it's tough to quantify it.

Even if the extra 50 lbs is fat, the 190-lb person is used to carrying it around, and you're not. Still, it's comparing apples and oranges, trying to get a fat fit rider for comparison, etc.

I'd think it's more about proportions. For example, I'm 200 lbs, and I've carried 50 lbs on tour. A 100 lb person carrying the same weight would be more impressive. I would be pedaling 1.25 Neilfeins around, but the toothpick is pushing half again of his weight up those hills.

Out of curiosity, who do you ask?