I've had a website on my own domain for quite a while now, but I recently acquired a new domain name. With the new domain, I want the main page to be identical to my existing site, so that the stories I post can be seen on either URL and the user can pick whichever URL they prefer to see the site.

The problem is I'm pretty sure there's no way to do this without getting penalized for having duplicate content. I don't want to redirect since I would like the user to be able to use either URL.

Is there any way to do this without getting penalized? Maybe loading the first domain in a frame in the second domain? Though I don't really like that option.

Maybe you can use the robots.txt to limit bots access to one domain

I think you ought to move the domain to either one. Having two domains also splits PageRank, doesn't it?

If it were just two subdomains, it might be less of an issue, after all many sites have a duplicate www and non-www version. But two domains might be different.

Yeah, I was afraid of that...I could use the robots.txt to not index one of the domains (if that would work), but then I wouldn't get additional pagerank if the wrong domain was linked.