How to show google.com in an iframe?

The reason for this is, that Google is sending an "X-Frame-Options: SAMEORIGIN" response header. This option prevents the browser from displaying iFrames that are not hosted on the same domain as the parent page.

See: Mozilla Developer Network - The X-Frame-Options response header

IT IS NOT IMPOSSIBLE.
Use a reverse proxy server to handle the Different-Origin-Problem. I used to using Nginx with proxy_pass to change the url of page. you can have a try.

Another way is to write a simple proxy page runs on server by yourself, just request from Google and output the result to the client.