There are more than 600 million websites on the Internet, according to the tech site Pingdom.

That includes about 18 billion Tumblr blogs, 36 billion photos uploaded to Facebook each year, an average of 175 million tweets a day and 144 billion emails sent a day.

And the internet keeps growing. But is there limit to the internet’s size? Markus Hoffman, head of Bell Labs Research in Holmdel, New Jersey, says yes — and we're approaching it.