The major reason why blues and other whales can get so big has nothing to do with their diet. It is that water supports their weight, so their skeleton doesn't have to.
The weight of an animal goes up with its volume, which is measured in meters cubed, while the strength of its bones goes up (roughly speaking) with its cross section, which is measured in meters squared. As an animal gets bigger and bigger, the bones required to support its weight must get bigger, faster, until eventually the animal reaches a practical size limit, where as much of it is bone as possible (and it is virtually a stationary tower.) (And that, by the way, is why you cannot have an ant the size of a skyscraper, 50's horror movies aside. If you just scaled up the ant, the weight would go up faster than its structural strength. A skyscraper ant would collapse on its belly, immobile.)
But with whales and other creatures whose weight is supported by water, the limit is set by availability of food, and that is a very high limit. I imagine even larger animals than blue whales could evolve, eventually.
Incidentally, that is also why bigger dirigibles are more cost-effective than small ones. You can double the fabric in a dirigible, and get much more than double the lifting power.
The major reason why blues and other whales can get so big has nothing to do with their diet. It is that water supports their weight, so their skeleton doesn't have to.
The weight of an animal goes up with its volume, which is measured in meters cubed, while the strength of its bones goes up (roughly speaking) with its cross section, which is measured in meters squared. As an animal gets bigger and bigger, the bones required to support its weight must get bigger, faster, until eventually the animal reaches a practical size limit, where as much of it is bone as possible (and it is virtually a stationary tower.) (And that, by the way, is why you cannot have an ant the size of a skyscraper, 50's horror movies aside. If you just scaled up the ant, the weight would go up faster than its structural strength. A skyscraper ant would collapse on its belly, immobile.)
But with whales and other creatures whose weight is supported by water, the limit is set by availability of food, and that is a very high limit. I imagine even larger animals than blue whales could evolve, eventually.
Incidentally, that is also why bigger dirigibles are more cost-effective than small ones. You can double the fabric in a dirigible, and get much more than double the lifting power.