While the use of scientific notation expands the range of numbers we can represent with fixed-size chunks of data, it still doesn't cover arbitrarily large numbers.
Some numbers are just too big to fit into a fixed-size number representation.
For example, can't be represented, because the exponent 500 won't fit into two digits, and the mantissa is as large as it can be. Numbers that are too large for our representation schema can arise during a computation. When overflow occurs, some language implementations signal an error and stop the computation. Others designate some symbol, called infinity, for all numbers that are too large. Arithmetic operations are aware of infinity and propagate it.