command substition for multiline output of command?

How can I make the following command substitution work?

$ time

real    0m0.000s
user    0m0.000s
sys 0m0.000s

$ oldtime="$(time)"
bash: command substitution: line 23: syntax error near unexpected token `)'
bash: command substitution: line 23: `time)"'

I guess it doesn't work because the output of the command has multiple lines, because one line output works:

$ oldtime="$(echo hello)"
$ echo $oldtime
hello