I have the following question from Computational Complexity - A modern Approach by Sanjeev Arora and Boaz Barak:
Prove the existence of a universal TM for space bounded computation (analogously to the deterministic universal TM of Theorem 1.9).
That is, prove that there exists a Turing Machine $SU$ such that for every string $\alpha$ and input $x$, if the TM $M_\alpha$ -- the TM represented by $\alpha$ -- halts on $x$ before using $t$ cells of its work tape, then $SU(\alpha, t, x) = M_\alpha(x)$ and moreover, $SU$ uses at most $C\cdot t$ cells of its work tape, where $C$ is a constant depending only on $M_\alpha$.
After checking theorem 1.9 and the universal TM with time bound, I see that the construct $SU(\alpha, t, x)$ means that the Turing machine SU stops after $t$ steps. However if this is the case, then it means that we can create a Turing Machine equivalent to $M_\alpha$ such that the new Turing Machine stops in $t$ steps where $t$ is the "space" used in the original.
However, this seems a dubious interchange of space and time. If on the other hand, $t$ actually meant that the second machine stops within $t$ space, too, then the second part does not make sense any more because it says $SU$ uses $Ct$ cells, which is not $t$.
So my question is how do I interpret this? Is the first interpretation really possible?