Yes...it also violates the law of conservation of energy. Probably THE biggest law that can be violated.
Let's say I have a time machine and 'go back in time'. Well, that causes mass/energy to disappear from now....which itself violates the law....and to re-appear in the past...which again violates the law. I mean, my time machine just appearing out of nowhere is effectively the creation of new mass/energy from nothing, in the past. And it gets worse...as the atoms my time machine is made of would actually already exist back then, so I'd be violating various quantum laws regarding quantum states and cloning.
That's what all backward time travel plots forget. Whatever you are taking back in time already exists ( in some form ) back then. You are thus creating the grievous scientific crime of duplicating atoms in the past.
But also the time jump itself causes the same energy from the future to cease to exist in the future and thus preserving the overall conservation of energy in the totality of spacetime --
if T-symmetry is indeed postulated. However, T-symmetry remains a highly disputed postulation amongst theoretical physicists as there remain strong grounds to postulate the arrow of time.
Causality, however, is a whole other kettle of fish. Many a philosophically untrained theoretical physicist and their avid followers/listeners have incorrectly hijacked this far broader and more fundamental philosophical notion (causality = a thing -- whether entity, property or behaviour -- having a cause) to mean that
a cause precedes the effect in time whereby causality is inextricably bound by time. And yet even within physics there are causes of behaviours, properties and entities that happen simultaneously with the effect where invoking any notion of time is meaningless.
To hark back on this thread to John Wheeler's encapsulation of Einstein's relativity:
'Spacetime tells matter how to move; matter tells spacetime how to curve.'
More precisely, in relativity spacetime
causes matter to move along certain pathways whilst matter somehow
causes spacetime to curve. Whatever be the best formulation of this principle, anything
causing spacetime to curve is by logical necessity meta-spatiotemporal and perfectly instantaneous rather than time-bound. In other words, matter causes
time itself to behave in a certain way and therefore demonstrates a causality that necessarily occurs outside/beyond time and refutes the more limited definition of causality as being something necessarily time-bound.
Similarly, other physical laws -- such as the second law of thermodynamics whereby
the entropy of isolated systems is bound to increase (receiving no harnessed energy from outside the system to decrease entropy) -- is by necessity meta-spatiotemporal. All of the universe seems to follow this principle based on all observations leading us to conclude, in causal terminology, that such a law
causes certain behaviours instantly and simultaneously with the cause rather than the effect following the cause in time. Similarly, few would dispute that the sun is the cause of its radiation. And yet there's no way of clearly determining whether sun
precedes in time the point at which it first generates radiation. And so on and so forth. Physics is full of what's called 'essential causality' in philosophical ontologies as opposed to studying merely 'causalities of time'.
Leibniz's
Principle of Sufficient Reason (i.e. everything has a cause / sufficient reason) is perhaps the most famous articulation of causality and in many ways most working scientists, irrespective of discipline, assume it (wittingly or unwittingly) as a basis of their work. That is to say, they consider their main objective as scientists to be a quest for observer-independent (objective, realist) explanations to observed phenomena by trying to answer the question 'What causes this observed behaviour / entity / property?' PoSR is philosophically deliberately non-specific as to the
type of reasons or causes implied -- say, time-bound causes or non-time-bound causes. In other words,
any entity, property or behaviour can theoretically have (1) both
deterministic or
indeterministic causes ('law-likeness' vs. 'chanciness'). The entity, or its property or behaviour, may have (2) causes both/either
within the entity (self-caused) or
outside the entity (other-caused). And yet (3) causes may be
total causes (causes for the very existence of an entity) or
partial causes (causes for a particular property or behaviour of an entity). And yet furthermore, and closely related, (4) causes may be
composite (many causes) or
simple (single cause). Even the foregoing list of four types of causes is not exhaustive in terms of all logically possible types of causes.
All of the above types of causes are worth exploring in any exercise purporting to describe itself as 'scientific', not just causalities of time. What PoSR squarely disagrees with is the philosophical alternative that an entity, property or a behaviour can be/occur
without any cause whatsoever. This fundamental rule posited by the PoSR is often justified by appeal to the philosophical dictum
ex nihilo nihil fit ("nothing comes out of nothing").
According to the dictum, while it's logically possible that there be an entity or a property that has no cause whatsoever, it's an absurd and unhelpful possibility. Hence, for instance, the known universe may be, under the PoSR, rationally explored
either as having a sufficient reason
within itself for its own existence (self-caused) or
without itself (other-caused). But the third option that there is
no sufficient reason for the universe to exist is regarded as absurd, for the question can always be reasonably asked: If the universe does not have a sufficient reason to exist at all, how come it exists nonetheless? The proponents of the third option forbid the question 'why' or 'how' and insist on acceptance of its existence as a brute fact.
Footnote: Philosophically the question 'what causes time?' (irrespective of whether time has an infinite past or not) is perfectly reasonable and hence the simplistic and popular physicalist understanding that causality logically necessitates a cause-and-effect relation
in time is both incorrect and superficial. Hence, a self-caused universe that has always existed is a perfectly logical statement when understood in terms of 'the universe containing within itself a sufficient reason for its own existence'. Similarly 'a universe that has always existed may have a sufficient reason for its existence outside of itself' is also perfectly logical. The key takeaway here, however, is that this dilemma is a metaphysical (philosophical) one and hence
unresolvable scientifically. Any effort to do the latter stumbles upon a category mistake.