# No-cloning theorem and time travel

• stevenytc
In summary: Therefore, the possibility of time travel and cloning would violate this assumption. In summary, the no-cloning theorem contradicts with the possibility of time travelling due to the violation of unitary evolution.
stevenytc
Does no-cloning theorem contradict with the possibility of time travelling?

If i send a photon back in time from t1 to t0, then between t0 an t1, I could have two identical photons, in other words, i can use the time machine to clone my photons.

Have I missed out something?

stevenytc said:
Does no-cloning theorem contradict with the possibility of time travelling?

If i send a photon back in time from t1 to t0, then between t0 an t1, I could have two identical photons, in other words, i can use the time machine to clone my photons.

Have I missed out something?

Time machine? Really?

stevenytc said:
Does no-cloning theorem contradict with the possibility of time travelling?

If i send a photon back in time from t1 to t0, then between t0 an t1, I could have two identical photons, in other words, i can use the time machine to clone my photons.

Have I missed out something?
Your procedure violates unitary evolution. The no-cloning theorem assumes that evolution is unitary.

Demystifier,

Thanks for your response.

But could you elaborate on exactly how this operation violates the unitary assumption?

Thanks.

Unitary evolution involves an evolution from t0 to t1, but not an independent evolution from t1 to t0.

## 1. What is the No-cloning theorem?

The No-cloning theorem is a fundamental principle in quantum mechanics that states it is impossible to create an exact copy of an unknown quantum state. This means that it is not possible to perfectly replicate a quantum system without prior knowledge of its state.

## 2. How does the No-cloning theorem relate to time travel?

The No-cloning theorem has implications for time travel because it suggests that it is not possible to travel back in time and create an exact copy of something that already exists in the past. This is because the state of the quantum system would have already been observed and cannot be perfectly replicated.

## 3. Can the No-cloning theorem be violated?

No, the No-cloning theorem is a fundamental principle of quantum mechanics and has been proven mathematically. It is a necessary consequence of the uncertainty principle and cannot be violated.

## 4. Does the No-cloning theorem apply to classical systems?

No, the No-cloning theorem only applies to quantum systems. Classical systems are deterministic and their states can be perfectly measured and replicated.

## 5. Are there any exceptions to the No-cloning theorem?

While the No-cloning theorem holds true for unknown quantum states, there are some exceptions for known states. For example, it is possible to create an exact copy of a qubit (a quantum bit) if its state is already known. Additionally, approximate cloning is possible for certain quantum states, but it is not an exact replication.

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