Is quantum field theory the return of the ether?

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Quantum field theory (QFT) is often compared to the concept of ether, but it fundamentally differs in its treatment of spacetime and relativity. QFT utilizes quantum fields that are relativistically covariant, meaning they adhere to the principles of relativity and are consistent across different observers. The vacuum state in QFT can be viewed as a relativistic aether, where light waves are excitations of this vacuum. However, unlike the classical ether, the vacuum state remains invariant for all observers moving at constant velocity. Therefore, while there are similarities, calling QFT a reinvention of the ether is misleading.
lucid
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Hi,

My question is about why quantum fields are used.

Are quantum fields just a reinvention of the ether? It seems like something superimposed on spacetime (from which theoretically spacetime should emerge in the case of gravity) from which particles can pop in and out of.

How wrong is it to call quantum field theory a reinvention of the ether?
 
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no. quantum fields are manifestly relativistically covariant, since they belong to a certain representation of the Lorentz group by construction.
 
Quantum fields can be said to have a relativistic aether (the "vacuum state") - in the sense that light waves are excitations of the vacuum state. However the vacuum state is the same for all observers moving at constant velocity, and in this way it is different from the non-relativistic aether.
 

Thread 'Two equivalent statements of time reversal symmetric Hamiltonian'

Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?
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