Happening or existing or done at the same time

Usage examples of simultaneity.

That meant he had left Mars three hundred and fourteen years ago by Old Earth time, three hundred and thirty-eight years ago by Dest time, ignoring, as he always did, the fact that it was virtually meaningless to speak of simultaneity on two planets so far apart in a relativistic universe.

Simultaneity and interactivity - this will be the name of the game in the Internet.

On six levels of this hostelry holovision sets give forth their offerings with numbing simultaneity.

Speed, velocity, simultaneity, acceleration, and other mathematical abstractions having to do with the pattern of eternity were part of Martian mathematics, but not of Martian emotion, Contrariwise, the unceasing rush and turmoil of human existence came not from mathematical necessities of time but from the frantic urgency implicit in human sexual bipolarity.

This simultaneity and concurrency are central tenets of imposing Shock and Awe.

Simultaneity is an illusion, friend, when you are juggling and even when you are not.

Now, driven by a new urgency (and augmented by virtually the entire population of the Walled City, working in a mode of simultaneity that very nearly approximates unison) he succeeds in actually being there, within a space defined by the emerging factors of the nodal point.

By this measure, quantum mechanics and the theories of relativity are deep beyond anyone's wildest expectations: Wave functions, probabilities, quantum tunneling, the ceaseless roiling energy fluctuations of the vacuum, the smearing together of space and time, the relative nature of simultaneity, the warping of the spacetime fabric, black holes, the big bang.

Establishing absolute simultaneity without a privileged frame would require an infinitely fast synchronizing signal, which SRT says we don't have.

But I know what you mean when you say the Theory of Simultaneity, in the way I know what is meant by the Theory of Relativity.