Physicists are now saying that spacetime is emergent. Theoretical physicist Sean Carroll has already authored and published a book: ‘Something deeply hidden: quantum worlds and the emergence of spacetime’.
But, do these physicists actually know what emergent spacetime signifies? Perhaps they will be shocked and embarrassed if they come to know that this signifies that there is something eternal and everlasting in nature.
Any change can occur either in space or in time. A hot cup of tea being at the same place on a table may become less hot with the passage of time. This is one sort of change. The teacup may be removed from the table after it has become empty. This is another sort of change. In one sort of change, the teacup is moved through space from one place to another place. In the other sort of change, the teacup is not moved through space, but its overall physical state changes from its earlier state. In both cases, both space and time are required for such changes to occur.
Therefore, if something is not within any space and time, then no change can occur in it. It cannot move through space from one place to another, because there is no space outside it. Its overall physical state cannot alter with time, because no clock ticks outside it. So, it will remain the same forever. And thus, it will be eternal and everlasting. This is nothing but simple logic.
Emergent spacetime implies one more thing: multiverse is impossible. Spacetime is emergent means the source from which spacetime has emerged cannot be within any spacetime, because there cannot be any spacetime prior to its emergence. Something is not within any spacetime means there is no spacetime outside it. As there is no spacetime outside it, so there cannot be anything outside it, because for anything to exist outside it spacetime is required. So, neither can there be any other universe outside it.
Scientist Hyun Seok Yang has shown in a paper that in case of emergent spacetime there will be inflation, but there will be no eternal inflation. Inflation will stop after generating only one universe. So, in case of emergent spacetime, there will be no multiverse.
By logic alone we have also arrived at the same conclusion that in case of emergent spacetime there will be no multiverse.
Wave-function of the universe also shows multiverse is impossible. Everybody knows wave-function equation of the universe does not contain any time-factor, which means it is not possible for us to know how the wave-function of the universe is changing with time. As the wave-function of the universe always remains the same, so that will mean the universe also always remains the same; it does not change with time.
But how is this possible? This is because we know very well that change is always taking place within the universe. So, how can it be that the universe as a whole always remains the same?
But changes within the universe do not mean that the universe as a whole is also undergoing change. If we want to measure how the universe is changing as a whole, then we will have to place the entire universe in some space-time frame that will have to be outside the universe. This space-time frame cannot be within the universe, because we want to place the entire universe in that frame. Then with respect to a clock running in the outer space of the universe we will have to find out which state the universe was in at an earlier moment and which state it is in at present. These data will then give us the necessary information for evaluating how much change has occurred in the universe as a whole. However, if there is no spacetime outside the universe, that is, if no clock is running in the outer space of the universe, then neither will there be any earlier moment for the universe nor will there be any later moment. And the universe will be in a timeless state, unchanged forever.
As the wave-function of the universe does not contain any time-factor, so on the basis of the above analysis we can say that this wave-function indicates that there is no spacetime outside the universe, which will further mean multiverse is impossible.