How do scientists know that dark matter and dark energy exist even if we can not see them

Dark matter has been given this name because it doesn't seem to interact with regular matter in any way. It doesn't collide with it, or absorb energy from it. We can't see it or detect it with any of our instruments. We only know it's there because we can see the effect of its gravity.

how did justinian contribute to the byzantine empire?

one famous byzantine emperor was justinian i. justinian ruled from ad 527 to 565. belisarius was the commander who led these armies in an attempt to win back the old western roman empire. the war effort to take back the western part of the empire forced justinian to raise taxes on the people of the byzantine empire.

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