To watch the signing of the Declaration of Independence live, you don't need a time machine. You just need a telescope and a way to catch up to the light that left Earth in 1776.
Because of the cosmic speed limit of light, it is physically impossible to look at the universe without looking backward in time. Whenever you look at the Moon, you are not seeing it as it is right now; you are seeing it as it was 1.3 seconds ago. The light from the Sun takes eight minutes to reach Earth, meaning if the Sun were to suddenly vanish, the sky would remain bright for exactly eight minutes before going dark. The farther out you look, the deeper into history you peer. The Andromeda galaxy is 2.5 million light-years away. If an observer standing on a planet in Andromeda today aimed a miraculously powerful telescope at Earth, they would not see modern human civilization. They would see early hominids roaming the African savanna.
Astronomers use this exact phenomenon to study the infancy of the universe. By pointing telescopes at seemingly empty patches of sky for days at a time, they capture light that has been traveling for billions of years, literally photographing the past.
The catch is that catching up to that old light is effectively impossible under current physics. Because the light from 1776 is currently expanding outward about 250 light-years away, you would have to travel faster than the speed of light to overtake it. Under Einstein’s theory of general relativity, no object with mass can accelerate to or exceed the speed of light in local space.
The only mathematically permissible loophole is folding spacetime itself, a concept known as an Einstein-Rosen bridge or a wormhole. Instead of traveling through space faster than light, a wormhole connects two distant points directly. If a traveler stepped through a theoretical wormhole that opened 1,000 light-years away from Earth, they would beat the light there. By turning a massive telescope back toward Earth, they could watch the Middle Ages unfold in real time. However, keeping a wormhole open requires exotic matter with negative energy density—a theoretical substance that has never been observed and likely cannot exist outside of mathematical equations.