Yes, we can look back in time using optical telescopes and radio waves. When we observe distant objects in space, we are essentially observing them as they were in the past because it takes time for the light or radio waves they emit to reach us.
In the case of optical telescopes, they capture and detect visible light from celestial objects. The light emitted by these objects travels through space at a finite speed, which is approximately 299,792 kilometers per second (or about 186,282 miles per second) in a vacuum. This means that the light we receive from distant objects has taken a certain amount of time to reach us. For example, if we observe a star that is 1,000 light-years away, we are seeing the star as it appeared 1,000 years ago because the light we receive today left the star 1,000 years ago.
Similarly, radio waves can also be used to observe celestial objects. Radio telescopes capture and detect radio waves emitted by astronomical sources. Like light, radio waves also travel at a finite speed. By analyzing the radio waves received from distant objects, we can study them as they were when the waves were emitted. This allows us to look back in time and study the early universe, distant galaxies, and other astronomical phenomena.
So, whether we use optical telescopes or radio telescopes, we are effectively observing the universe as it appeared in the past due to the finite speed of light and radio waves. The farther away an object is, the further back in time we are observing it.