Astronomers can observe objects in the universe that are as old as 13.3 billion years because of the way light travels through the expanding universe. While it's true that the universe is approximately 13.7 billion years old and that the expansion of spacetime affects the distance that light can travel, it does not limit our observations to a maximum of 6.85 billion light years.
When we look at distant objects in space, we are essentially looking back in time because light takes time to reach us. The speed of light is indeed a cosmic speed limit, but the expansion of the universe does not violate this limit. It's important to note that the expansion of space itself is not constrained by the speed of light; it's the motion of matter and information within space that is limited by the speed of light.
As space expands, it stretches the wavelengths of light traveling through it, a phenomenon known as cosmological redshift. This means that light from distant objects is shifted towards longer wavelengths, making it appear redder. By measuring this redshift, astronomers can determine how much the universe has expanded since the light was emitted.
To see objects that are 13.3 billion light-years away, astronomers observe the light that has been traveling towards us for 13.3 billion years, taking into account the redshift caused by the expansion of the universe. The light has had enough time to reach us despite the expansion because the expansion rate of the universe has not always been accelerating. In the early universe, the expansion was slower, allowing light to travel across greater distances.
While there are regions of the universe that are currently beyond our observational reach due to the accelerated expansion, we can still observe light from objects that were much farther away at earlier times. By studying the light from these distant objects, astronomers gain insights into the early universe and its evolution over time.