![]() This doesn't mean we can reach everything in the part of the Universe we can see! The most distant parts of the Universe are only visible during the earliest stages. Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL / E. However, we can still see the galaxies beyond that, except we're limited to seeing them as they were in the past. Galaxies more than about a third of the way to the boundary of what we can observe can never be reached due to the Universe's expansion, leaving only 3% of the Universe's volume open to human exploration. Within the observable Universe (yellow circle), there are approximately 2 trillion galaxies. In fact, we can see objects that are farther away than 13.8 billion light-years today, all because of the fact that the fabric of the Universe itself is expanding. That galaxy might be 13.8 billion light-years away right now, but the light didn't need to travel for 13.8 billion years to reach us it traveled a shorter distance and for a shorter amount of time. When they first emitted the light that's reaching us today, this occurred at a time that was already billions of years ago. The objects that are 13.8 billion light-years away from us now were much closer in the distant past. Today, there's light arriving at our eyes from all sorts of different objects at all sorts of different distances. This affects all forms of radiation, including the leftover glow from the Big Bang. space between ourselves and the galaxy redshifts the light on its journey from that distant point to our eyes. It isn't simply that galaxies are moving away from us that causes a redshift, but rather that the. It's the matter and energy density of the Universe that determines how quickly the Universe expands, and we have to add up all the different types of energy, including neutrinos, radiation, dark matter and dark energy, to get the right answer. This is why we talk about the redshift of distant objects: because their light gets stretched as the fabric of the Universe expands. Instead, what's happening is that the fabric of spacetime itself is expanding, and the light coming from these objects is getting stretched - to longer, redder wavelengths - as the Universe expands. In reality, the objects themselves aren't moving, just like the raisins aren't moving relative to the dough that they're in. Ned Wright, based on the latest data from Betoule et al.īut I keep saying something you may be glossing over: it appears that these objects move away from us at these speeds. Note how these lines are all different from one another, as they correspond to Universes made of different ingredients. The data strongly favors an accelerating Universe. The distance/redshift relation, including the most distant objects of all, seen from their type Ia. It's not a speed it's a speed-per-unit-distance. The reason is because the expansion of the Universe depends on how far away an object is from you. A light signal sent from it to you would take a very long time to get there. But if you were to look at a raisin that was much farther away, it would appear to recede much more quickly. If you were to look at a raisin that's close by you, it would appear to move away from you relatively slowly, and a light signal sent from it to you would only take a short amount of time to get there. The Universe doesn't expand at the speed of light, the speed of sound, or any other speed. The expansion of the Universe isn't about a speed. This is the key point that's so hard for most people to understand. In reality, it's the space between them that's expanding. This can be very confusing if you insist on attributing the apparent motion of the objects we see to their relative velocities through space. ![]() ![]() ![]() but the distances between them do in an expanding Universe. The individual structures (coins) don't expand. The balloon/coin analogy of the expanding Universe.
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