Are they talking about the observable universe or the unobservable universe? [closed]

Question

When people say that 95% of the universe is dark matter and dark energy, are they talking about it being in the observable universe or the unobservable universe?

Because surely all matter in the universe must have a gravitational pull because it has mass, just because we dont see it anymore doesn't mean it's force has disappeared from the observable universe?

So what if the matter we can't see outside the observable universe shows itself by imposing its gravitational forces on everything we can see within the observable universe?

Answer 1

We can't know anything certain about the unobservable universe. It is too distant for information from it to have reached us.

It is generally believed that the universe is much larger than the part which we can observe. It may be infinitely large. There is no reason to suppose that the unobservable part of the universe is fundamentally any different from the part which we can observe.

Dark energy and dark matter are nothing to do with the observable and unobservable universe. There is dark matter in the observable universe. We can observe it, as it has a gravitational effect. But we can't see it. It probably is some as-yet-undiscovered particle.

Dark energy is also in the observable universe, but what exactly it is is very uncertain. It may just be a number in a formula: not actually "energy" at all.

When people say that only 5% of the universe is normal matter, they are speaking about the observable universe, however, there is no reason to suppose the rest of the universe is any different.

Matter that is outside the observable universe is matter. And dark matter is dark matter. But matter that is currently outside our observable universe is too far away for any information about it to reach us. This means that the gravity of that galaxy doesn't affect us. In some sense, its gravitational force has left our observable universe. (always assuming that the observable universe isn't somehow special). Remember that gravitation isn't instant. Changes in gravitational pull propagate at the speed of light.

In the ascii art below, the S represents a galaxy, and u represents you.

The galaxy is "now" outside our observable universe (the region in the / \ is observable) It has no gravitational or other effects, however it is quite reasonable to believe the ratio of matter to dark matter is the same for this galaxy as for any other.

You can't observe the galaxy "now", but you can observe its past form, since, as you see the early galaxy is in our observable part of the universe.

          S    u     ---Now----
 ^        S   / \
 |        S  /   \
 T        S /     \
 I        S/       \
 M        S         \
 E       /S          \
 ----Space---------------->

Answer 2

Your numbers are approximately those measured for the observable universe and predicted for the entire Universe, assuming the ΛCDM model (aka the standard model of cosmology) is correct. The ΛCDM model has proven to be a very precise approximation for the entire Universe, and it indicates that a geometrically flat universe which follows the cosmological principle and expands at the same rate as our Universe would have an ordinary matter density of 4.86%, a dark matter density of 25.89% and a dark energy density of 69.11%.

In 2006, the WMAP spacecraft measured the spatial geometry of the Universe to be nearly flat and determined that the observable universe consists of 4.628% ordinary matter, 24.02% dark matter and 71.35% dark energy.

Other methods have been used to confirm the accuracy of the ΛCDM model in terms of the universe's matter-energy distribution. Kowalski et al. (2008) show that supernova observations indicate 71.3% of the observable universe is composed of dark energy, whereas the other 28.7% is the total matter content.

The more advanced Planck spacecraft gave a better estimation in 2013, with its data indicating the observable universe is composed of 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy, almost exactly what the ΛCDM model predicts for the entire (approximated) Universe.

Overall, our measurements of the observable universe strongly line up with our models for the entire Universe. Keep in mind the ΛCDM model is not entirely perfect, but it approximates the Universe relatively well. While we cannot know for certain the mass-energy distribution of the entire Universe, we can predict its distribution based on the precision of our models and how closely the data for the observable universe matches up with them.