citybadger t1_j59r94t wrote

Light climbing out a gravity well loses energy. Unlike a object with mass, it doesn’t slow down as it loses energy, because it’s light - it can’t slow down. So it instead gets lower in frequency - “red-shifted”. Gamma rays become X-rays, which become ultraviolet light, which become blue visible light, which become red visible light, then infrared, microwave, and radio. Visible light climbing out of ordinary neutron star will be red shifted. Some of the red light will be invisible because it shifted into infrared.


citybadger t1_j1dpz84 wrote

The amount of the frosting isn’t relevant. It the way it’s cracked. Specifically we can see how much the CMB light is “stretched” and figure out how old is is from that. The amount of CMB does not factor into that.

We can aim a lot of sensors towards a rock in North America, including our eyes and sense of touch, but also laser spectrographs and electron microscopes. We can aim the same sensors at a rock in India, get the same results, and conclude the rocks are made of the same stuff.

We can aim fewer (but an increasing number!) of sensors at a rock on Mars, for those we get the same results as some rocks on Earth, so we conclude, with slightly less confidence, that the rock on Mars is composed of the same stuff as the rock on Earth.

We can aim even fewer sensors at a rock (well, a glowing dust cloud, rocks are too small and dark to see) in another galaxy. Those sensor readings (spectroscopy in particular) match readings taken from stuff here on Earth, we conclude that the dust cloud in that galaxy is probably made up of the same stuff as we have here. Maybe not, but if it looks like hydrogen, and behaves like hydrogen when heated, it’s probably hydrogen right?