14 billion years

5000 years

380,000 years

It depends on which direction they come from.

About 3 K, because wavelength is unrelated to the peak temperature.

Less than 3 K, because lower temperatures correspond to longer wavelengths.

More than 3 K, because by the time the peak temperature is 10 mm, the Universe will be contracting.

Less than 3 K, because the Universe slowly cools down over time.

About 3 K, because temperature won’t change significantly with such a small change in wavelength.

More than 3 K, because higher temperatures correspond to longer wavelengths.

The spectrum of 75 percent hydrogen and 25 percent helium is a perfect thermal radiation spectrum.

This radiation came from the heat of the Universe itself.

The dark matter in the Universe is a perfect thermal radiation spectrum."

The spectrum of pure hydrogen is a perfect thermal radiation spectrum.

This radiation came from the temperature of the Universe.

The first stars that formed in the Universe must all have had the same temperature.

The light from all the stars and gas in the sky averaged over the entire Universe is a perfect thermal radiation spectrum.

3 minutes

10^-100 seconds

300,000 years

300 years

10^-10 seconds

1 million years

10^10 seconds

hotter.

larger.

cooler.