Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: astrophysical issues

Learn more physics!

Most recent answer: 06/13/2015
Q:
Hello! I am a college student aspiring to become an astrophysicist. I have a couple of questions today and would love the physics community to answer them.#1) Do photons lose energy over the course of distance they traveled? EX.(Will a photon from a star in a different galaxy have the same same intensity as the sun does on piece of matter, say an asteroid in the asteroid belt. As well as, do they lose energy when they interact with matter?#2) How far is the temperature of space from absolute zero? #3) Will the universe continue to expand to reach absolute zero before the force of gravity can no longer compensate the expansion of space?#4) When compared to the electromagnetic spectrum, how small or large is the visible spectrum?#5) Last question! What are beyond gamma rays on the electromagnetic spectrum?
- Elias DeJesus (age 19)
New York
A:

1) Do photons lose energy over the course of distance they traveled?

They do because of the expansion of space. The wavelength gets strecthed out and the frequency reduced. 

do they lose energy when they interact with matter?

Usually, yes.

#2) How far is the temperature of space from absolute zero?

It's currently 2.725 K, in between the temperature of superfluid liquid helium and ordinary liquid helium.

#3) Will the universe continue to expand to reach absolute zero before the force of gravity can no longer compensate the expansion of space?

Ordinary gravity is already too weak to slow the expansion. The mysterious "dark energy" is accelerating the expansion. Unless something fundamental changes, the expansion will continue forever, leaving a very cold, empty universe.

#4) When compared to the electromagnetic spectrum, how small or large is the visible spectrum?

The visible spectrum covers about one factor of 2 in frequency. The electromagnetic spectrum covers a range of at least about 130 factors of 2, from the frequency at which it merges into the unified electroweak force down to the inverse of the lifetime of the universe.

#5) Last question! What are beyond gamma rays on the electromagnetic spectrum?

Does the name matter? It's all just EM waves up to the electroweak unification scale.

Mike W.

 


(published on 06/13/2015)

Follow-up on this answer.