Redshift - Sixty Symbols

You've heard of redshift, but what about the "blue shifting galaxy" on a collision course with the Milky Way!?

More astronomy at http://www.sixtysymbols.com/

Category:

Science & Technology

Tags:

• redshift
• galaxy
• andromeda

[bliss314159]

one of my fav videos!

[sixtysymbols]

@bliss314159: Thanks, glad you liked it!

[mylhs]

tha analogy of a baloon as expanding universe is beautiful!

[Taste3339]

Can anyone tell me whether you can tell how far that galaxy has travelled from its original position. If it had a redshift of say 5? And how its possible to map the universe if all the things that we see have moved.

[Kaeralho]

@pseudorandomly I figured so much, but being just someone who takes interest in physics (not studying physics YET) I felt confused. thank you very much for clarifying, sir.

long days, beautiful nights.

[pseudorandomly]

@beno2367

"... still not sure about light stretching with space ..." Think about it this way: protons don't stretch with space, because the color force binding the quarks together inside the proton is far stronger than necessary to overcome the very slight stretching of space over that distance. But there is no force holding the wave crests of light together, so even the tiny effect of the stretching of space is enough to elongate the waves.

[pseudorandomly]

@pseudorandomly

(cont) ... either toward or away from us, and probably small in speed.

Over cosmological distances, however, we observe that *all* galaxies are moving away from us, with speeds that increase essentially linearly with distance. This is best explained by the space between the galaxies actually growing larger with time, rather than the motion of the galaxies *through* space. This is termed "cosmological" redshift.

[pseudorandomly]

@beno2367

Light is emitted at *all* frequencies all the time, and you're right -- light that was emitted when the Universe was half the present size would be stretched by that same factor now. There's really nothing odd about that.

Redshift *can* be caused by a doppler effect -- that's how we detect that stars in our galaxy are moving toward or away from us, or how we know the Andromeda Galaxy is headed toward us. But such "secular" motions of galaxies would be random, ... (cont)

[beno2367]

@pseudorandomly yeah, that makes sense. i think it was even the electro-strong-weak force at the very beginning.

I'm still not sure about light stretching with space, because even when the universe was half the size, all the frequencies would be doubled. and i don't know about that

i thought the red shift was simply the doppler effect with light, just effected by the speed, not space stretching, or does one go with the other? but then shouldn't relativity stop a red shift? Im thinking too much

[pseudorandomly]

@Kaeralho

Well, in the technical sense, there are other photons -- there are "virtual photons" which are the carriers of the electromagnetic force. But in the sense the speaker in the video means it, no -- he was just saying "of light" as a manner of expression. Note that x-rays, gamma rays, and radio waves are also photons, and, to a physicist, in a certain sense they are ALL "light".

[pseudorandomly]

@crazyboyandyomama

You're rediscovered special relativity. It doesn't matter whether you think of yourself as standing still and the galaxy as moving, or vice versa -- the effect is the same. In fact, it is meaningless to say "I am not moving", because I would then ask "compared to what?' You're not moving with respect to your chair, but you *are* moving with respect to the Sun, the center of the galaxy, and the Virgo cluster, etc.

[pseudorandomly]

@davidandkaze

Redshifts do not appreciably change over such short intervals of time -- think in terms of millions of years instead. But you're right: if the Universe is expanding ever faster as time goes on (and there are good reasons to believe this is so), galaxies will recede faster and faster as time goes on. However, galaxies are much too far away to measure distances with parallax as you suggest; we can only measure distances to the nearest stars by that method.

[pseudorandomly]

@beno2367

No, matter does not stretch, because there are powerful forces (strong force and electromagnetism) that hold matter together. You make an interesting point about light when the Universe was still extremely tiny (far smaller than a proton) and had not yet undergone inflation; it's one reason we don't really have much of an understanding of what the Universe was like at that time. Electromagnetism could not exist yet as a separate force; it was bound up with the weak force.