Red/Blue Shift & Universe Origins?

Question

We all know hubbles constant, and hubbles law, right? But what is the purpose of it, besides the relationship between distance, velocity and his constant. Why did Edwin invent hubble's constant?

What's a red shift/Blue shift? I'm having problems understanding that aswell. So as the galaxy moves away, the light it emmits shifts towards the red spectrum, but why does the spectrum shift?

The probable origins of the universe are most likely from the Big Band, and I see how Hubble said that with these red shifts, the distance is getting greater between us, which suggests that the universe is expanding.

Also, outta curiousity, if the universe was expanding, including us, wouldn't the density change = 0, relative to all matter?

And if black holes squash matter to the size of a hydrogen atom, wouldn't that mean that the amount of matter is gonna be reduced to nothing, and energy is destroyed in the process, which cancells the law of conservation of energy?

I know that lol, I'm not saying that he invented it, I'm asking why does the spectrum shift...read the question please....

Answer 1

hubble's law simply gives the universe a timeline. if you follow it back far enough then it shows that the universe used to be a singularity. the constant is just that. a constant, like pi.

red shift is caused by the galaxies moving away from us, it is similar to the doppler effect but not actually the same thing since doppler only concerns sound waves.

think of a galaxy moving away from us and as it moves it emits light, light is emitted from atoms when an electron moves from one orbit to another.

so the electron moves creating one wavelength of light but by the time it emits the next wavelength it is already farther away, so to us this wavelength seems stretched.

this can be seen as red shift (if the galaxy wax coming towards us it would be a blue shift).

the density certainly is changing. eventually the density will be pretty much zero, it is already fairly close to that.

black holes do crush any matter smaller than a hydrogen atom though, a black hole squishes matter to a singularity zero radius infinite density.

the matter is still there in terms of mass, subsequently increasing the gravitational energy of the black hole, so no energy is lost it is just added to the black hole's energy.

make sense? if not just send me a note and i can try to explain it better

Answer 2

Hi. Hubble did not invent the red shift, he discovered it. In all but a few galaxies the spectral emission lines are shifted out of position toward the red end on the spectrum. In other words, their frequency has been 'stretched'. There may be another explanation, such as the light climbing out of a gravity well, that may explain this, but the best 'fit' of the data matches an overall expansion of the universe. The density in this scenario IS decreasing per unit volume, but you would only notice on a scale of cubic mega parsecs.

Edit: I did read the question..."Why did Edwin invent hubble's constant?" The black hole question is harder to answer. since we do not know anything that happens beyond the event horizon. I find it hard to believe that ANYTHING can exist inside to horizon, hydrogen atom sized or not, because it would almost HAVE to be super-luminal to exist. Make me think really hard!

Answer 3

Related to your black holes question: Energy is not destroyed. Remember that mass and energy are interchangable. At infinite densities (a black hole is for all intents and purposes infinitely dense) matter and energy are the same thing. And the energy is still there - it just isn't enough to escape the gravitation of the black hole.

Expanding universe: Yes. In fact, eventually, the universe will suffer one of two fates: either the Big Freeze or the Big Rip. In one case, matter gets too far apart for energy to transverse the gaps between objects, and the temperature of the universe drops to zero kelvin. In the other case, the Universe becomes too large and (because of how its expanding, which is in all directions from all points, like the skin of a balloon), atoms will be pulled apart from one another and the universe will become gravitationally and electro-magnetically unbound, in short order simply becoming a collection of quarks.

A red shift is related to how energy waves travel. You know how when a train blows its whistle as it moves past you, and it slowly becomes louder and higher and then as soon as it starts moving away instantly drops off in pitch and volume? That's the Doppler effect - and the same thing happens to light. As a light source moves away, the light Dopplers into the red ranges. As it moves closer, it becomes bluer.

Hubble "invented" Hubble's Constant as a fudge factor, the same as the gas constant from the ideal gas law. It's a factor which is always the same as relates to the movement of bodies away from each other. He just realized in his calculations that using this fudge factor, at THE SAME VALUE EVERY TIME, made his calculations and predictions line up with reality.

Answer 4

Light doesn't change velocity. So, unlike a person on a bike throwing a rock forward, the velocity of the rock is the sum of the velocity of the bike plus the speed of the kid's throw. Likewise, if he threw a rock *backward*, the velocity of the rock is the velocity of his throw MINUS the speed of the bike.

Photons *always* travel at 186,282.4 miles per second. So, if an object emitting them is moving away, why don't they move slower? Well - they can't. But what happens is they appear as "less energetic" - which, on the spectrum, is a shift to the red.

If the direction of the object moving is toward us, the energy is *added* to the photons it's emitting - they can't change speed, but they *can* display more energy - which is a shift toward the blue.