Shadowy Man

Sidian:

Yes, these motions are taken into account. When the cosmological redshift is converted into velocity through the Hubble constant you will find that these "expansion" velocities are much greater than these "local" velocities for most external galaxies.

Sidian

what exactly is quantized and what about an LED proves the universe is quantized...i'm a newb =(

Demosthenes

Basically quantized means that matter and energy cannot take continuous values but it can only assume discrete values which are multiples of the Planck's constant, h. So far, we've proved that matter and energy, even the motion of objects as it falls under gravity is quantized.

So we also expect that spacetime is quantized too, however, christopher lord, a LED does not prove that space time is quantized, all it does it show that matter and energy is quantized. We still have a while to go before we're able to develop means to detect the discretness of spacetime, we don't even have a viable theory to describe such a state. The current work in superstring theories barely have begun to address that.

Ernest Sparks

Remember that "Big Bang" started with a BBC radio lecture by Fred Hoyle, where he meant to ridicule the evolutionary universe model of Gamow and his students, Alpher and Herman, from a presumed initial hot, dense state,with generation of chemical elements from interactions of nucleons. The name is memorable, and so it got adopted with pride as a name when this field became popular, especially in the 1960s. Many pundits have cautioned that it is not really an explosion, like a sudden release of pressure accompanied by vibrations through a surrounding medium. I believe that it is still an open question whether the Big "Bang" is just something big, or whether it is the absolute first event. General Relativity asserts that spacetime relationships are modified by presence of gravitating masses/energies, but it is not totally clear there just how space and time can originate that way. If it is true, then that takes another theory, such as a quantum gravity theory, that goes beyond General Relativity.

While I am addressing this subject, it is interesting that Einstein and most other classical GR cosmologists derive the curvilinear character of space using a 4-dimensional space substrate or of spacetime using a 5-dimensional spacetime substrate. Then they bind a part of it by substituting with normal 3-dimensional space coordinates or 4-dimensional spacetime coordinates. This is a hypersurface and represents the "real" universe from that point on. The original larger substrate is forgotten. I think of this whenever I read about more modern theories with extra dimensions.

Ernie

DigitalDruid

Sidian,

Taking into account all of these factors you mention could be one way to determine the expansion. But there is a simpler way; that's what Hubble used. Basically, if the galaxies are accelerating relative to one another the light received from the galaxies should show red-shift. That does not mean there is no true acceleration since acceleration and velocity are always with respect to some refernce.

The effect is called doppler efect in general terms. All wave-based phenomena (light, sound)exhibit it. You might have noticed the siren pitch of a fast receeding ambulance going down progressively. That tells you there is relativee acceleration - the two obejcts are either moving apart (pitch growing less shriller) or approaching each other (pitch growing shriller). Now your doppler-effect based determination would be true irrespective of all the other motions the two objects might be undergoing. Suppose you are not standing on roadside, but roller-skating. Still, if you notice the doppler effect you can be sure you are either moving apart or nearer the ambulance. Only if the ambulance maintains constant velocity relative to you, the dopppler effect would vanish, and you would hear a constant wail at same pitch.

Similary in case of two galaxies, if the sum-total of all the motions they undrgo amounted to two galaxies not accelerating relative to one another, then we should not have observed red-shift. But we do. So the red-shift indicates the galaxies are moving apart in actual sense.

The red-shift has been observed between our galaxies and all distant galaxies. However locally that need not be true. For example, our galaxy and the nearest andromeda galaxy are moving closer due to gravity. However together both are still hurtling away from other galaxies. One complexity of applying Hubble's law is to take into account such local coupling between galaxies.

Sidian

aha!

so red-shift is doppler for light basically? or is it a detected change in doppler for light?

i understood that light, from whatever launching point, always traveled the same speed. so how does any doppler effect affect us?

if we notice a change in the light's waves, how does that show anything other than that we are moving? no matter what speed the object we are looking at was traveling when the light left it...the light hits us going 300,000 km/s right?

i'm so newb to this stuff =(

Shadowy Man

Yes, the doppler effect does not affect the speed of wave phenomenon, only its wavelength.

DigitalDruid

I think you are asking great questions. We are all newbie in so many things. I myself am learning all the time in this forum.

Yeah it is doppler for light basically. I would say it is "detected" change. It is appranet change because depending on how fast you are moving the light from the source (galaxy) would show different amounts of frequency shift.

This shift can happen on our earth itself. I remember a physics quiz where I was asked at what speed my car must approach a red traffic light so that I see it green! If you calculate you find that if the car moves at a certain fraction of the speed of light, you would see a red light to be green! It's good that our cars do not move anywhere near that speed!

The redshift does not violate the constant speed
of light principle. Speed of propagation of a wave can be written as:

speed = wavelength / Periodic-time
where, wavelength is the distance from one crest of the wave to the next crest;
and, Periodic-time is the time taken to propagate through one cycle of the wave (basically, the same linear distance as one wavelength).

Now, notice that if the wavelength and Periodic-time both change (as "oberved" by a moving observer)by the same factor , the speed would remain the same. So doppler effect can be observed for light even though speed of light is constant.

DNAunion

DNAunion: Yes.

DNAunion: This is called "peculiar motion" and is taken into account.

DNAunion: We know the rate at which the Earth travels around our Sun. If the rate that a galaxy is receding from us is greater than that value - and the more distant galaxies are moving away from us at VASTLY greater speeds - then it cannot be attributed to our motion around the Sun. We also know how it takes our Sun/solar system to orbit the Milky Way, and the velocities of distant galaxies away from us is much greater than our velocity around our own galaxy. That basically leaves only the motion of one galaxy relative to another to explain the tremendous velocities (such as 0.8 c).

DNAunion: Kind of a nit pick. But not all galaxies are moving away from us. In about 3 billion years, I believe, our Milky Way is going to "collide" with a galaxy (the Andromeda galaxy, IIRC) that is approaching ours (yes, from their point of view, we are approaching them).

DNAunion: The galaxies near the edge of our Hubble sphere are receding from us at around 0.8c: that is, 80% the speed of light. That is VASTLY greater than our velocity around the Sun and around the nucleus of the Milky Way.

DNAunion: Not everything is moving away from us - more than one NEARBY galaxy is approaching us.

DNAunion

DNAunion: For distant galaxies, IIRC, lengthening of the wavelength of light by expansion of intervening space itself contributes more to the light's red-shift than the Dopler effect does.

DNAunion: Yes, the speed of light is independent of the speed of its source - and is also independent of the speed of the receiver.

For light being redshifted, what gets changed is not the speed of the wave, but the wavelength (light that has been redshifted has longer wavelength).

DNAunion: Yes, the speed of light we receive would be the same, no matter how close or far away a star or galaxy is. We have to look at the wavelength to judge distance. The greater the redshift, the greater the "distortion" of the light. Here, "distortion" could be due to (1) relative motion of the source and destination, and/or (2) expansion of space stretching the light waves en route.