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Omnipresent Atheists Message Board Omnipresent Atheists Discussion Forum › Accelerating? Expansion of Universe

Accelerating? Expansion of Universe

David N.
DaveNohle
Columbus, OH
Post #: 4
Tuesday at OA, we discussed a question regarding the expanding universe. I'm not clear exactly what the question was but it regarded how the expansion of the universe could be accelerating. Can anyone find where this claim is made? I just spent a few minutes looking and what I found (at http://map.gsfc.nasa....­) is this:

"Hubble's second revolutionary discovery was based on comparing his measurements of the Cepheid-based galaxy distance determinations with measurements of the relative velocities of these galaxies. He showed that more distant galaxies were moving away from us more rapidly:
v = Hod
where v is the speed at which a galaxy moves away from us, and d is its distance. The constant of proportionality Ho is now called the Hubble constant."

This seems to claim instead that more distant galaxies are moving faster than closer ones but not that they are accelerating. Does anyone know if this correct?
Sergio
user 11956934
Columbus, OH
Post #: 2
Tuesday at OA, we discussed a question regarding the expanding universe. I'm not clear exactly what the question was but it regarded how the expansion of the universe could be accelerating. Can anyone find where this claim is made? I just spent a few minutes looking and what I found (at http://map.gsfc.nasa....­) is this:

"Hubble's second revolutionary discovery was based on comparing his measurements of the Cepheid-based galaxy distance determinations with measurements of the relative velocities of these galaxies. He showed that more distant galaxies were moving away from us more rapidly:
v = Hod
where v is the speed at which a galaxy moves away from us, and d is its distance. The constant of proportionality Ho is now called the Hubble constant."

This seems to claim instead that more distant galaxies are moving faster than closer ones but not that they are accelerating. Does anyone know if this correct?


A simple but assertive article about the topic can be found at Wikipedia. Just google "Accelerating Universe Wikipedia"
David N.
DaveNohle
Columbus, OH
Post #: 5
Thanks Sergio. That reference had both the claim and the explanation: "Models attempting to explain accelerating expansion include some form of dark energy: Cosmological Constant, Quintessence, Dark Fluid or Phantom energy. The most important property of dark energy is that it has negative pressure which is distributed relatively homogeneously in space"
A former member
Post #: 1
Hi everyone! I'm new to this group and just wanted to throw my 2 cents into this discussion.

My background in physics is limited to what I learned in high school, so the following is offered only as food for thought and not a challenge upon those far smarter than me on these issues.

From my limited understanding, the theory that the universe is expanding is based upon the doppler red-shift effect. That the further light is travels in space, the more it shifts.

This limited understanding is what I recall from that physics class some 30 years ago, so please feel free to correct me anyone.

At any rate, the problem I always had with this theory was that it did not take into consideration the nature of what a photon of light may actually be. What if all light (EM radiation) consists of standing waves that bounce back and forth between two nodes. Forget for the moment what would physically define such nodes, but just like waves in a pond diminish after a stone is tossed in; it seems reasonable to imagine that a standing wave between two nodes in orbit around each other traveling through interstellar space would also diminish.

What if it was the diminishment of this standing wave that caused the "red-shift"? It seems to me that the whole expanding universe theory would go down the tubes.

At any rate, these were my thoughts some 25 years ago, and I have not thought much about it since.
David N.
DaveNohle
Columbus, OH
Post #: 6
(Hi Stephen!)

I'm no expert either but assume that waves in a pond diminish due to friction. I'm not sure what, if anything, causes light waves to diminish (my physics is dated too).

I wonder if there is some confusion of cause and effect here: we detect expansion of the universe because the light is traveling from a moving (and shining) source and the light has a frequency shift due to that motion but the light is not causing or affecting the shining or the star's motion.

An analogy with sound waves: An observer hearing a blaring ambulance approaching hears a different frequency-shift-induced change in pitch while at the same time a different observer may hear the ambulance moving away with a different pitch change (and the driver hears a constant siren without doppler effect). What any observer hears does not change what the siren is emitting or the motion of the ambulance.
A former member
Post #: 45
It's not that they diminish, it's that they stretch. Light is a wave with crests and troughs. It has, obviously, a wavelength. Now, since we know the wavelength and the speed of the light ( c ), we know how much time it takes from crest to the next crest to pass a given point. If the object is moving, you can know how far it moves in this length of time. Now, generally, things are moving slowly enough that this distance is SUPER SUPER SUPER tiny, even compared to the very tiny wavelengths of visible light (hundreds of nanometers). But, if the object emitting the light is really moving, it can 'add' a detectable amount of distance from crest to crest (or trough to trough, if you prefer) as the light is emitted. This is the classical (meaning ignoring special relativity) explanation for the Doppler effect. It's exactly why sound pitches higher as something approaches and lower as it recedes - because the speed of sound is not so high that we can't move at a small fraction of it, at least in a car or train. The same explanation holds for light if the object isn't going too close to c. If it's going a sizable fraction of c then special relativistic effects become more and more significant and the classical explanation becomes less and less accurate, but conceptually it's probably good enough for most of us.
Dean B.
Barboian
Columbus, OH
Post #: 2
Cary sound right to me from my limited knowledge as well. Being that none of us seem to be astrophysicists, I have to take the word of true astrophysicists. I have come to trust the scientific method and the opinions of those that study this stuff for a lifetime. This isn't faith, but instead it is trust in those that know much much more than I.

That being said, the fact that they are still learning that the universe is accelerating and the prescence of things such as dark matter affecting how objects in the universe move is proof that we are still infants fumbling around with only a child's book to guide us and a binkie. Physicists are coming up with changes and permutations of the theories of the universe dependent upon each new discovery. There is so much we don't know yet. The fabric of the universe is still largely a mystery. One of the theories that I like is that this universe is derived from the intersection of 2 other planes of reality, and gravity is a force that moves thru multiple dimensions since it is so weak compared to the other forces. Dark matter may be the anchoring points intersecting with other parallel universes and we may be accelerating due to twisting and contorting of these parallel planes squishing us around. Fascinating, but highly unproveable at this point.

The problem is most people cannot look at such enormity and mystery without their brains starting to smoke and they throw their hands in the air and say that it is a god. There is no morality here. We are ants trapped on a piece of flotsam adrift in the sea.
David N.
DaveNohle
Columbus, OH
Post #: 7
It's not that they diminish, it's that they stretch.
I don't think that Cary was referring to waves in ponds here but just to make sure that I have this straight am posting this clarification for further criticism. "Diminishing" refers to declining amplitude (the height of the wave) and definitely happens in water - otherwise a splash in the ocean off the West coast of Ireland would create a wave that would reach the US at the original height (assuming same water depth where measured). Frequency changes associated with Doppler effects are waves perceived as stretched due to relative velocity.
A former member
Post #: 46
"Diminishing" refers to declining amplitude (the height of the wave) ...

Yep - I was referring to wavelength, i.e. taking "diminishing" to refer to amplitude, the value of which doesn't affect color or pitch but rather brightness or loudness.

Obviously waves do diminish as they spread, generally according to the the inverse square law (in 3 dimensions at least), but this isn't a relativistic effect.
A former member
Post #: 7
Hi David and Cary,

I'm trying to imagine a single photon impacting on a hypothetical detector attached to the ISS (International Space Station).

Our detector measures the photon's wavelength, speed, and amplitude.

According to Richard Feynman "...there is also an amplitude for light to go faster (or slower) than the conventional speed of light. " 1

I believe the the word "amplitude" can mean either:

(a) a volume level, [For example: Using a dimmer-switch on light bulb causes the brightness level in a room to change, because the number of photons being emitted from the bulb is increased or decreased.], or

(b) a wave height level, [the distance between a wave's crest and its trough.]

Referring to the second meaning of the word amplitude, it would seem logical that a photon's wavelength and amplitude are correlated.


NOW, back to the Expanding Universe Theory ("EUT"): When our detector on the ISS detects a photon that was first emitted hundreds of thousands of light years away, [a photon whose red-shift can be computed because it was emitted from a process that we understand only generates photons of a given wavelength], the EUT presumes that the red-shift is the result of space expanding between the ISS and the point of the photon's emission.

What if, the EUT presumption is incorrect and the red-shift is in reality the result of a diminished wave height amplitude? An effect which could be due to some type of decay effect upon the photon itself taking place over the span of thousands of years during its interstellar travel.




______________________________________­____________________________
Footnotes:

1. Varying c in quantum theory - http://en.wikipedia.o...­
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