A Strange Idea

[leftrightleftrightleft]

Okay, I'm assuming there's something wrong with my logic here perhaps someone can point it out.

-It's commonly accepted that the universe is expanding at an accelerating rate.
-It's also commonly accepted that the universe's expansion is approximately 80 km/s/Mpc where 1 Mpc = 1 Megaparsec = 3.26 million light years.
-It is commonly accepted that the Doppler Effect is determined only by the velocity of the source relative to the observer or vice versa but not by the distance between them or the time elapsed because Δt is arbitrary. For an analogy, the frequency of an ambulance that just passed you won't change the farther it gets from you nor will it change from 5 seconds after passing you to 45 seconds after passing you; the frequency will only change if the ambulance accelerates.

So, lets say you take three snapshots of space (3D cross-sections of 4D spacetime if you will):

-T=0: Galaxy #2 is formed and starts emitting light. At this snapshot, the universe is expanding at 16% the speed of light.
-T= 1 Billion Years: Galaxy #1 is formed and starts emitting light. At this snapshot, the universe is expanding at 8% the speed of light. Galaxy #2 still exists as well and is expanding at 8% the speed of light.
-T = 2 billion Years: Humans now observe the two galaxies, Galaxy #2 appears to be red-shifted to give the effect of it accelerating at 16% the speed of light because the light reaching us is 2 billion years old, Galaxy #1 appears to be red-shifted to give the effect that it is accelerating at 8% the speed of light because the light reaching us is 1 billion years old. Galaxy #1 is closer to Earth and Galaxy #2 is farther from Earth but both still obey the 80 km/s/Mpc rule.

But in the 3D cross-sections, the rate of expansion is decelerating with time not accelerating. So what is the basis for scientists believing the universe is accelerating in its expansion?

Either I've stumbled on something brilliant or I am just confused. And I'm wholly convinced its the latter

 

[Wiccan_Child]

Okay, I'm assuming there's something wrong with my logic here perhaps someone can point it out.

-It's commonly accepted that the universe is expanding at an accelerating rate.
-It's also commonly accepted that the universe's expansion is approximately 80 km/s/Mpc where 1 Mpc = 1 Megaparsec = 3.26 million light years.
-It is commonly accepted that the Doppler Effect is determined only by the velocity of the source relative to the observer or vice versa but not by the distance between them or the time elapsed because Δt is arbitrary. For an analogy, the frequency of an ambulance that just passed you won't change the farther it gets from you nor will it change from 5 seconds after passing you to 45 seconds after passing you; the frequency will only change if the ambulance accelerates.

So, lets say you take three snapshots of space (3D cross-sections of 4D spacetime if you will):

-T=0: Galaxy #2 is formed and starts emitting light. At this snapshot, the universe is expanding at 16% the speed of light.
-T= 1 Billion Years: Galaxy #1 is formed and starts emitting light. At this snapshot, the universe is expanding at 8% the speed of light. Galaxy #2 still exists as well and is expanding at 8% the speed of light.
-T = 2 billion Years: Humans now observe the two galaxies, Galaxy #2 appears to be red-shifted to give the effect of it accelerating at 16% the speed of light because the light reaching us is 2 billion years old, Galaxy #1 appears to be red-shifted to give the effect that it is accelerating at 8% the speed of light because the light reaching us is 1 billion years old. Galaxy #1 is closer to Earth and Galaxy #2 is farther from Earth but both still obey the 80 km/s/Mpc rule.

But in the 3D cross-sections, the rate of expansion is decelerating with time not accelerating. So what is the basis for scientists believing the universe is accelerating in its expansion?

Either I've stumbled on something brilliant or I am just confused. And I'm wholly convinced its the latter

I think your error is that you presumed the expansion was decelerating between T=0 and T=1 - you simply stated that the expansion goes from 0.16c to 0.08c, so obviously it's decelerated.

That said, I'm not entirely sure I understand the scenario...

 

[Nostromo]

I think what lrlrl is saying the expansion rate is decreasing, but we see far galaxies at a time when the expansion rate was higher.

 

[leftrightleftrightleft]

I think your error is that you presumed the expansion was decelerating between T=0 and T=1 - you simply stated that the expansion goes from 0.16c to 0.08c, so obviously it's decelerated.

That said, I'm not entirely sure I understand the scenario...

Yes, but I'm saying that is what happened and it just appears to be accelerating. But my scenario of deceleration would give the same observed effects on Earth.

 

[Wiccan_Child]

Yes, but I'm saying that is what happened and it just appears to be accelerating. But my scenario of deceleration would give the same observed effects on Earth.

Not entirely. We can account for redshift by observing, well, redshift - spectra are just shifted x nanometres to the right (left?) of where they should be, so we can just shift them back. Then, we can measure the speed of the galaxies' recession velocities without being flummoxed by the metric expansion of spacetime.

 

[corvus_corax]

For an analogy, the frequency of an ambulance that just passed you won't change the farther it gets from you nor will it change from 5 seconds after passing you to 45 seconds after passing you; the frequency will only change if the ambulance accelerates.

Quick question here (please keep in mind I'm just a layman)-
If the ambulance speeds past me at a steady, non-varying 60 mph, are you saying that the frequency of the noise emitted by the ambulance will *not* change from my POV?
Or are you stating that acceleration (actual acceleration, as opposed to 'perceived' acceleration) happens anyway, simply due to the inertial forces (e.g. air resistance, gravity, etc) imposed on it?
Not trying to nitpick, just curious, because I have never understood the Doppler effect being dependent on *acceleration*, but simply on velocity to or from the perceiving subject.

(please, anyone, correct me if I'm wrong)

 

[Nostromo]

He's saying that once it's moving away from you at a steady speed it won't change.