radiometers and the expanding universe


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Message 696325 - Posted: 31 Dec 2007, 22:43:33 UTC

So, I was remembering back to when I was playing with my dad's childhood radiometer (that bulblike scienctific instrument whose vanes spin around when light hits them). It occurred to me that the sun, and all other stars are constantly bombarding the earth (and every other object in the universe) with radiation.

It also occurred to me that my physics classes always talked about the relationship between two celestial objects in terms the famous inverse square law of gravity, their masses and rotational speed. Of course, the sun and earth are attracting each other through gravity, but because the sun is luminous, is it not also pushing the earth away like the vane of a radiometer?

Furthering that thought, could distant stars and galaxies be repelling each other like light pushes the vanes of a radiometer? Because all of these objects are floating in a vacuum and there is no force to slow them down, could this be a cause of the universe expanding and an accelerating rate?

If the sun really is repulsing the earth due to this effect, could Newton's law of gravitation need an adjustment for radiation emmiting objects?

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Message 696421 - Posted: 1 Jan 2008, 3:37:33 UTC - in response to Message 696325.

...should correct/clarify: not rotational speed... instead, angular velocity.

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Message 696626 - Posted: 2 Jan 2008, 1:54:00 UTC - in response to Message 696325.
Last modified: 2 Jan 2008, 1:58:06 UTC

It also occurred to me that my physics classes always talked about the relationship between two celestial objects in terms the famous inverse square law of gravity, their masses and rotational speed. Of course, the sun and earth are attracting each other through gravity, but because the sun is luminous, is it not also pushing the earth away like the vane of a radiometer?

Yes, but negligibly. The solar radiation that strikes the Earth amounts to about 175 petawatts. Suppose the Earth to be a giant mirror, perfectly reflective at all wavelengths, so as to maximize the effect of the radiation pressure. The force on such a mirror would be

2 × 1.75×10^17 W ÷ 3.0×10^8 m/s = 1.17×10^9 N.

Now 1.17 giganewtons (131,000 tons) may sound like an impressive force, until you compare it to the gravitational attraction between the Earth and the Sun:

6.67×10^-11 N·m^2/kg^2 × 1.99×10^30 kg × 5.97×10^24 kg ÷ (1.5×10^11 m)^2 = 3.52×10^22 N,

many orders of magnitude greater. In fact we don’t know nearly enough decimal places of any of the latter figures to be able to discern so small a difference. And of course the Earth is not a giant mirror: a great deal of the solar energy that strikes it gets converted to heat, one way or another, so has no kinematic effect.
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Message 697048 - Posted: 3 Jan 2008, 18:37:48 UTC

Back around 1953 I received a miniature Simon & Schuster book on the stars. It said that the solar radiation received at Earth amounts to about 1.5 horsepower per square yard. That compares almost exactly to 175 petawatts for the whole terrestrial disc. But could all this energy be converted into pushing the Earth? I guess that means that if the Earth were completely covered with 100%-efficient solar cells and the skies were perfectly clear those cells could generate 175 petawatts of electricity.
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Message 697090 - Posted: 3 Jan 2008, 21:09:00 UTC - in response to Message 697048.
Last modified: 3 Jan 2008, 21:11:07 UTC

Back around 1953 I received a miniature Simon & Schuster book on the stars. It said that the solar radiation received at Earth amounts to about 1.5 horsepower per square yard. That compares almost exactly to 175 petawatts for the whole terrestrial disc. But could all this energy be converted into pushing the Earth? I guess that means that if the Earth were completely covered with 100%-efficient solar cells and the skies were perfectly clear those cells could generate 175 petawatts of electricity.


I am probably missing a few facts here, but something has been troubling me about the expanding universe. It is said that space itself is expanding--The evidence for this is the red shift in the absorption lines which creates an effect that is akin to a Doppler effect.

The shifted light waves (lowered in frequency) would have less energy since the energy of a light wave is directly proportional to frequency. So the light waves have lost energy supposedly due to the expansion of space. Well --it seems just as likely to me that a light wave when traveling untold trillions of miles will encounter some drag out there in the vacuum--maybe even bumping into stray molecules along the way or otherwise affected by radiation.--maybe allot it to the "Higgs Field" ?.

What do you all think---is there further proof that the Universe is expanding (at an increasing rate over time) other than the Red Shift or is it likely that there is a much simpler explanation for the observed Red Shift.

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Daddio
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Message 697724 - Posted: 5 Jan 2008, 20:47:48 UTC - in response to Message 697090.

[…] Well --it seems just as likely to me that a light wave when traveling untold trillions of miles will encounter some drag out there in the vacuum--maybe even bumping into stray molecules along the way or otherwise affected by radiation.--maybe allot it to the "Higgs Field" ?.

What do you all think---is there further proof that the Universe is expanding (at an increasing rate over time) other than the Red Shift or is it likely that there is a much simpler explanation for the observed Red Shift.

Such an explanation for cosmological red-shifts was proposed by Fritz Zwicky about 75 years ago. The main problem with this idea is that all known mechanisms by which light loses energy—other than the Doppler effect—would have consequences that are not actually observed. See Ned Wright’s Cosmology Tutorial on “tired light” for some details of the objections.

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Message 697897 - Posted: 6 Jan 2008, 17:51:31 UTC - in response to Message 697724.

[quote][…] Well --it seems just as likely to me that a light wave when traveling untold trillions of miles will encounter some drag out there in the vacuum--maybe even bumping into stray molecules along the way or otherwise affected by radiation.--maybe allot it to the "Higgs Field" ?.

What do you all think---is there further proof that the Universe is expanding (at an increasing rate over time) other than the Red Shift or is it likely that there is a much simpler explanation for the observed Red Shift.

Such an explanation for cosmological red-shifts was proposed by Fritz Zwicky about 75 years ago. The main problem with this idea is that all known mechanisms by which light loses energy—other than the Doppler effect—would have consequences that are not actually observed. See Ned Wright’s Cosmology Tutorial on “tired light” for some details of the objections.
[/quoteTHANKYOU--

I will follow up on your reference and continue my puzzlement with less uncertainty I am sure. As for the energy of the vacuum...I am thinking that it takes a lot of energy here on earth to produce a near vacuum--Maybe nature trying to fill the vacuum is the essence of dark energy
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Message 698086 - Posted: 7 Jan 2008, 6:12:15 UTC - in response to Message 696626.
Last modified: 7 Jan 2008, 6:16:49 UTC

many orders of magnitude greater.

From something I read recently, isn't '1 Order' 10^1? (As in, 2 order=(2*10^1)*=20*?). I just want to make sure of something while I'm reading this...

And of course the Earth is not a giant mirror: a great deal of the solar energy that strikes it gets converted to heat, one way or another, so has no kinematic effect.

Just thinking aloud, here...
Mass and energy are two ways of looking at "the same thing."
Assuming Earth was a 'perfect' mirror, then any light would be converted entirely into momentum (velocity) away from the light source.
Any light not converted into momentum would be converted into:

    1. Heat (Infrared Light)
    2. Light ('Visible' or ultraviolet)
    3. Mass (Some form of matter creation- or at least changing particles to higher-mass particles.)


Point 3 would serve to counteract (slow down) part (if not all) of the velocity gained under the light-momentum/velocity -> Earth-momentum/velocity view. In my opinion, of course.
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Message 698231 - Posted: 7 Jan 2008, 21:39:04 UTC - in response to Message 698086.

From something I read recently, isn't '1 Order' 10^1? (As in, 2 order=(2*10^1)*=20*?). I just want to make sure of something while I'm reading this...

Orders of magnitude normally refer to the exponent. So 2nd order is 10^2, 3rd is 10^3.
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Message 698803 - Posted: 10 Jan 2008, 5:26:00 UTC
Last modified: 10 Jan 2008, 5:26:12 UTC

Just to expand a bit on what KK wrote, you can compare to figures in orders of magnitude by taking common (base-ten) logarithms. To make my “many” upthread more precise, either:


  • take the log of the quotient
    log(3.52×10^22 ÷ 1.17×10^9) = log(3.01×10^13) = 13.48
    or
  • subtract logs
    log(3.52×10^22) – log(1.17×10^9) = 22.55 – 9.07 = 13.48


—thirteen and a half orders of magnitude.

Note that the expression is informal, at the same level as “rules of thumb”; avoid confusing this usage with standard magnitude scales that may use different bases. For example the scale of stellar magnitudes used by astronomers goes by powers of 10^(2/5), so that a five-magnitude difference represents a factor of one hundred in luminosity. (This base was chosen to approximate the traditional, subjective classification.) In another realm altogether, you can find how many octaves there are between two musical notes by the same procedure as above, but taking the binary (base-two) logarithms of their frequencies.

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Message 699120 - Posted: 11 Jan 2008, 8:50:20 UTC - in response to Message 698803.

Orders of magnitude normally refer to the exponent. So 2nd order is 10^2, 3rd is 10^3.

To make my “many” upthread more precise, either:


* take the log of the quotient
log(3.52×10^22 ÷ 1.17×10^9) = log(3.01×10^13) = 13.48
or
* subtract logs
log(3.52×10^22) – log(1.17×10^9) = 22.55 – 9.07 = 13.48


—thirteen and a half orders of magnitude.

Thanks.
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Message 704831 - Posted: 27 Jan 2008, 14:36:23 UTC - in response to Message 696325.

So, I was remembering back to when I was playing with my dad's childhood radiometer (that bulblike scienctific instrument whose vanes spin around when light hits them). It occurred to me that the sun, and all other stars are constantly bombarding the earth (and every other object in the universe) with radiation.

It also occurred to me that my physics classes always talked about the relationship between two celestial objects in terms the famous inverse square law of gravity, their masses and rotational speed. Of course, the sun and earth are attracting each other through gravity, but because the sun is luminous, is it not also pushing the earth away like the vane of a radiometer?

Furthering that thought, could distant stars and galaxies be repelling each other like light pushes the vanes of a radiometer? Because all of these objects are floating in a vacuum and there is no force to slow them down, could this be a cause of the universe expanding and an accelerating rate?

If the sun really is repulsing the earth due to this effect, could Newton's law of gravitation need an adjustment for radiation emmiting objects?


no.

ok ill add a bit more info, the sun dosnt have a static amount of luminesence, so the push you sugest should go up and down, but there is no sogn of this, so, no it dosnt.

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Message 704835 - Posted: 27 Jan 2008, 14:52:17 UTC
Last modified: 27 Jan 2008, 14:54:14 UTC

to those that think the univers is pushing at the earth, the earth is a spherical object, though not that spherical and is sourounded by the univers, so energy is pushing from all around, surly most of it is canceling the itself out?

so even if it was possible, and im not sayning it is, most of the energy hitting the earth is canceling itself out, in the same way that the energy hiting the earth on the side of the sun isnt pushing us off into space like a rocket, its simple, gravity though a week force in the univers is holding most things in place, and helping other things to move, such as comets, satelights, we eaven use stelar objects to help with getting our satelights and spacecraft into orbit round solar bodies, but i dont here much about alowing for stelar or solar winds in these computations, i wonder why?

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