Perhaps the solar system is expanding with the Universe?(adsbygoogle = window.adsbygoogle || []).push({});

For this idea to make sense one must assume that atomic lengths are constant.

The current Universal expansion rate is given by:

[tex]

\frac{\dot a}{a} = H_0

[/tex]

where a is the current scale factor and [itex]H_0[/itex] is the current Hubble parameter.

Therefore we can write the approximate expression

[tex]

\frac{\delta a}{a} = H_0 \delta t

[/tex]

Let us assume [itex]\delta t[/itex] is one year and [itex]H_0[/itex] is the reciprocal of 13 billion years.

Then in one year the Universe currently expands by the fraction [itex]7.7*10^{-11}[/itex].

Now the Earth-Moon distance is approximately [itex]3.84*10^{8}[/itex] meters.

Thus if the Solar system was generally expanding with the Universe then in a year the Earth-moon distance would increase by [itex]7.7*10^{-11} \times 3.84*10^{8}=3[/itex]cm.

This figure is similar to the measured yearly rate that the Moon is receding from the Earth. This effect is usually attributed to tidal friction transfering angular momentum from the Earth to the Moon. But the coincidence seems intriguing to me.

Maybe one could measure this effect on a geostationary satellite which is about [itex]36000[/itex]km from the center of the Earth?

In this case Universal expansion would cause the orbital distance to increase by [itex]7.7*10^{-11} \times 3.6*10^{7}=3[/itex]mm a year.

This should be measureable?

I guess the problem is that other effects such as changes in the solar wind, radiation pressure, variations in the Earth's gravitational field, and the gravitational effect of the Moon and Sun would mask any Universal expansion effect.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Is the Solar system expanding with the Universe?

**Physics Forums | Science Articles, Homework Help, Discussion**