Science Questions

If the universe is expanding, are we getting further from the Sun?

Sat, 14th Aug 2010

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Dave Green asked:

Hi guys, love the show, listen to it at work to help make the days a bit more interesting. My question is: If the universe is expanding, but planets and stars are staying the same size, why doesn't the distance between Earth and the sun increase, and our orbit around the sun become longer, thus lengthening our year over time, and eventually cooling the Earth due to its distance?


We put this question to Dr Carolin Crawford:

Carolin -   Well this is about, not so much from the effects of dark matter on our solar system, but looking at more the effects of dark energy Ė so staying on the dark side.  Space is expanding and itís carrying the galaxies along with it for the ride.  They're all receding from us, and we think they're being pushed apart by a force that we call dark energy, and this is currently accelerating the expansion of the universe.

But the curious thing is, that this dark energy, whatever it is, is a property of space.  So the larger the distance between bodies, the stronger they push to drive them apart.  Conversely, gravity - which weíre a bit more used to - is a property of matter, and itís a pulling force, so that opposes the expansion, and the gravitational pull is stronger the more mass thatís there, and depends on how close you are to it.

So, whether the pull of gravity, or the push of dark energy dominates over a given region of the universe, depends on how much mass is there, and how widely separated it is.  If they're far apart, the push of the dark energy wins, but if they're close together, gravity is going to dominate. 

You have to remember, in astronomical terms, our solar system is absolutely tiny.  The planets and the sun, and all the constituents of our solar system, are very close together, and thereís no question that gravity wins in that circumstance. 

Even on the scales of the galaxy, gravity is the dominating force.  Even between groups or clusters of galaxies, gravity is gluing them together. You're only going to get this expansion of space on the very largest scales, where you have sufficient space that the dark energy can dominate.


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Dave Green asked the Naked Scientists: Hi guys, love the show, listen to it at work to help make the days a bit more interesting. My question is: If the universe is expanding but planets and stars are staying the same size, why doesn't the distance between Earth and the Sun increase and our orbit around the sun become longer, thus lengthening our year over time and cooling the Earth? What do you think? Dave Green, Tue, 26th Jan 2010

Sweet question :)

I can see some arguments here.

1. Space only expands through 'free space' and the 'space' we have here between planets and suns are too 'diluted' to be 'free (absolutely empty) space'.

That arguments then would support the concept of there existing 4-real that unattainable ideal, described as an equivalent to the concept of 'absolute Zero'.

2. Space 'expands' in all points, not bothering for it to be 'free'.

Which lead us to your question and then to why we can't validate it inside the solar system? But also lead us to the question how it separate between that 'diluted space' here and matter?

If you look at a atom it's 99.999~ space?
( if I remember right :)


You might also argue that the expansion only can take place where there is no strong electrical bonds as f. ex. between electrons and their nuclei, and if space is naturally 'diluted' there will be such everywhere. But then you will need it to exist 'free space' too for that expansion to happen.

yor_on, Tue, 26th Jan 2010

No. the expansion of space effectively passes by all strongly gravitating bodies right up to the scale of clusters of galaxies.

Also on the scale of the solar system this expansion is totally miniscule but could be detected if it occurred in ranging experiments with spacecraft which measure distances of millions of miles to a few centimetres. Soul Surfer, Tue, 26th Jan 2010

"By characterizing the detailed structure of the cosmic microwave background fluctuations, WMAP has accurately determined the basic cosmological parameters, including the Hubble constant, to better than 5%. This measurement is completely independent of traditional measurements using Cepheid variables and other techniques. The current results show the Hubble Constant to be 73.5 (km/sec)/Mpc (give or take 3.2 (km/sec)/Mpc). If the WMAP data is combined with other cosmological data, the best estimate is 70.8 (km/sec)/Mpc (give or take 1.6 (km/sec)/Mpc). These results assume that the universe is spatially flat, which is consistent with all available data. However, if we do not make this assumption, the uncertainty in the Hubble constant increases to 4 (km/sec)/Mpc, or slightly over 5%.2" 

70.8 (km/sec)/Mpc == 70.8 km per second per 3.26 million light years and why you have three factors here has to do with the fact that it is space that seems to grow expanding as rings on the water, which means that 70.8/km per sec is only correct up to one Mpc (Megaparsec).

Which if we downgrade it to distance per light year then would become truly minuscule. - 78 000 m per second split with 3.26 million light years - (approximately 0.024 m or, 2.4 cm per Second per light year if I'm correct? which we then would have to split with 365 days times twenty four hours times sixty minutes (approximately that is:) gives us 2.4 cm per second split with 525 600 minutes (-> one light year) which will give us 4,56621004566210045662100456621e-6 cm per second per light minute if i understood this right? But then on the other hand it adds up, every second does. And as one second goes 31536000 in a year we would in one year see the distance grow 144 cm per one light minute (as seen over a distance of one Megaparsec, as the 'constant' working here?) and then also assuming that the factor really is 70.8 (km/sec)/Mpc.

Not sure if this makes sense or not.
Awh :)

So yeah, I can see the problem, as the distances we have inside our solar system counts only in light minutes at most.

But it sure seems weird to me. Considering that we get a number here that measures a distance growing, it seems then that we should be able to look at Planck size and then say how many Planck size this possible extremely generalized measurement would take too? :::)))

Nah, don't take me to seriously here..

But still? one Planck size per ** per*** per*** etc etc :)

Hubble constant

"The common unit of velocity used to measure the speed of a galaxy is km/sec, while the most common unit of for measuring the distance to nearby galaxies is called the Megaparsec (Mpc) which is equal to 3.26 million light years or 30,800,000,000,000,000,000 km! Thus the units of the Hubble constant are (km/sec)/Mpc. "


Sort of 'quasi logical' this one and up the walls too, but sort of fun even though it doesn't tell me a thing about why and where it is thought that our 'space' expands. It still seems that it should have something to do with Planck size to me? As that is the smallest measurement that makes sense to us?? yor_on, Tue, 26th Jan 2010

How about this then?
Assume that gravitation creates from mass with acceleration as a very distant cousin :)
Assume that 'expansion' need a 'disallowance' of gravity.
Then, where gravity breaks down to a certain 'strength' space expands.

But then space would be needed to be something different, it seems to me, than what we can see near VMO:s (Very Massive Objects) as we then say that 'space' expands inside f.ex. a Black Hole?

And if it 'expands' due to the unavailability of gravity it seems suddenly to be some sort of medium too? Like some inversed rubber band wanting to 'expand' perhaps, but held together by 'gravity'?

Am I certified now :) yor_on, Wed, 27th Jan 2010

No. But you may be certifiable.

      (OK, OK! It was a joke. Sheesh!) Geezer, Wed, 27th Jan 2010

yor_on, Thu, 28th Jan 2010

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