budcamp Posted January 22, 2004 Author Share Posted January 22, 2004 At Sayonara³'s suggestion that last question was changed to... "At what distance does a given mass stop the effects of the expansion of Space relative to that mass?" Bud Link to comment Share on other sites More sharing options...
JaKiri Posted January 22, 2004 Share Posted January 22, 2004 budcamp said in post # :At Sayonara³'s suggestion that last question was changed to... "At what distance does a given mass stop the effects of the expansion of Space relative to that mass?" Bud It depends what you mean by 'the effects of the expansion of space'; if you mean the 'going apart' thing, then it depends on the mass, and the distance between the objects. Or the 'force' if you prefer. Link to comment Share on other sites More sharing options...
budcamp Posted January 22, 2004 Author Share Posted January 22, 2004 Here are a couple of answers I got from another site. Both are critical and both were very helpful. Another way of measuring cosmological motion is with respect to the Cosmic Microwave Background (CMB) radiation. The CMB is a residual field of electromagnetic radiation left over from the time when the universe was a dense hot ball of plasma. As the universe expanded though, this radiation has steadily cooled off, much like an expanding gas. However, some residual radiation is still measureable today as low level electomagnetic field which permeates all points in space. If one were to treat the universe as a blackbody [1], one could assign a temperature of about 2.7 Kelvin, with the peak frequency in microwave region of the electomagnetic spectrum. If the universe were to begin to collapse, then the temperature of the universe would begin to increase again. More importantly, one can roughly judge our motion in the universe using the CMB as a reference frame. Since the CMB should be fairly uniform at all points in space, then the universe should be observed to be the same temperature in all directions. However, there is an almost perfect dipole effect super imposed on the CMB. This means that roughly half of the sky looks slightly warmer than it should, and the other half looks slightly cooler. This dipole is induced by doppler shift due to our motion with respect to the CMB. Our galaxy, and the local group of galaxies, are all moving at about 600 km/s with respect to the CMB [2]. If one takes this relative motion into account along with the doppler [3] red-shift measured for distant galaxies, then one can pretty accurately conclude that everything is continuing to expand away from each other. As an interesting side-note, the only extra-galactic body which is not red-shifted is the Andromeda galaxy at about 2.9 million light years distant. Andromeda is actually moving towards us, and is blue shifted very slightly. This is thought to be due to the overall movement of the local group. That is to say that our galaxy and the Andromeda galaxy are moving (with respect to the CMB) towards the same region of space, and not directly towards each other. [1] http://hea-www.harvard.edu/~efortin...lack_body.shtml [2] http://www.noao.edu/noao/noaonews/sep99/node3.html [3] http://hea-www.harvard.edu/~efortin...l/Doppler.shtml __________________ Ad Astra Per Aspera Link to comment Share on other sites More sharing options...
budcamp Posted January 22, 2004 Author Share Posted January 22, 2004 It has been proved by Hubble that galaxies in the universe are not static and are all receding (moving away) from our galaxy. It has also been determined that the farther away a galaxy is the faster it is moving (greater velocity of recession). These properties have been consolidated into the formula v = H(0)r Where V = velocity of the receding galaxy r = is the radial range to that galaxy H(0) = Hubble’s constant The spectral lines emitted by a galaxy is the physical property used to determine its velocity. And it is the Doppler redshift that ultimately gives the velocity. Again this property has been consolidated into the formula lambda (0)/lambda(e) = 1 + s where lambda(0) = the wave length at which the spectral line is observed lambda(e) = the emitted wavelength of the spectral line s = the redshift both sides of the equation are unitless. Recession velocities can be measured very accurately, however distances (as in r above) can not. There is also another constraint. The distribution of galaxies must be isotropic and expand uniformly. The problem here is - Does this mean that there must be uniform distribution locally (there are clumps of matter in local surveys that do not reflect uniform distributions)? Also there are two camps on what the value for H(0) should be and it has caused considerable debate. H(0) is either 45 – 60 km s^(-1)Mpc^(-1) or 75 – 100 km s^(-1)Mpc^(-1). Again physical properties of the galaxies are very difficult to measure at great distances. The added constraint is that physical properties act the same locally as they do at great distances. Recent observations do not show a decrease in Hubble’s constant. Then again since it can’t be measured accurately any slight decrease would probably be attributed to systematic errors. Also in the standard cosmological model it is assumed (based on the Big Bang) that the universe’s expansion rate (Hubble’s constant) must have been greater at an earlier time and it is modified to indicate the decelerating effect of gravity. The assumption here is that gravity a long distance force has no limit. There are some other interesting effects such as the universe expands it also cools down. We are also in the matter epoch of the universe (that is the period of time were mater is condensating). If matter condensates and the universe cools then there are possibilities of new forces forming that have never existed before (maybe the 5th force, or the Lambda force, or the recently theorized Repulsion force). So to answer your question, and a GREAT one, my opinion, we wouldn’t know if the expansion was slowing down if it were subtle but might if it were dramatic-then again new forming forces might actually hide this initially. There is nothing like a straight forward confusing answer to nail down your thoughts! Link to comment Share on other sites More sharing options...
Radical Edward Posted January 22, 2004 Share Posted January 22, 2004 budcamp said in post # : Lambda ooh, Lambda. Link to comment Share on other sites More sharing options...
Guest Suzannah Posted January 22, 2004 Share Posted January 22, 2004 You seem to have grasped the basic concepts of cosmology, so what is the problem? I don't really see what it is you're asking. Link to comment Share on other sites More sharing options...
budcamp Posted January 22, 2004 Author Share Posted January 22, 2004 That was someone else Edward. I was showing a copy of Their answer. Bud Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 22, 2004 Share Posted January 22, 2004 budcamp said in post # :Cap'n Refsmmat You said “I know I can talk cosmology!” Well lets see what you think of these questions I asked Radical ++++++. Why is nothing blue shifted beyond a billion light years distant? Maybe because that light is so old that it doesn't show what is currently happening! Link to comment Share on other sites More sharing options...
Sayonara Posted January 22, 2004 Share Posted January 22, 2004 Can we even detect light at that extremity? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 23, 2004 Share Posted January 23, 2004 Yes, with one really long exposure time from the Hubble. Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 The hubble deep field is out about 13.5 billion light years. It took 100 hours to photograph. Bud Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 23, 2004 Share Posted January 23, 2004 That confuses me... If it keeps going behind the Earth, how can it do one long exposure? Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 I have never considered that, but if it is far enough north or south it could shoot over the pole. My first thought was of the courage of the team who used their allotted time to focus in on a completely dark area of space just to see what was there. Of course, they hit the jackpot with that one. Bud Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 23, 2004 Share Posted January 23, 2004 Even if it was in a high inclination orbit, it still passes the equator and goes to the other pole. You will have periods of Earth being in the way. That is what confuses me. Link to comment Share on other sites More sharing options...
Radical Edward Posted January 23, 2004 Share Posted January 23, 2004 budcamp said in post # :That was someone else Edward. I was showing a copy of Their answer. Bud I know. they basically said what I did. spot the link in the word "Lambda" Link to comment Share on other sites More sharing options...
Radical Edward Posted January 23, 2004 Share Posted January 23, 2004 budcamp said in post # :I have never considered that, but if it is far enough north or south it could shoot over the pole. My first thought was of the courage of the team who used their allotted time to focus in on a completely dark area of space just to see what was there. Of course, they hit the jackpot with that one. Bud I think special discression was used from the director. It was 400 orbits or something. and I suspect they turned the camera on and off. Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 I'm not sure how they did it, but I'll ask them and see what they say. Bud Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 Well they didn't turn it off and on, but I am still not sure how they kept it in focus. From NASA "In one of its most memorable observations, NASA's Hubble Space Telescope gazed into a "keyhole" piece of sky and didn't blink for 10 days. The telescope's unwavering "eyes" uncovered a galactic gold mine: a bewildering assortment of galaxies stretching back billions of years. Astronomers dubbed the area the Hubble Deep Field." Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 OK what about this? If the camara was pointing due north or due south that should work shouldn't it? I am still trying to find out exactly how it was done from NASA, but I havn't been able to contact anyone who knows. Bud Link to comment Share on other sites More sharing options...
JaKiri Posted January 23, 2004 Share Posted January 23, 2004 It's perfectly possible to have something pointing at the sun for 10 days straight; the earth just rotates below you (the orbital period would be a little under 24 hours). I'd imagine that, if the long exposure kind of thing is common, they'd set the telescope up to have that kind of orbit. Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 Suzannah' Two years ago when I first got into astronomy, I heard the cake analogy for expanding space. Then I heard about galaxies colliding. I thought, “Hey, these two don't mix.” So I started wondering if there was the possibility that space was no longer expanding. I started by thinking of what we would see if it had stopped. What would be the characteristics of a universe that had quit expanding and started to contract? When I had worked out what I thought was a pretty good example of what we should see, I started posting on astronomy forums. I got some really great feed back. I then rewrote my ideas and changed those that now seemed incorrect and tried again. I have done this a number of times, and each time I get to refine my ideas. I am currently getting feedback from several sites. Soon, I will send this to a group of professional cosmologists and see if anyone has already found a horizon, or is willing to correlate the present data to see if one is out there. Does that answer your question? Bud Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 23, 2004 Share Posted January 23, 2004 MrL_JaKiri said in post # :It's perfectly possible to have something pointing at the sun for 10 days straight; the earth just rotates below you (the orbital period would be a little under 24 hours). I'd imagine that, if the long exposure kind of thing is common, they'd set the telescope up to have that kind of orbit. No, hubble's orbit is 400 miles, that orbit takes 22.300. Link to comment Share on other sites More sharing options...
budcamp Posted January 23, 2004 Author Share Posted January 23, 2004 Would anything keep it from pointing toward one of the poles for 100 hours? Bud Link to comment Share on other sites More sharing options...
JaKiri Posted January 23, 2004 Share Posted January 23, 2004 Cap'n Refsmmat said in post # : No, hubble's orbit is 400 miles, that orbit takes 22.300. 22.3 hours? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 23, 2004 Share Posted January 23, 2004 22,300 miles. 24 hours. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now