Brane power to the max, cont

1. Brane power to the max, cont Besides the existence of another universe, BPM has two special features (at least); 1. We won’t find and non-baryonic dark matter because there isn’t any. Rather the gravitational interaction with the other Universe mimics this effect. 2. We won’t find gravitational radiation

2. General Considerations continued • Howlong is it going to take me? • How much is it going to cost? • Are the time and money worth it?

3. Other Considerations • When to hold’em and when to fold’em • What are the cost drivers in my design? • Do I need any instrument development to allow me to achieve my goals? • Do I have all the skills I need? • If not, can I assemble a winning team?

4. Technical Considerations • What limits the accuracy of my measurement? • How will I calibrate my measurements so that somebody else can judge the results. • What assumptions will I have to make from theory or experiment to build my case. • If I’m looking for an effect (such as WIMPs), will my result be interesting even if I don’t find the effect?

5. Why Distance • Why bother with the distance scale? • Because nearly every thing we derive in astronomy depends on knowing the distance. • For cosmology, we want to know: • The expansion rate (Hubble constant) which requires distance versus velocity measurements. • We want to measure the mass density of the universe, we need to know the mass within a given volume, which means a knowledge of the distance.

6. Why Distance • For cosmology, we want to know: • The distance along with a measure of the redshift so we can test different geometries of the Universe • The distance to objects can tell us how these objects form and evolve. • The spatial distribution objects is another test of cosmology.

7. Back to distance • Overall design calls for a “bootstrap” approach. • Begin with small distances we can effectively measure with a ruler. • Then use “parallax” can tell us distances. • Parallax is the effect of noting you can discern the distance to an object if you can measure how much it appears to move around as you do.

8. Overall design calls for a “bootstrap” approach. • We start with small distances we can effectively measure with a ruler. • Next step in the design is to figure out that the “parallax” can tell us distances. • Parallax is the effect of noting you can discern the distance to an object if you can measure how much it appears to move around as you do.

9. Parallax Demo • Take a piece of paper and draw a stripe on it. • Hold the paper at arm’s length with your nose pointed at the stripe. • Hold 1 finger a 1 - 1.5 feet in front of your nose • Then close your left eye. Then open it and close your right eye. Notice how much your finger appears to move RELATIVE to the stripe. • Move finger until it is almost touching the stripe and try again. • Won’t be much apparent motion relative to stripe.

10. The effect is caused by moving your vision relative to your finger and you have accomplished the “motion” by using different eyes. • Same as using one eye and moving it the distance between you two eyes perpendicular to the line-of-sight. • How far can we determine distances that way? Need to answer: • (1) How far apart are our eyes ? • (2) How small a change in apparent motion can we measure?

11. OK now what, cont. • My eyes are separated by about 7 cm, and I know also I can see an angular separation of about 1 arc minute. So the diagram I draw is like this: Using trigonometry, d*sin(1.0 arc min) = 3.5 cm or d = 120 meters “tops,” q = 1 arc min. l about = d, s = 3.5 cm Apparent motion Each right triangle has a base of 3.5 cm and the apex angle of 1 arc minutes q d l s eyes

12. Parallax cont. • => If we know s and q we can calculate d (and or l). This give us the distance. A person’s distance or depth perception via binocular vision” is about 7 times worse than what I’ve calculated = about 50-60 feet (15-18 meters) . (cf., http://online.sfsu.edu/~psych200/unit6/66.htm) • Where did I go wrong? (a) Our eye needs a reference frame and the reference frame should be distant enough not to show parallax; (b) the eye doesn’t have the luxury of being able to accumulate data for hours and to look at objects with extremely well defined centers.

13. Parallax and astronomy • Need equivalent of “s” to be as large as possible and accurately measured. => • Here to Chicago won’t “do it.” • One side of earth to the other can allow us a low tech way of measuring the distance to the Moon. • Fine, but the closest star besides the sun is four million times further away. We need a larger “s.” This is

14. Parallax and astronomy • The Earth’s orbit around the sun! • Our most accurate measure now is by? Radar! And 1 arc second for q in our diagram with the earth’s motion around the sun to define s, we find that 1 arc second gives a distance called a Parsec (for parallax and arc second!)

15. The parsec Taking s = 1.50 x 1013 cm and q = 1 arc second and sin(1 arc second) = 4.85 x 10-6. Or, d = (1.50 x1013)/(4.85 x 10-6) = 3.09 x 1018 cm! Or in round numbers, 3 x 1018 cm = 1 par sec. A year = p x 107 sec of time=> p x 107 sec x 3 x 1010 cm/sec = 1018 cm, or 1 par sec = about 3 light years, where speed of light = c= 3 x 1010 cm/sec 1 parsec (pc) = 3 x 1018 cm 3 light years = 1 parsec

16. But will parallax work beyond the stars in our galaxy? • NO! => We need to determine parallax to a standard candle, if we can get it. • What do we need? Precise, small images, the better to find the centers of, and a well defined non-moving background for reference. • Stars are good for making small images, and distant stars or small galaxies are good for reference.

17. Limitations to parallax method • Swing around sun: Going to Pluto would get us a much larger swing, but the period is over 200 years! • Image quality; Rule of thumb is we can measure a center to about 1/10 of an object’s width. The best we could do on the ground a few years ago was 0.5 arc second images => about 20 pc distance. If can go into space can get a factor of 100 improvement without the blurring effects of the Earth’s atmosphere.

18. Limitations to parallax method • Swing around sun: Going to Pluto would get us a much larger swing, but the period is over 200 years! • Image quality; Rule of thumb is we can measure a center to about 1/10 of an object’s width. The best we could do on the ground a few years ago was 0.5 arc second images => about 20 pc distance. If can go into space can get a factor of 100 improvement without the blurring effects of the Earth’s atmosphere.

19. Hipparcos, the “ultimate solution” Hipparcos is an acronym for HIgh Precision PARallax COllecting Satellite. Appropriately the proununciation is also very close to Hipparchus, the name of a Greek astronomer who lived from 190 to 120 BCE. By measuring the position of the Moon against the stars, Hipparchus was able to determine the Moon's parallax and thus its distance from the Earth. He also made the first accurate star map which lead to the discovery, when compared with other data from his predecessors, that the Earth's poles rotate in the sky, a phenomenon referred to as the precession of the equinoxes. The concept of using the data recorded by the star mappers for astrometric and photometric observations was conceived by Erik Høg, a Danish astronomer involved with the Hipparcos mission. It was fitting that the catalogue which resulted from the star mappers should then be named after Tycho Brahe, a 16th century Danish astronomer, who produced the first 'modern' star catalogue (1602).

20. Hipparcos Instrument Main optic a mirror only 29 cm wide! For comparison, HST is over 200 cm wide. Being above atmosphere and having clever designs of a mask (think if knife edge test) to overcome the small mirror size so as to yield 100 times better star positions than could be done from the ground.

21. Hipparcos, the “ultimate solution” Scientists now possess, for the first time, a good three-dimensional picture of the bright stars in our neighbourhood. Hipparcos measured the distances of many stars, which were previously a matter of guesswork. For example Polaris, the Pole Star, is 430 light-years away. Hipparcos hit the headlines in 1997 when it showed that the chief measuring rod for the Universe was wrongly marked. Bright blue stars called Cepheids, of which Polaris is one, vary in luminosity in predictable ways. Astronomers use them to gauge distances of galaxies and the scale of the cosmos. But Hipparcos revealed them to be farther away than previously supposed. This made the Universe about 10 percent older. Also farther away than expected are the oldest known stars, the so- called halo stars. The change in distances cut their ages by a few billion years. Combined with the change in the cosmic scale, this solved a riddle in astronomy. Before Hipparcos the old stars seemed to predate the Universe. That was as nonsensical as mountains older than the Earth!

22. Bottom line we now have (1) a ruler measurement to the sun and astrometry to give us accurate positions to the (2) A satellite dedicated to the [boring, tedious] task of accurately measuring star positions to yield accurate (to the few percent level) the distances to “Cepheid Variables.” And Cepheid Variables are our closest standard candles and they are bright enough to be seen out to nearly 20 Mpc = where we can overlap with other things!

23. What are Cepheid Variables • Cepheids are unstable (on human time scales) stars with cycles of 1-50 days. And the longer the period the intrinsically more luminous they are =>

24. Fun animation on how standard candle works