matter and dark energy are required, and that we don't know the origin of any of these mysteries. As long as you can measure the properties you’re seeking, you’ll be able to build a cosmic distance ladder, determining how the Universe has expanded between the time the light was emitted from your distant objects and when it arrived at your eyes.Ī detailed look at the Universe reveals that it's made of matter and not antimatter, that dark.

Then, you can measure properties of those galaxies or objects within those galaxies: rotation properties, velocity dispersions, surface brightness fluctuations, individual events like type Ia supernovae, etc. Because you know how these stars work, you can determine their distances, and therefore the distances to those galaxies.

you can look for them in distant galaxies. Once you know how far away those types of stars are - Cepheids, RR Lyrae, certain types of giant stars, etc. As the Earth moves around the Sun, that tiny change in distance is enough to reveal how much the stars shift by, the same way your thumb shifts relative to the background if you close one eye and then switch eyes. You can measure individual stars directly, determining their distance simply by measuring them throughout the year. Do this for enough objects at a variety of distances - including large enough distances - and you’ll reveal how quickly the Universe is expanding, with very small errors and uncertainties.Īt this point, there are many different ways of doing this. All you’re going to do is measure objects that you understand, determining both their distance from you and how much the light from them gets shifted by the expansion of the Universe. The distance ladder method is easier to understand. Each “step” carries along its own uncertainties, but with many independent methods, it's impossible for any one rung, like parallax or Cepheids or supernovae, to cause the entirety of the discrepancy we find. The construction of the cosmic distance ladder involves going from our Solar System to the stars to. How do we even get those rates? That’s what Lindsay Forbes (no relation) wants to know, asking: But one of cosmology’s biggest puzzles is that we have two completely different methods for measuring the Universe’s expansion rate, and they don’t agree. Similarly, if you know the expansion rate now and how it’s changing over time, you can go all the way forward to the heat death of the Universe. If you know the expansion rate now and what’s in your Universe, you can go all the way back to the Big Bang. Go backwards, and things will get denser, hotter, and less clumpy.

If everything is moving away from everything else, we can extrapolate in either direction to figure out both our past and our future. If you want to understand where our Universe came from and where it’s going, you need to measure how it’s expanding. Siegel / Damien George / / Planck Collaboration underlying these maps encodes a tremendous amount of information about the early Universe, including what it's made of and how quickly it's expanding.

We explore predictions against other surveys and experiment configurations, finding that wide patches with maximal sky overlap between CMB and LSS surveys are most powerful for σ 8 ( z ) and f NL.The hot and cold spots from the hemispheres of the sky, as they appear in the CMB. Our results also suggest that CMB lensing in combination with LSS photometric surveys is a competitive probe of the evolution of structure in the redshift range z ≃ 1 – 7, probing a regime that is not well tested observationally. Without CMB lensing, the precision always degrades by an order of magnitude or more, showing that a joint analysis is critical. Having no sky overlap between experiments degrades the precision of σ 8 ( z ) by a factor of 20, and that of f NL by a factor of 1.5 to 2. Assuming large sky overlap between CMB-S4 and LSST, we show that a joint analysis of CMB-S4 lensing and LSST clustering can yield very tight constraints on the matter amplitude σ 8 ( z ), halo bias, and f NL, competitive with the best stage IV experiment predictions, but using complementary methods, which may carry different and possibly lower systematics. This will enable use of sample variance cancellation techniques to determine cosmological parameters, and use of cross-correlation measurements to break parameter degeneracies. The lensing convergence measurable with future CMB surveys like CMB-S4 will be highly correlated with the clustering observed by deep photometric large scale structure (LSS) surveys such as the LSST, with cross-correlation coefficient as high as 95%.

Quicklens cmb