Watching The Big Bang

Transcription

1 Watching The Big Bang Have Primordial Gravitational Waves Been Detected? Robert H. Gowdy Virginia Commonwealth University September 5, 2014 R. H. Gowdy (VCU) Cosmology 09/05 1 / 12

2 Summary Picturing the Expanding Universe Galaxies get farther apart without actually moving. There is no center and no edge (that we can see). A spacetime picture helps. Picturing the Big Bang "Fireball" It is all around us and almost the same temperature in all directions. It is actually the end of the Big Bang 380,000 years from time = 0. Its small temperature fluctuations are very sensitive to all aspects of a cosmological model. The Concordance Cosmological Model Inflation, dark matter, and dark energy are all assumed but not explained. Early gravitational waves polarize the Big Bang radiation. Different explanations for inflation predict different amounts of early gravitational waves and different amounts of polarization. The BICEP2 experiment measured a LOT of polarization. R. H. Gowdy (VCU) Cosmology 09/05 2 / 12

3 Doppler Effect versus Geometry Spectral lines from distant galaxies are shifted redward by an amount that is proportional to their distance from us. R. H. Gowdy (VCU) Cosmology 09/05 3 / 12

4 Doppler Effect versus Geometry Spectral lines from distant galaxies are shifted redward by an amount that is proportional to their distance from us. Perhaps the galaxies are moving away from us and the redshift is just the doppler shift. R. H. Gowdy (VCU) Cosmology 09/05 3 / 12

5 Doppler Effect versus Geometry Spectral lines from distant galaxies are shifted redward by an amount that is proportional to their distance from us. Perhaps the galaxies are moving away from us and the redshift is just the doppler shift. Or the galaxies are not moving but the geometry of spacetime is changing so that more distance appears between them. R. H. Gowdy (VCU) Cosmology 09/05 3 / 12

6 The Expansion is Conformal: Light ignores it Adjust the time coordinate so that the physical unit of time appears to shrink also. R. H. Gowdy (VCU) Cosmology 09/05 4 / 12

7 The Expansion is Conformal: Light ignores it Adjust the time coordinate so that the physical unit of time appears to shrink also. Light travels at 45 degrees to the vertical in this picture. R. H. Gowdy (VCU) Cosmology 09/05 4 / 12

8 The Expansion is Conformal: Light ignores it Adjust the time coordinate so that the physical unit of time appears to shrink also. Light travels at 45 degrees to the vertical in this picture. This spacetime is conformal to flat, unchanging Minkowski spacetime. R. H. Gowdy (VCU) Cosmology 09/05 4 / 12

9 The Expansion is Conformal: Light ignores it Adjust the time coordinate so that the physical unit of time appears to shrink also. Light travels at 45 degrees to the vertical in this picture. This spacetime is conformal to flat, unchanging Minkowski spacetime. Electromagnetism is conformally invariant, so it ignores the change. Massive particles do not, so lengths and times are affected. R. H. Gowdy (VCU) Cosmology 09/05 4 / 12

10 History of the Universe: Spacetime Here is the Big Bang in conformal coordinates. R. H. Gowdy (VCU) Cosmology 09/05 5 / 12

11 History of the Universe: Spacetime Here is the Big Bang in conformal coordinates. The early expansion amplifies sound waves with wavelengths comparable to the sound horizon size. R. H. Gowdy (VCU) Cosmology 09/05 5 / 12

12 History of the Universe: The View from Now - 1 The sound horizon size determines the size scale of the temperature fluctuations. R. H. Gowdy (VCU) Cosmology 09/05 6 / 12

13 History of the Universe: The View from Now - 1 The sound horizon size determines the size scale of the temperature fluctuations. The angular scale of the fluctuations depends on when "now" is. R. H. Gowdy (VCU) Cosmology 09/05 6 / 12

14 History of the Universe: The View from Now - 2 An extra dimension in the picture may help: R. H. Gowdy (VCU) Cosmology 09/05 7 / 12

15 History of the Universe: The View from Now - 2 An extra dimension in the picture may help: Here the circle is actually our view of the heavens: The Celestial Sphere. R. H. Gowdy (VCU) Cosmology 09/05 7 / 12

16 History of the Universe: The View from Now - 2 An extra dimension in the picture may help: Here the circle is actually our view of the heavens: The Celestial Sphere. The size spectrum of the fluctuations determines T now as well as other parameters of the cosmological model. R. H. Gowdy (VCU) Cosmology 09/05 7 / 12

17 The Universe s Baby Picture Here is a picture of the micowave background radiation temperature fluctuations on the Celestial Sphere. R. H. Gowdy (VCU) Cosmology 09/05 8 / 12

18 The Universe s Baby Picture Here is a picture of the micowave background radiation temperature fluctuations on the Celestial Sphere. Temperature = ± K. RMS fluctuations= 18 micro-k. R. H. Gowdy (VCU) Cosmology 09/05 8 / 12

19 The Universe s Baby Picture Here is a picture of the micowave background radiation temperature fluctuations on the Celestial Sphere. Temperature = ± K. RMS fluctuations= 18 micro-k. T now = ± billion years. R. H. Gowdy (VCU) Cosmology 09/05 8 / 12

20 The Concordance Big Bang Model R. H. Gowdy (VCU) Cosmology 09/05 9 / 12

21 The Polarization of the Cosmic Background: BICEP2 R. H. Gowdy (VCU) Cosmology 09/05 10 / 12

22 The Polarization of the Cosmic Background: BICEP2 Background Imaging of Cosmic Extragalactic Polarization R. H. Gowdy (VCU) Cosmology 09/05 10 / 12

23 BICEP2 Result The ratio r between the tensor mode polarization and the scalar mode polarization is r = with a confidence level of 68%. R. H. Gowdy (VCU) Cosmology 09/05 11 / 12

24 BICEP2 Result The ratio r between the tensor mode polarization and the scalar mode polarization is r = with a confidence level of 68%. But there is another result, from the Planck Space Observatory: r < 0.11 with a confidence level of 95%. R. H. Gowdy (VCU) Cosmology 09/05 11 / 12

25 BICEP2 Result The ratio r between the tensor mode polarization and the scalar mode polarization is r = with a confidence level of 68%. But there is another result, from the Planck Space Observatory: r < 0.11 with a confidence level of 95%. Now what? R. H. Gowdy (VCU) Cosmology 09/05 11 / 12

26 The Problem The BICEP2 result is consistent with the largest amount of primordial gravitational radiation that any inflation model can produce. It is evidence for inflation and actually constrains the model very tightly R. H. Gowdy (VCU) Cosmology 09/05 12 / 12

27 The Problem The BICEP2 result is consistent with the largest amount of primordial gravitational radiation that any inflation model can produce. It is evidence for inflation and actually constrains the model very tightly The Planck result is consistent with NO primordial gravitational radiation at all. R. H. Gowdy (VCU) Cosmology 09/05 12 / 12

28 The Problem The BICEP2 result is consistent with the largest amount of primordial gravitational radiation that any inflation model can produce. It is evidence for inflation and actually constrains the model very tightly The Planck result is consistent with NO primordial gravitational radiation at all. One suggestion is that the polarization detected by BICEP2 is the result of interstellar dust. R. H. Gowdy (VCU) Cosmology 09/05 12 / 12

29 The Problem The BICEP2 result is consistent with the largest amount of primordial gravitational radiation that any inflation model can produce. It is evidence for inflation and actually constrains the model very tightly The Planck result is consistent with NO primordial gravitational radiation at all. One suggestion is that the polarization detected by BICEP2 is the result of interstellar dust. Planck surveyed the background at several different frequencies and should be able to detect the effects of dust. R. H. Gowdy (VCU) Cosmology 09/05 12 / 12

30 The Problem The BICEP2 result is consistent with the largest amount of primordial gravitational radiation that any inflation model can produce. It is evidence for inflation and actually constrains the model very tightly The Planck result is consistent with NO primordial gravitational radiation at all. One suggestion is that the polarization detected by BICEP2 is the result of interstellar dust. Planck surveyed the background at several different frequencies and should be able to detect the effects of dust. There are some suggestions that the concordance model that is being used to intepret both BICEP2 and the Planck results is no longer working. R. H. Gowdy (VCU) Cosmology 09/05 12 / 12

31 The Problem The BICEP2 result is consistent with the largest amount of primordial gravitational radiation that any inflation model can produce. It is evidence for inflation and actually constrains the model very tightly The Planck result is consistent with NO primordial gravitational radiation at all. One suggestion is that the polarization detected by BICEP2 is the result of interstellar dust. Planck surveyed the background at several different frequencies and should be able to detect the effects of dust. There are some suggestions that the concordance model that is being used to intepret both BICEP2 and the Planck results is no longer working. Loud cheers from the theorists who pull new models out of their desk drawers in large numbers and publish them on the Arkiv. R. H. Gowdy (VCU) Cosmology 09/05 12 / 12