# Presentation: 470559

**Hidden Dimensions****,   ****	****Warped Gravity****,   ****	****Dark Energy**

**Eric Linder **
**UC Berkeley **
**Lawrence Berkeley National Laboratory**

## Uphill to the Universe

**Steep hills:**
**Building up -**
**Eroding away -  **

## Start Asking Why, and...

**There is no division between the human world and astrophysics. **

**...**

**...**

**Everything is dynamic, all the way to the expansion of the universe.**

## Mapping Our History

**The subtle slowing down and speeding up of the expansion, of distances with time: ****a(t)****, maps out cosmic history like tree rings map out the Earth’s climate history.**** **

- STScI

## Discovery!  Acceleration

**Exploding stars – ****supernovae**** – are bright beacons that allow us to measure precisely the expansion over the last 10 billion years.**** **

- data from Supernova Cosmology Project (LBL) ; similar data from Hi-Z Team
- graphic by Barnett, Linder, Perlmutter & Smoot (for OSTP)

## New Frontiers

**Beyond Einstein:**** What happens when gravity is no longer an attractive force?**

- Scientific American

**Discovery**** ****(****SCP,HiZ 1998****)****:**** 70% of the universe acts this way! **
***Fundamentally new physics.****** Astronomy is the key. ***

## What’s the Matter with Energy?

**They are off by a factor of **

**1,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000.**

**This is modestly called the**** ****fine tuning**** ****problem.**** **

**Why not just bring back the cosmological constant (********)?**** **
**When physicists calculate how big ******** should be, they don’t quite get it right. **

## Cosmic Coincidence

**Matter**

**Dark energy**

**Today**

**But it gets worse:**** Think of the energy in ******** as the level of the quantum “sea”.  At most times in history, matter is either drowned or dry. **

**Cosmic Coincidence**

## On Beyond !

**On beyond ********! It’s high time you were shown**
**That you really don’t know all there is to be known. **
**-- ****à**** la Dr. Seuss, *****On Beyond Zebra***
***We need to explore further frontiers***** in high energy physics, gravitation, and cosmology. **
**New quantum physics?**** ****	****	****	****      ****Energy of the vacuum (nothing weighs something)?**
**New gravitational physics? ****	****	****   ****Quantum gravity, supergravity, extra dimensions?**** **
**We need new ideas from physics and astrophysics (constrained by astronomy).**

## Hidden Dimensions

**Extra dimensions**** have been used for unification in physics since the 1920s. **
**String theory**** likes 6 or 7 (or 8) extra dimensions. **
**Why don’t we see them? **
**Either they’re very small (compact, tightly rolled), or large but we’re restricted to a 3D subset -- a (mem)****brane**** in a higher dimensional bulk.**
**Compact extra dimensions can be tested at high energies (or tabletop gravity experiments). **

## Hidden Dimensions

**They may also explain the weakness of gravity. **
**In ****4+N**** dimensions, Newton’s law is **
**    ****F = G****4+N****1+N/2 ****m****1****m****2****/R****2+N****	****	****	****	****(R<<r) **
**    ****F = [G****4+N****1+N/2 ****m****1****m****2****/r****N****]/R****2**** = [Gm****1****m****2****]/R****2**** ****	**** ****(R>>r)**
**So ****G = G****4+N****1+N/2 ****/ V****N****.  **
**For N=2, this solves the energy scale problem and predicts altered gravity on distances ****r < 1mm**** -- just what experiments are about to achieve! **

***Gravity?***

***Electro-magnetism?***

## Warped Gravity

**Large extra dimensions -- ****braneworlds**** -- are more interesting astronomically. **
**Spacetime is warped**** by e****-y**** as one moves a distance y off a brane. Think of the spacetime properties as an *****index of refraction*****: such a spatial gradient ********n**** localizes light (and the rest of physics). **
**This can solve energy scale problems: **
**	****Planck energy scale ****M****Pl**** = ********hc****5****/G = 10****28**** eV**** **
**	****Electroweak energy scale ~ ****1 TeV = 10****12**** eV**

**y**

## Warped Gravity

**On large (cosmological distances) there may be ****leaking gravity****.  The cosmic expansion would appear slower over these distances, i.e. accelerating today! **

**Like localized light in a fiber optic, gravity will eventually leak off into hidden dimensions. **
**Or think of a tuning fork: it radiates sound in all directions, but the waves are stronger if localized. **

## Gravity and Galaxies

**A new theory or a new component?**** **
**Inner solar system motions ******** ****General Relativity**** **
**Outer solar system motions ******** ****Pluto**
**Galaxy rotation curves ******** ****Dark Matter**** **
**[NB:**** even TeVeS “new MOND” does not fit clusters, ****	**** halo offset or flattening****]****	****	****	****	****	****	****[****plus it involves 3 new fields and 3-4 new parameters****]**
**Scalar-tensor gravity theories are faced with tests from solar system (Cassini ******** ******** ≈ 40000), stellar cooling, pulsars, primordial nucleosynthesis. **

## On Beyond !

**You’ll be sort of surprised what there is to be found Once you go beyond ******** and start poking around.**
**-- ****à**** la Dr. Seuss, *****On Beyond Zebra***
***We need to explore further frontiers***** in high energy physics, gravitation, and cosmology. **
**New quantum physics?**** ****	****	****	****      ****Energy of the vacuum (nothing weighs something)?**
**New gravitational physics? ****	****	****   ****Quantum gravity, supergravity, extra dimensions?**** **
**We need new, highly precise data**

## Astronomy is the Playing Field

**Can we detect dark energy in the lab?**
**No direct detection:**** ****	****	****	****	****	****	*****Dark energy in solar system = 3 hours of sunlight***
**Can look for hints in the**** ****lab and accelerator, like variations of fundamental constants (but better in universe), tabletop gravity experiments. **
**Solar system tests can give some constraints on new gravity.**
**The**** ****best laboratory for the New Physics is the universe.****  ****Astrophysics and cosmology will be the key playing fields.**** **

## Standard Candles

**Brightness tells us distance away (lookback time)**
**Redshift measured tells us expansion factor (average distance between galaxies)**

## What makes SN measurement special? Control of systematic uncertainties

*Images*

*Spectra*

*Redshift & SN Properties*

**data**

**analysis**

**physics**

**Nature of**
**Dark Energy**

**Each supernova is “sending” us a rich stream of information about itself.**

- What makes SN measurement special?** Control of systematic uncertainties**

- SCP, NERSC

## Design a Space Mission

**c****o****l****o****r****f****u****l**

- wide

**9000******** the Hubble Deep Field**
***plus***** 1/2 Million ******** HDF**

**deep**

**•**** ****Redshifts z=0-1.7 ****•**** Exploring the last   10 billion years ****	****•**** 70% of the age of the universe ****	**

**Both optical and infrared wavelengths to see thru dust.**

- NOAO: LBL CCD

## Astronomical Resources

**Astronomy: **
***Wide Field Imaging from Space***
- Dark Energy and Dark Matter 	Weak and Strong Lensing 		Large Scale Structure 		Clusters of Galaxies 		Quasars 				Galaxy Formation and Evolution 	Stellar Populations 			Galactic Structure 			Micro-Lensing 			   The ISM 				   The Solar System 			Supernovae 				   Star Formation

***widefield.lbl.gov***

## Gravitational Lensing

**“****Galaxy wallpaper”**

## Gravitational Lensing

**Lensing measures the mass of clusters of galaxies.  **
**By looking at lensing of sources at different distances (times), we measure the ****growth of mass****. **
**Clusters grow by swallowing more and more galaxies, more mass.**

**Acceleration *****- stretching space -***** shuts off growth****, by keeping galaxies apart. **
**So by measuring the growth history, lensing can detect the level of acceleration, the amount of ****dark energy****.**

## Exploring the Unknown

**Complementary probes give**** crosschecks, synergy, reduced influence of systematics,  *****robust answers*****.**
**Space observatory gives infrared and high redshift measurements, high resolution and lower systematics. **
**Wide field telescope gives multiple probes ****	****	****	****(e.g. SN Ia, Weak Lensing, Clusters, Strong Lensing, SN II) automatically, and ****rich astronomical resources****.**

**When you have a mystery ailment,**** ****	****	****	****you want a diagnosis with blood tests, EKG, MRI,...**

## Fate of the Universe

- Contemporary Physics Education Project (CPEP)

**UniverseAdventure.org**

## Frontiers of the Universe

**	****	****	****	****What is dark energy?**
**	****	****	****Will the universe expansion accelerate forever?**
**	****	****Does the vacuum decay? Phase transitions?**
**	****How many dimensions are there? **
**How are quantum physics and gravity unified? **
**What is the fate of the universe? **

**Uphill to the Universe!**

## Frontiers of the Universe

- Breakthrough of the Year

- 1919

**Cosmology holds the key to new physics in the next decade.**

- 1998

- 2003

**Let’s find out!**