tests of the equivalence principle · 2016-07-27 · eöt-wash gravity workshop for the american...
Post on 25-Apr-2020
0 Views
Preview:
TRANSCRIPT
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
1
Tests of theEquivalence
PrincipleStephan Schlamminger
with Todd Wagner, Ki-Young Choi, Jens Gundlach and Eric AdelbergerFriday 1/5/2007
AAPT-Visit
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
2
Outline• What is the Equivalence Principle?
• Why do we want to test it?
• How has it been tested?
• The principle of our Apparatus
• What will you see in the lab tour?
• Results
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
3
The Equivalence Principle
Our Current theory of gravity, General Relativity,is based on the Equivalence Principle:
All bodies fall in a gravitational field with the same acceleration regardless of their mass or internal structure.
Einstein realized, that:
A uniform gravitational field is the same as an accelerated reference frame.
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
4
-a
F=-ma
The Equivalence Principle
g
F=mg
Gravitational field g Acceleration a
Inertial mass = gravitational mass, mI=mG for all bodies
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
5
General Relativity and the EPThree classical tests:ØPerihelion shift of MercuryØDeflection of light by the SunØGravitational red shift of light
The last two can be explained and calculated with the EP alone!
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
6
MotivationGR is one of the most essential pillars of modern physics.Ø We should continue to test it.
GR should be combined with quantum mechanics for a full description of Nature.
Ø New theories like string theory, quantum gravity, etc., most of which violate the equivalence principle at small level
Tests like this can be used to find new interactions (“fifth force”)
Tests of the equivalence principle are the most
sensitive probes of fundamental physics.
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
7
Historical overview
Galileo
Newton
Bessel
Potter
EötvösDicke
BraginskyUW
)( 2121
21
aaaa
+−
=η
drop
pendula
Type of experiment
torsionbalance
modulatedtorsionbalance
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
8
1st Tests of the Equivalence Principle
gmF G=
gmma
I
G=
gmma
I
G=
a2a1
gmm
ht
I
G
2=
gmma
I
G=amF I=
h
Time t to fall from h:
1600 Galileo: 1.0)( 212
121 ≈
+−
=aa
aaη
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
9
2nd Generation Tests
G
I
mm
gLT π2=l
Measurement of the swing periods of pendula:
Newton (1686), Bessel (183), Porter (1923)
5102 −≈ xη
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
10
Eötvös Experiments
θω cos2rmF II =
ω
θ
ε
r
)2sin(2
2
θω
εgr
mm
G
I=gmF GG =
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
11
Why a torsion balance?• A violation of the EP would yield to different plumb-line for different materials.
•A torsion balance can be used to measure the difference in plumb-lines:
Torsion fiber hangs like the average plumb line.
Difference in plumb lines produces a torque on the beam.
Eötvös (1922) 9105 −≈ xη
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
12 Principle of our Experiment
Source Mass
EP-Violating signal
Composition dipole pendulum(Be-Ti)
Rotation1 rev./ 20min
Autocollimator (=optical readout)
1020 - ∞1011 - ∞106 - 107
1 - 104
λ (m)source mass
Milky Way (incl. DM)Sunentire earthlocal masses (hill)
aBe
aTi
13.3min
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
13
20 µm diameter tungsten fiber(length: 108 cm)
tuning screws for adjustingtiny asymmetries
8 test masses (4 Be & 4 Ti )4.84 g each (within 0.1 mg)
5 cm
4 mirrors
EP Torsion Pendulum
frequency: 1.261 mHzquality factor: 4000decay time: 11d 6.5 hrsmachining tolerance: 5 µmtotal mass : 70 g
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
14 The Apparatus
upper part of the apparatus
on a concrete bridge (not shown)
turntable on air bearing& angle encoder
electrical feedthrough
thermal legs to adjust tilt
rotating adapter pieces
lower part of theapparatus
fiber positioner (x,y,z,φ)rotating vacuum vessel
autocollimatorion pump
(10-5 Pa)
thermal & magnetic shield(non rotating)
pendulummagnetic shield (rotating)
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
15 The Upper Part of the Apparatus
thermal expansion feet
to level turntable
air bearing turntable
electronics of angle encoder
feedthrough for electric signals
thermal insulation
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
16 The Lower Part of the Apparatus
vacuum chamber
ion pump
autocollimator
support structure forgravity gradient compensators
gravity gradient compensators
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
17
Systematic Effects
0.3 × 10 -13Tilt
0.3 × 10 -13Magnetic
0.9 × 10 -13Gravitational Coupling
1.7 × 10 -13Temperature
2.2 × 10 -13Total Systematic
3.6 × 10 -13Statistical Uncertainty
0.6 × 10 -13Turntable Rate
(cm/s2)
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
18
Range of a hypothetical “fifth” force (m)
Stre
ngth
rel
ativ
e to
gra
vity
ResultsExcluded
with
95 % confidence
Eöt-Wash Gravity Workshop for the American Association of Physics Teacher Meeting in Seattle 2007
19
THE END
top related