Universe Exam 2

What subatomic particles were collided at LHC?

collides proton beams-the LHC was measuring the properties of the Higgs boson-and searching for the large family of new particles predicted by supersymmetric theories

Inertial frame of reference

is a reference frame in which an object stays either at rest or at a constant velocity unless another force acts upon it.

What is a wormhole? How can you increase the size of a wormhole?

is a theoretical passage through space-time that could create shortcuts for long journeys across the universe. Wormholes are predicted by the theory of general relativity. In order to stretch a wormhole you would need to inject dark matter.

What is Supersymmetry?

is a theory that links gravity with the other fundamental forces of nature by proposing a relationship between two basic classes of elementary particles: bosons, which have an integer-valued spin, and fermions, which have a half-integer spin.

What is Parallax? Explain.

is the way an object's position or direction seems to change depending on viewing angle.

Scientific Theory

-Explains previously observed phenomenon -Have experimentally testable prediction

Is it possible to travel to the future? Explain.

...Einstein's theory of special relativity, the passage of time is relative to an object's speed. The more quickly an object moves through space, the more slowly time passes for it compared to an observer traveling at a slower pace.

Neutron Star

A celestial object consisting of an extremely dense mass of neutrons, formed at the core of a supernova, where electrons and nuclei are compressed together so intensely by the force of gravity that protons and electrons merge together into neutrons.

What is the experimental piece of evidence for the existence of Dark Energy? Explain.

Accelerating expansion of the universe indicates that as the universe expands and more and more space is generated this expansion becomes faster and faster. It means that there is a property intrinsic to the space that acts against the gravity and causes the accelerating expansion if the universe. We call this "thing", the nature of which is still unknown to us, Dark Energy.

Is electron a fundamental particle? What about protons and neutrons? Explain.

An atom is not a fundamental particle, because it consists of protons and neutrons in its nucleus and has a cloud of electrons orbiting the nucleus...However, quarks and electrons cannot be broken apart and are fundamental particles. Protons and neutrons are also not fundamental particles, because they consist of quarks.

Why do call dark matter, dark?

Because dark matter does not interact with any particles that we know of.

Why can't wee see the state of the universe between Big Bang and thousands of years after that?

Because from Big Bang until thousands years after, the universe was in a plasma state, and plasma in opaque to light. So light from those epochs could not reach us.

According to SM, why is photon massless?

Because photon does not exchange any Higgs particles with the Higgs field, which means that it does not interact with the Higgs field and that's why it is massless.

Earth is spining with a rotational speed of 1656 km/h. why don't we feel this rotation?

Constant Rotational velocity-we are far away from the central rotation so we won't feel it. We have the same rotational velocity as the Earth.

What role does Cosmological Constant play in General Relativity and what does changing its value change?

Cosmological Constant determines the rate of expansion of the universe. A different value of the CC would result in a different rate of expansion which would lead to a universe that could not support life.

In Big Bang, the universe was extremely dense and hot and the emitted radiation must have been very high energy and short wavelength. So why does CMB have such a long wavelength? Explain.

Despite the fact that cosmic microwave background originated from the Big Bang and initially had very high energy and small wavelength, due to the expansion of the universe became more and more redshifted to microwave region.

Your friend says the inertia is a force that keeps things in their place, either at rest or in motion. Do you agree? Why or why not?

Disagree- Inertia is not a force. Objects tend to keep their state of rest or motion with a constant speed on a straight line, unless they are affected by unbalanced forces.

How does the frequency of a particular spectral line observed in sunlight compare with the frequency of that line observed from a source on Earth?

Due to Gravitational Redshift the emitted light and as a consequence the spectral lines from the elements in the sun are redshifted relative to their counterparts on the Earth.

We know that the Earth is rotating with a rotational speed of 1656 km/h. You are standing in front a wall but suddenly jump upward. If the Earth is rotating so fast, why doesn't the wall slam into you?

Due to inertia, when we jump we keep our tangential velocity, i.e. we move with the same sideway speed as the wall, so we will not slam into it.

Why is it impossible for objects with non-zero mass to get to the speed of light?

Due to relativistic mass increase, it is impossible for any object with non-zero mass to reach the speed of light. As the object's speed increases its mass increases, so more and more energy will be needed to accelerate it more. As the speed of the objects approaches the speed of light, infinite amount of energy will be needed to accelerate it further, which is unrealistic.

You wake up in a spaceship feeling being pushed down to the floor. What could be the possible causes?

Due to the principle of Equivalence, which states that the effects of gravity and acceleration are equivalent, it could be due to either gravity of a nearby object or the upward acceleration of the spaceship.

James Maxwell's theory of electromagnetism predicted that the speed of light is constant and does not depend on the speed of the source or the observer. What experiment proved this? Explain the experiment.

Fizeau experiment-to measure the relative speeds of light in moving water-Fizeau used a special interferometer arrangement to measure the effect of movement of a medium upon the speed of light.

How did Max Planck resolve the problem of Ultraviolet Catastrophe?

He realized that thermal energy is not radiated continuously, and is rather emitted in discrete packets of energy, which are called photons. This quantization of energy solved the UV catastrophe.

We learned that the Higgs Boson is the center piece of Standard Model. What role does Higgs field play in SM?

Higgs particle is the particle, through exchange of which with the Higgs field, other subatomic particles gain mass. Higgs field is a field that permeates the whole universe. When another particle interacts with Higgs field by exchanging Higgs particle they gain mass.

What are the pieces of the evidence that support the idea of expanding universe? Explain.

Hubble and his contemporaries observed that the spectral line of elements in other stars are systematically redshifted compared to the spectral lines of the same elements on the Earth. This cosmological redshift indicated that those galaxies were moving away from us. In addition, they discovered that the further a galaxy is from us, the more redshifted the signal is, which was a clear indication of an expanding universe.

What is the condition for a star to become a Black hole after its death?

If neutron degeneracy is not enough to resist the star's collapse it will continue to shrink until the matter is all compressed into an infinitely small, infinitely dense point called a singularity. This is the centre of a black hole.

How does double slit experiment reveal the particle-wave duality of particles such as electron and photon?

If pass two waves from two slits they will interfere with each other and will make an interference pattern on the screen. However, we see that we get this interference pattern when we do the experiment with the electrons, which were supposed to be solely particles. More specifically, in double-slit experiment we observe that even when we do the experiment with one electron at a time, we eventually get the interference pattern after shooting many electrons. This simply means that electrons act like particles at the source and when they hit the screen, but they inevitably act like waves while passing through the slits and each electron interferes with itself.

How does the idea of expanding universe contradict the idea of an eternal universe?

If the universe is expanding, it means that it must have originated from a beginning and could not possibly have existed forever.

Name three questions that are not answered by SM?

It does not explain the nature of dark matter and the nature of dark energy. It does not incorporate gravity and cannot explain why gravity is so weak compared to other forces of nature.

How is it possible for light path to be bent by gravity, while photon is massless and according to Newtonian Gravity shouldn't feel any gravity at all? Explain.

Light is not bent because of the gravitational force it experiences. Rather, gravity of objects curves the space around them and since light travels in this curved space, its path ends up being bent.

Which theory was the discovered Higgs particle in favor of: SUSY or Multiverse?

Neither. SUSY predicted a mass of 115 Gev for the Higgs particle and the theory of Multiverse predicted a mass of 140 Gev. The actual discovered mass was 125 Gev, which was none of the above predictions.

You are in a windowless train, which could be moving with constant speed or standing still. How can tell them apart using a pendulum?

No, there are no experiments that could distinguish two inertial frames of reference from one another. If you made the pendulum move- it would keep moving whether or not the train was still or moving at a constant speed. There is no point of reference for it.

Is space absolute in Newtonian Mechanics? (in the sense that time is universal and absolute)

No. Take the example of a ball thrown on a train, going with a constant velocity. The ball's path would look like a straight line to the person inside the train, while it would look like a parabola (curve) with respective to someone standing on the ground.

Are our current models able to predict the right value for the Cosmological Constant?

No. They fail miserably in predicting the correct value for the CC, which indicate that there are fundamental flaws in our current understanding of the universe.

Is it correct to claim that according to SR everyone's clock in the universe is different than everyone else's ? Explain?

No. two people will experience different times only and only if they move relative to one another. Any two observers in a same frame of reference that are stationary relative to one another will experience the same time.

What keeps the Earth moving around the Sun?

Nothing is necessary to keep the earth moving-The sun keeps it from following the straight-line path it would take if no forces acted, but it doesn't keep it moving

Inertia- A space probe may be carried by a rocket into outer space. What keeps the probe moving after the rocket no longer pushes it?

Nothing is needed to keep the rocket moving in outer space. If there is no friction and resistive forces present, which is the case in outer space, the rocket will continue its motion forever.

Can you think of a situation that a son or daughter becomes older than his or her parents?

Parents travel to space in a high speed rocket while son or daughter stays on Earth and ages older while the parents experience time slower. Two different inertial frames Twin Paradox.

What Quantum Mechanical effect prevents the gravitational collapse of neutron stars of mass less than three stellar mass?

Pauli's Exclusion Principle states that no two fermions can occupy the same quantum state. Neutrons are fermions, so they do not want to be close to one another. The repulsion between neutrons that stems from Pauli's Exclusion Principle works against the gravitational collapse of the neutron star.

According to Standard Model, why is photon massless?

Photons can travel in the speed of light c because of this property (being massless) - rest mass

Consider a ball at rest in the middle of a toy wagon, when the wagon is pulled forward, the ball rolls against the back of the wagon- interpret this observation in terms of Newton's first law.

Since the ball is initially at rest, it wants to keeps its state of rest due to inertia. So it will not immediately start to move with the wagon, while the wagons is moving forward. Eventually the ball will hit the wagon wall and be pushed forward.

You are inside a windowless room. You observe that a hockey puck which is on a frictionless surface, goes on a circle without any force acting on it. Does this violate Newton's Second Law?

Since the hockey puck accelerates without any force acting on it, it means that we are in a non- inertial frame of reference and our frame of reference is rotating which results in hockey puck going around a circle.

How do scientists determine the elements in distant stars? Explain.

Spectroscopy can be very useful in helping scientists understand how an object like a black hole, neutron star, or active galaxy produces light, how fast it is moving, and what elements it is composed of.

What does the hypothesis of Fine Tuning advocate?

The Fine Tuning hypothesis hypothesizes that the physical parameters including the Cosmological Constant have been fine-tuned to lead to a universe that could support condition for life to emerge.

Supernova

The brilliant point of light is the explosion of a star that has reached the end of its life

General Relativity

The central idea of general relativity is that space and time are two aspects of spacetime. Spacetime is curved when there is gravity, matter, energy, and momentum.

Name the force-carrying particles for the EM force, Weak force and the Strong force.

The force carrier particles that mediate the electromagnetic, weak, and strong interactions are called gauge bosons.

Imagine an astronaut falling into a black hole. In his perspective time is passing normally and he passes the even horizon. In our perspective, however, his clock completely stops at the event horizon and we never "see" him crossing the event horizon. How do you solve this apparent paradox?

There is no paradox here. In the astronaut's frame of reference, she passes the event horizon without feeling anything different. However, from an outside observer's perspective, light coming from her is so redshifted that she becomes unobservable. So, from an outside observer's perspective, as she approaches the event horizon she will appear to become redder and eventually disappear.

Light travels a certain distance in, say, 20000 years. How is it possible that an astronaut, traveling slower than light, could go as far in 20 years of her life as light travels in 20000 years?

This would be possible if the astronaut travels with speeds close to the speed of light. When the astronaut travels with speeds comparable to the speed of light, due to the relativistic time dilation, Earth's 20000 years will be equivalent to only a few years in her clock. So she can travel 2000 light years in much less time in her own clock.

What Quarks and Leptons are needed to build the elements of the Periodic Table?

Up and down combine together by Strong force through the exchange of gluons to form protons and neutrons. (refer to the lecture notes for the specifics of these combinations). Protons and neutrons form the nucleus, which combines with electrons through electric force to form different elements' atoms.

How have physicists learned of existence of dark matter?

We have observed its gravitational effects. Earth is at the edge of one of the arms of Milky Way, which is a spiral galaxy and is rotating around the center of the galaxy. This rotation requires a centripetal force which comes from the attractive gravitational force of all the matter in the Milly Way. But when we do the math, we realize that there is not enough matter to generate the required force. But the force is there, because we are rotating the Milky Way without a problem. So the only remaining possibility is that there is some form of matter in the galaxy that has gravity but is not observable by us and does not interact with ordinary matter known to us.

Non-inertial frame of reference

When a body does not seem to be acting in accordance with inertia or accelerating

Can we put as many photons as we want inside a tiny box?

Yes. Photons are bosons and Exclusion Principle does not apply to them.

Cosmological red shift

a shift toward longer wavelengths of the spectral lines emitted by a celestial object that is caused by the object moving away from the earth

Geocentric

measured from or considered in relation to the center of the earth

Heliocentric

measured from or considered in relation to the center of the sun

What is Hubble's law?

that galaxies move away from each other, and that the velocity with which they recede is proportional to their distance. It leads to the picture of an expanding universe and, by extrapolating back in time, to the Big Bang theory.

Special Relativity

the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.

Gravitational red shift

the process by which electromagnetic radiation originating from a source that is in a gravitational field is reduced in frequency, or redshifted, when observed in a region at a higher gravitational potential.

What is Spaghetification? and does it occur in all kinds of black holes?

the theoretical stretching of an object as it encounters extreme differences in gravitational forces like near a black hole