Questions and Answers

Questions and Answers:

Q: Why do astronomers talk about looking back into time?

A: Light travels very fast, but not infinitely fast.  Therefore, all of the light that we receive on Earth from outer space took some time to get here from wherever it originated.  The farther away it originated, the longer it took to get here.  So for distant objects, we see light that was emitted a long time ago, and therefore, see the object as it existed then.

Q: How do you know that dark matter exists?

A: Dark matter cannot be seen directly because it doesn't give off or absorb light, but we know it is there because it interacts gravitationally with the matter that we can see, and we see those effects.  From observing how galaxies rotate, how they move among other galaxies, what happens when clusters of galaxies pass through each other, and the growth of structures over the history of the Universe, we know that there must be much more matter than that which we can see directly, and it must be fundamentally different.

Q: What is dark matter?

A: So far, we don't know.  Current leading theories maintain that the dark matter mostly consists of small, neutral particles that have not yet been created in particle physics collider experiments.  We may soon detect such dark matter particles in laboratories on Earth, including in the SuperCDMS experiment.

Q: How do you know that dark energy exists?

A: Dark energy is accelerating the expansion of the Universe, and by measuring the growth of structure and the distances to very far objects, we know that the Universe's expansion has been accelerating lately.

Q: What is dark energy?

A: So far, we don't know.  Many people believe that dark energy may be the so-called a cosmological constant that is uniform throughout space and time, and may result from the vaccum fluctuations predicted by quantum mechanics.  However, this is only a hypothesis at this point.  It is the goal of several KIPAC projects to better understand dark energy.

Q: What is a black hole?  What is it like inside a black hole?

A: A black hole is a region of such high gravity that not even light can escape.  Outside of what is called the event horizon, a region surrounding the black hole, it acts like any other large mass which objects can orbit.  Inside the event horizon, all objects and light must fall to the center.  We do not currently know what happens at the center.

Q: How does a black hole form?

A: When a lot of matter collapses into a small space, it can become so dense that a black hole forms.  This can happen when a giant star collapses at the end of its life, or if a lot of material is thrown together relatively early in the Universe.

Q: If Gravity is the weakest of the four "forces of nature" and we can observe black holes, is it plausible that the other three forces of nature can result in their own variation of a black hole?

A: Gravity is a different force compared to the other three (electromagnetic, weak and strong) forces. The latter three are described by quantum field theories and do not have an analog to a black hole.

A black hole is produced when a high mass is concentrated in a very small space so that its gravity deforms space time so much that nothing can escape from it. The other three forces do not act on space time so they can not form a black hole.

Q:  In E=MC2 how does the speed of light influence the conversion of matter into energy? what property of light causes this? On the surface it seems random, but obviously it's not.  Why, when discussing the mass of the Higgs Boson, is the energy used instead instead of the mass? Is it because the units are less awkward?

A:  In the physics world, we often express a mass of particle in terms of the equivalent energy, just as you guessed - via E = mc^2.  This is just for convenience, as not to have all those incredibly small numbers (if expressed in grams...).  The two are interchangeable.

Q:  How do we know the age of the universe? Isn't it possible that there exists light that's so far away, that it hasn't gotten here yet?

A:  We can estimate the age of the universe from several measurements:
1) From measuring the current temperature of the microwave background light which is 2.7 K. We know that this radiation was emitted about 300000 years after the big bang (from theory) and what its temperature was at that time. Now if we assume an expansion rate of the Universe we can calculate the cooling time of the radiation to the current value. The expansion rate of the universe can be derived from supernova explosion measurements in distant galaxies. This gives a good estimate of the age of the universe.

2) From finding far away galaxies. This is indeed only a lower limit for the age of the universe.

3) Measuring the age of stars. This is usually done by looking at many stars in star clusters and results as well in a lower limit of the age of the universe.

Q: If our galaxy was on the edge of what we can currently see as the visible universe, would we be able to see 13.5 billion more lightyears further than we can at our current location? And if so does that support the Big Bang theory? 

A:That is a very interesting question. Indeed an observer which is at the edge of our observable universe could see the same distance further. However, he would see parts which we can see and some parts which are not seen by us. His observable universe is formed by his light cone, that means he can observe everything in the distance d=c*t where c is the speed of light and t is the age of the universe. Since he is at the edge of our observable universe he can see our position but in addition he can see other parts in the same distance which are to distant from us to be visible from earth. This can be visualized by drawing two circles of the same radius where the center of one circle is at the radius of the other circle. Everything inside the circle can be seen by an observer in the center and the circles have a large overlap but there is although a significant region only visible to one of the two observers.

Your second question is not so easy to answer in principle the Big Bang theory is compatible with this but it is not really a support for it. The best support for the Big Bang theory is the abundance of the light elements created in the Big Bag nucleosynthesis which is measured with great precision and compatible with the predictions of the Big Bang theory. Further support comes from the microwave background radiation which is caused by an expanding Universe as predicted by the Big Bang theory.

Q: How can, according to Newton's Conservation of energy, antimatter and matter, when they interact, annihilate each other?  Does the energy just transfer to another vessel or is the matter and antimatter truly destroyed? And a far fetched question; is it practical to use some form of energy to compress atoms enough to make them split and expose their inner workings while keeping them trapped in an electric barrier rather than using a particle accelerator?  

A: Matter and antimatter indeed annihilate into other energy forms. For example an electron and a positron can annihilate into two photons which takes the energy of the original particles.

Q: If a particle has the rest mass energy of a planck mass or more does it mean that particle must be a black hole or collapse into a black hole?

A: The Planck mass and length are defined by the density at which a massive particle would become a black hole according to classical general relativity.  However, at such small scales we know that quantum mechanics is also important, so classical general relativity does not give the correct answer. We did not succeed yet to formulate a unified theory which describes all forces in the same formalism. Such a theory would be needed to make consistent predictions about the properties of particles which enter the regime where the different forces have similar impacts on the behavior of the particle. So we really do not know what happens with a particle that reaches the Planck mass.