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Physics/Follow Up on Black Hole Collision Project


QUESTION: Dr. Nelson, Thank you so much for your help! I have begun to set up my experiment as per your directions, and I was wondering, is there a certain size that the fish tank needs to be in order for the experiment to be carried out successfully? Also as far as video data goes, how would I go about using the data gathered to prove something? I gather that the data could possibly be used to provide information about the magnitude of gravitational waves. How would I go about doing this?

ANSWER: There's really no set size.  Bigger is probably better/easier, but as long as the dimensions of the tank are large relative to the diameter of the tubes it should work...which can be a pretty small tank for thin-ish tubes.

Conversion of the data is something else again.  There are two levels, qualitative and quantitative.  First you should focus on getting a solid working experiment.  From there, you can see what level of detail is measurable in the pixels and frame rate of your video.  What would you be looking for?  Specifically, you would be looking for flow rates and density fluctuations.  That would be easiest to estimate directly if you had some kind of particles to track in the water.  Particles can be filtered out.  Small gelatin or similar (maybe somethign that won't dissolve like gelatin, but similar density) should work.  You'll want a distance indicator (ruler or something tiny but of well-known length) in the video to measure from.  It doesn't have to be big.  That gets you velocities and densities as a function of time.  From there we can go further.

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QUESTION: Earlier you had said something about introducing food coloring into the water, a different color for each tube. Would I be doing something similar with the particles? As in would I need to differentiate between the particles introduced on either side of the tank? Or would I simply be introducing the particles on one side and seeing where they travel?

ANSWER: Yes.  For qualitative behavior, food coloring can probably cover more of the tank and make more dramatic photos.  So you'll probably want to do both, it really won't take that long once you've built the system.  But you should go with different colored particles if you can, something that won't gum up your fish tank pump (or put a filter at the start of the pump).  Making measurements off of dye density is a lot trickier to quantify, however.  Even a qualitative experiment, being somewhat unique, might be useful in this case.  

I just went into my kitchen and put some pepper in a glass and poured water in.  Some particles floated, some sank, and some (which would be the appropriate ones to use), worked with chili powder as well.  A drop of soap really helped the floating ones come off the surface and float around in there.  These could be drizzled in from the top of the tank, possibly, and you might be able to adjust the temperature of the water to help them drift down to the middle of the tank...very carefully.

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QUESTION: Ok, that makes a lot of sense. I am beginning to write my research portion of the paper which, as I am sure you know, is due before the actual data of the experiment is. I was wondering if you could direct me towards what all I would need to cover in the research portion? I have started off with some basic background on black holes, i.e. what they are and how they function.
         Thank you once again,

Well, a research section is mostly up to you to find sources.  I'm not going to point you to Stephen Hawking's book widely known amongst physics grad students as "the Yellow Terror."  It's mathematically intractable.  I would start where everyone starts, google.  After that, I would turn to where researchers turn, JSTOR.  A search of "colliding black holes" returned 621 results, not all of them relevant or available.  Your school or local college may have better access than I do, now that my new job is not at a university.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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