Continuing with our cosmology series, this session will focus on one of the least understood concepts in astrophysics - Dark matter and Dark energy!
Date - August 08 (Sat), 2020
Time - 9.00pm IST
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Looking forward to seeing you there!
This thread will also be used to share resources related to session
Hereās the session recording.
Hello!
I ask below the questions which I was pondering after the session.
ā¦the above are some questions I had from listening to the discussion. I have some more questions that may dwell into realms of metaphysics, though I believe it may help me understand this concept (dark matter) better. Will wait for your reply and save these questions for the next discussion.
P.S. This is the first time I am actually participating in a discussion forum (usually a silent reader). So pardon for any errors if any in my questions and the way in which I may raise them.
Hy @Yoursprasanna , props for asking the questions!
Nope theyāre not related, the word ādarkā is the only commonality between the two things. The nodes are the places where dark matter is distributed according to our current models. There are currently no ways of determining where dark energy would be. We first need to answer āwhatā they are before we move on to āwhereā they are
Massive objects (made of normal matter) cause gravity lensing however these are accurately measurable. The difference in lensing supposed to be caused by normal matter and the observed lensing caused by normal matter+ dark matter is one of the way we know dark matter exists
Yes, they do. Everything about dark matter is measurable. Its mass, density, volume etc. The percentages pie chart which says ā27% dark matterā actually means dark matter fills up 27% of the universe by volume.
Thanks for the interesting questions and feel free to ask more questions or even create a new topic!
Thanks for the answers @kishan !!
Sorry for my late reply. Your answers were lucid.
My other questions were about the expansion of the universe and dark matter observation. As I mentioned earlier, both my questions are āhow-what-ifsā.
Using the analogy that, everything we observe is slowed down because of the vast distances of separation and finite speed of light. Like, even light from sun is supposed to be 8 minutes old. My question is, while observing and hypothesizing that boundary of observable universe is expanding (you had mentioned 45 billion light-years, if my memory serves correct) we are essentially speaking the boundary was expanding some 45 billion years ago. This instant, whilst I type, the boundary MAY have stopped expanding or even began crunching 
, right? So, how are we actually accept this theory of expanding universe? I understand the Doppler shifts and you can answer with that stand-point.
Second, you had mentioned an anomaly ( donāt know whether Iām using it right here) that the systems in the outer edge of a galaxy move faster than its inner regionsā¦ and this is an observation indicating presence of dark matter.
What if, the gravitational effect of the supermassive black-hole is yet to reach its outer rings to slowā em down ( I base this argument on the fact that gravitational waves propagate thru space and time, as was recently discovered, and so does the black holes effect, right?). This argument if true, should be observable.
In both my questions, I kind of think, information(light/EMR that we observe)is reaching us slow (by million of years), how are these observations accepted and used for developing theories?
That sums up my questions for now.
Thank you!
Please pardon, if the questions seem silly.