1,353 reputation
925
bio website ericmenze.com
location Minneapolis, MN
age 30
visits member for 3 years, 2 months
seen Jun 27 at 4:45

I'm a Computer (Web) Programmer/Analyst based in Anchorage, AK and Minneapolis, MN. I use (among other things) ASP.NET, C# and SQL Server.

I build things. Bicycles, computers, websites, guitars, cars, motorcycles, sound sytems... lots of things.


Jan
20
comment Would cosmological redshift be present in the following situation?
That last part confused me more. Which is it? If it is actually a property of expansion of space, then why wouldn't the situation pictured above experience redshifted planetary light?
Jan
20
comment Would cosmological redshift be present in the following situation?
Ah - so if we knew true velocities, the entire redshift would be simply due to relativistic doppler effects using said true velocity? I think that answers my question.
Jan
20
comment Would cosmological redshift be present in the following situation?
Why is it initially blueshifted?
Jan
20
comment Would cosmological redshift be present in the following situation?
I guess the fundamental part I'm asking is whether or not the cosmological redshift happens as the light travels through expanding space, or just due to observer velocities, peculiar or proper.
Jan
20
comment Would cosmological redshift be present in the following situation?
But... the universe HAS expanded (even if the planets have not receded), and thus $a(t_0)$ would be != 1, and thus redshift, would it not? Let's say they're REALLY far apart, and the universe has doubled in size since the light was emitted from one planet. Would that not mean $\frac {\lambda} {\lambda_0} = \frac {1} {2} $ ?
Jan
20
comment Would cosmological redshift be present in the following situation?
Why would they have 'peculiar velocity' toward each other, if they are at rest to each other? By the definition of peculiar velocity in the wiki article, would that not mean a peculiar velocity of $0\ m/s$?
Jan
20
comment Would cosmological redshift be present in the following situation?
So according to this, then, the planets would see redshifted light, as the energy density of the space between the planets has diminished from the expansion of the space between them. So - the planets would see somewhat redshifted light from the other?
Jan
20
comment Would cosmological redshift be present in the following situation?
And or the main point, why distinguish between peculiar and non-peculiar velocities, then, and have some distinction between 'doppler redshift' and 'cosmological redshift'? Why not just consider the vector sum of the two velocities as the doppler effect redshift?
Jan
20
comment Would cosmological redshift be present in the following situation?
A green line drawn on top of an image of two galaxies in Paint.NET? Thanks :)
Jan
20
comment Would cosmological redshift be present in the following situation?
As far as "forget about energy conservation in general relativity", for the example above let's say I pick the reference frame in which both planets are stationary. Within that reference frame, would I not have energy conservation and thus non-redshifted photons?
Jan
20
asked Would cosmological redshift be present in the following situation?
Jan
17
comment What would happen to matter if it was squeezed indefinitely?
Why would isothermal compression be a valid interpretation of the question? Performing an infinite amount of work on the substance has the potential to raise the temperature an infinite amount, and indeed without some magical heat sink, the temperature would rise and the substance would take a more or less positive slope through the phase diagram (though it may not be linear). Thus with enough force compressing (and heating) the substance, a vast majority of substances will transition through a gas and a plasma on their way to electron degeneracy, and ultimately a black hole.
Jan
14
comment Rocket Propulsion, delta V, acceleration and time. How do they relate?
Delta V goes up. Let's examine the same rocket, 4,000kg empty, 8,000kg fully fueled, and now let's strap on another 8,000kg bolt-on fuel tank that is magically 100% burnable fuel. You now have $ \Delta V = v_e * ln ( \frac {m_0} {m_1} ) = 4.0 km/s * ln ( \frac {16,000 kg} { 4,000 kg } ) = 4.0 km/s * ln (4) = 4.0 km/s * 1.386 = 5.545 km/s = 5,545 m/s $ In this example the fuel was 3/4 the total mass, where in the previous example it was 1/2, and that extra 1/4 gives us just twice the $ \Delta V $ (when you think about it, 3/4 could be used as two maneuvers of 1/2 the craft mass in fuel each).
Jan
14
awarded  Good Answer
Jan
14
revised What would happen to matter if it was squeezed indefinitely?
added 222 characters in body
Jan
13
comment Rocket Propulsion, delta V, acceleration and time. How do they relate?
A good read to get a better understanding of this is xkcd's rocket golf: what-if.xkcd.com/85 . What's important to note is that the only way to change your velocity (accelerate) is to throw/push/explode/golf something the opposite way. The speed at which it leaves you is $I_{sp}$, quantity of mass you hit/move/throw/burn per second is your flow rate - in my example above, 4,000kg of fuel was used in 10s, so 400kg/s was the burn rate.
Jan
13
comment Rocket Propulsion, delta V, acceleration and time. How do they relate?
I caveat the above comment to say that there are likely counterexamples to all of those, methods by which solid rockets can be throttled, bi-propellant setups that cannot be, etc. Estes model rocket engines are examples of full thrust 'til empty.
Jan
13
comment Rocket Propulsion, delta V, acceleration and time. How do they relate?
Well I doubt 'throttle' would be the appropriate name for them (they don't 'have' throttles), but yes they have mechanisms by which they can throttle (verb) their thrust. For example, liquid bi-propellant uses pumps to mix fuel with liquid oxygen, and by varying the flow rate they regulate thrust - the SSME is engaged at low thrust during solid rocket boosting for example. In hybrid rockets, they can regulate gas flow rates, whereas some solid propellant rockets (like boosters) have no method of regulating thrust or reignition - they're full blast until out of fuel.
Jan
13
awarded  Mortarboard
Jan
13
revised What would happen to matter if it was squeezed indefinitely?
added 201 characters in body