Recent comments in /f/askscience
[deleted] t1_j2arwb4 wrote
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[deleted] t1_j2arv5d wrote
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[deleted] t1_j2aqaxe wrote
Reply to comment by TychaBrahe in Before Newton, how did people explain falling apples? by maugustus
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forte2718 t1_j2apd17 wrote
Reply to comment by gravi-tea in has the speed of light always been constant? by 2bornnot2b
>The inflation in the first microseconds of universe that was faster than C refers only to space - not any of the matter or energy?
It refers to space, but that expansion of space also impacts the matter/energy occupying that space. This does mean that said matter/energy would have had a higher relative velocity than the speed of light ... however that is not an issue because the speed of light limit is a local law, meaning that two objects which are essentially adjacent to each other and capable of communicating causally must never have a relative velocity higher than the speed of light, and that local law is still respected by inflation. For objects which are separated by some distance and not capable of directly communicating or affecting each other causally during the period of inflation, there would be no actual way to measure or compare their relative speeds — any signals emitted by one object during inflation wouldn't be able to reach the other object until the period of inflation is over, since the distance between the signal and the distant object would also be increasing faster than light. Quoting from Wikipedia here:
>>In non-inertial frames of reference (gravitationally curved spacetime or accelerated reference frames), the local speed of light is constant and equal to c, but the speed of light along a trajectory of finite length can differ from c, depending on how distances and times are defined.[32]
This is essentially similar to how the law of conservation of energy is also a local law, meaning that localized, pointlike interactions must always conserve energy, but the total energy of a large volume (such as a region of expanding space) can still yield a change in the total energy within that volume.
>The expandsion of space that continues is only faster than C when added up over large distances?
Yes, that's correct. It's technically a misnomer to say that the rate of expansion is "faster than the speed of light" because the rate of expansion is not even a speed to begin with: it is a rate. It doesn't have the correct dimensions/units to be a speed, so comparing it to the speed of light is comparing apples to oranges. Speeds have units of distance/time, while the rate of expansion of the universe has units of 1/time (like Hertz), which is often more convenient to express as units of distance/time/distance (or a "speed per distance"). The Hubble parameter has a value of about 70 (km/s)/Mpc, which means that a galaxy which is 1 Megaparsec away will have a relative speed of approximately 70 km/s. But a galaxy which is 2 Mpc away will have a relative speed that is twice that (140 km/s), and so on. So the relative speed of an object is proportional to its distance in an expanding spacetime. The more distance that is between the two objects, the greater their relative speed will be. With enough distance between them, the relative speed is greater than that of the speed of light ... but then going back to point #1 above, relative speeds greater than the speed of light is only possible for objects with some substantial distance between them. Regardless of the Hubble parameter's actual value, the relative speed of two objects that are close-by always tends toward zero.
>Why do these theories assume the universe originating from a single tiny point? Would the math or evidence be much different if it had instead all originated from the size of a neutron or even a golf ball for example?
General relativity doesn't assume that the universe originated from a single tiny point, rather it derives this conclusion as a consequence of taking the universe's current state and applying the known laws of gravitational physics backwards deterministically to figure out what its past states must have been. When you take our expanding universe and work backwards, it becomes clear that any two distant objects must have been much closer in the far past ... and that if you go far enough into the past, the distance between them becomes arbitrarily small, reaching zero distance in a finite amount of time (elapsed in reverse).
The math/evidence wouldn't be substantially different, because if you work backwards and ask "how would the universe look if you work backwards in time from when it was the size of a neutron or a golf ball" the answer you get from general relativity is unequivocably "it would have been even smaller in the past, and if you go back just a little further into the past, the distance between all objects becomes exactly zero."
Now, it's worth pointing out that using general relativity to work backwards does result in it becoming non-predictive and giving nonsensical, almost certainly unphysical properties as you get closer and closer to that zero point. As you get that much closer, the universe's energy density also grows without bound, asymptotically approaching infinite density ... and we have very good theoretical reasons to expect that there are undiscovered physical processes in play that would have been very important for the universe's earliest dynamics — for example, corrections to general relativity due to any undiscovered quantum nature of gravity, which might prevent reaching a state where the universe is actually singular, with zero size and infinite density. But until we discover said processes/corrections, understand them, and reconcile them with general relativity's naive classical predictions, we won't be able to properly model the universe's behavior in such a state. So the best we can say at the present time is that general relativity seems to work reliably back far enough in time to where the universe was in an extremely condensed state, but prior to that point, we can't truly be certain just what the earliest moments of the universe were like. All we can say is that the observable universe at one time was in an extremely condensed high-density state, and it expanded from there into what it is today.
Hope that makes sense!
reerathered1 t1_j2ap205 wrote
Apples fall because they're ready to fall, and they're heavy. The glass fell because it was heavy, and it was on the edge of something and got shaken or pushed off. No further explanation needed in the minds of 99% of people. Feathers fall slowly because they're so light the air blows them around first. Things fall towards the ground because the ground is the stopping point for everything. Imagine if things fell towards the sky or the nearest tree. The world just wouldn't work. Therefore, they fall to the ground.
grayinsanity t1_j2aoyvc wrote
Reply to comment by YesWeHaveNoTomatoes in Could we scan the brain to diagnose conditions like autism and ADD? by okapi-forest-unicorn
Neuroimaging methods like MEG continue to advance and further aid clinical diagnosis of neurodevelopmental disorders including neurological diseases & ASD. We're pretty close y'all 😊
Ok-Development-8238 t1_j2annr5 wrote
Reply to comment by Navvana in Before Newton, how did people explain falling apples? by maugustus
The idea that something falling in a straight line/perpendicular to the earth is the same force that keeps the moon running parallel to it…still so surprising to me that someone (or multiple people) realized that
lollroller t1_j2aleaj wrote
Reply to comment by JanetYellenThrowAway in If collagen is a protein, and proteins are broken down during digestion, why would collagen or collagen supplements be beneficial? Is it just hype? by skepticated
Agree that these studies using collagen-derived small peptides do show multiple measures of clinical improvement, and that it is difficult to show collagen peptides in = collagen created = clinical improvement.
Ideally such trials would be controlled with similar small peptides but distinct from the amino acid content of the experimental peptides; and unfortunately the trials I’ve looked at so far are controlled with starch-based materials.
However, as much as I laughed at this topic 20 years ago, I’m slowly coming to the conclusion that there might be something here. More time will tell
[deleted] t1_j2aldiw wrote
Reply to comment by TychaBrahe in Before Newton, how did people explain falling apples? by maugustus
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[deleted] t1_j2aktuc wrote
Reply to thermal expansion affecting climate change? by mjoninha
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[deleted] t1_j2akq0r wrote
[deleted] t1_j2aklw7 wrote
Reply to comment by relativisticcobalt in Before Newton, how did people explain falling apples? by maugustus
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[deleted] t1_j2akfiy wrote
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OldWolf2 t1_j2ajhig wrote
Reply to comment by Navvana in Before Newton, how did people explain falling apples? by maugustus
I'd like to add that Newton and his contemporaries founded modern science -- the worldview that there is actually an objectively correct explanation for natural phenomena, and we can work on finding that out through thought and experimentation.
You will have noticed there are still many people today who don't hold that worldview, sadly; but in Newton's time and earlier, this described pretty much everyone outside of a select few, who were often considered heretics, witches, that sort of thing for their troubles .
Truth was what the church said it was and most people didn't have the concept of thinking about why apples fall, they just did. A large part of what Newton is remembered for is the notion of investigating this kind of thing at all .
(NB. My comment is Eurocentric like the question ; attitudes may have differed in other civilization centres ).
[deleted] t1_j2ajcqn wrote
Reply to comment by [deleted] in Before Newton, how did people explain falling apples? by maugustus
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[deleted] t1_j2aj5o5 wrote
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VoilaVoilaWashington t1_j2ahqjh wrote
Reply to comment by Nattekat in How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey
> Doesn't there have to be some reference frame whereby a body is not moving through space at all?
Relative to what? If you're measuring against the expansion of the universe, then you'd have to take VERY precise measurements against the most distant objects, and they're moving in all kinds of directions, but if you could, then sure, you could do that, somehow.
You'd just be moving at an insanely high velocity relative to anything local to you.
And because you're moving at that insane speed relative to, say, earth, you'd have to apply a massive force to actually get up to that insane speed.
> But if all speed is relative, both should see the other speed up, which feels paradoxical.
Welcome to relativity. Say you have 2 objects approaching Earth at 0.1c, relative to Earth. They'd see each other as moving less than 0.2c, because it's not additive, and if they could each see a clock on the other ship, they'd see that clock moving slower than their own.
[deleted] t1_j2ahq9v wrote
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RIPphonebattery t1_j2ah81c wrote
Reply to comment by amaurea in How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey
This makes perfect sense to me! I didn't realize speed was generally expressed with 1-sigma error bars, I'm most used to seeing 95% CI's.
Thanks for taking the time to reply
[deleted] t1_j2agyar wrote
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Worthyteach OP t1_j2agghn wrote
Reply to comment by jellyfixh in How old is the oldest bone that isn’t a fossil? Is there a limit for how long bones are preserved without becoming fossilised? by Worthyteach
I was wondering if the situation which would naturally preserve bones would end up causing fossilisation so if there is a limit in nature. Hadn’t thought of the amber angle, So potentially the tail of the dinosaur that was preserved in amber might still be bone?
DooDooSlinger t1_j2agerz wrote
Reply to comment by immwork in If collagen is a protein, and proteins are broken down during digestion, why would collagen or collagen supplements be beneficial? Is it just hype? by skepticated
It's unclear - the mechanism is far from understood. We get glycine from almost any protein source so that's definitely not it. But oligopeptides can definitely have hormonal effects so who knows, maybe degradation products of collagen exert hormonal effects which lead to increased synthesis. Obviously totally hypothetical
[deleted] t1_j2ag2gt wrote
Reply to thermal expansion affecting climate change? by mjoninha
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[deleted] t1_j2as20g wrote
Reply to comment by Macluawn in Before Newton, how did people explain falling apples? by maugustus
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