Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science

Submitted by AutoModerator t3_y24qed in askscience

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Physics, Astronomy, Earth and Planetary Science

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

Answering Questions:

Please only answer a posted question if you are an expert in the field. The full guidelines for posting responses in AskScience can be found here. In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for /r/AskScience.

If you would like to become a member of the AskScience panel, please refer to the information provided here.

Past AskAnythingWednesday posts can be found here. Ask away!

151

Comments

You must log in or register to comment.

Tri_Ban_Had t1_is0vu4e wrote

How does antenna coupling work, and what are the more severe effects? Do the whole and decimal multiplier of distance vs wavelength i.e. 5 vs 5.5 lengths of separation matter?

My understanding is the wave length matches the distance/antenna core correctly, within a given proximity to transfer a large amount of the incoming energy directly into the receiving antenna.

5

ContentDoor1704 t1_is1aod7 wrote

What are the most promising hypotheses for why galaxies rotate? What is the relevance of black holes?

5

Brickleberried t1_is1wsck wrote

> What are the most promising hypotheses for why galaxies rotate?

It's simply conservation of angular momentum. To steal from this article:

> Structures rotate because of a property known as angular momentum. Angular momentum is a measure of mass and rotation, and it is a conserved physical property. One of its characteristics is that when mass moves closer together, it spins faster to keep angular momentum constant. You see this in figure skaters when they leap into the air and pull their limbs close to their bodies. Galaxies, stars, and planets all formed from great clouds of cosmic gas and dust. As gravity caused these clouds to collapse, even the smallest bit of rotation was amplified. So it is natural that they all spin.

.

> What is the relevance of black holes?

Not relevant to galactic rotation.

5

fly-guy t1_is1f32n wrote

The Andromeda paradox. Alice is sitting and watching the Andromeda galaxy through a telescope. Bob is running toward Alice and is also watching the galaxy through his teleccope. Apparently Bob (moving in regard to Alice) is seeing the galaxy at a point of time which is ahead of what Alice sees (who is "stationary").

I know it can be calculated just howuchnis differs, but is it possible to explain it so I can understand the principle? Why does moving alter the view (timewise) through the telescope and what happens if the stationary Alice viewer starts moving and catches up with Bob while still looking through her telescope?

5

Rex_Mundi t1_is1feyr wrote

I was looking at the ancient city of Shangdu on Google Earth. I zoomed out and it kind of looks like it is on the edge of a huge ancient crater.

Is it?

https://www.google.com/maps/place/42%C2%B021'35.0%22N+116%C2%B010'45.0%22E/@41.5339446,116.1155478,98007a,35y,33.89t/data=!3m1!1e3!4m5!3m4!1s0x0:0x72bca4680496990!8m2!3d42.359722!4d116.179167?hl=en

4

BluScr33n t1_is553eo wrote

My answer is a maybe.

There are a series of papers by Wu Siben from the 80s and 90s, like this one, that kind of assume it is a meteorite impact crater. The papers are pretty much all written by Mr. Wu and there seems to be little discussion of the question if it is an impact crater, it seems like he simply assumes it is one and then goes from there.

In contrast, there is this paper from 2017 by Xu et al. that clearly concludes that it is not an impact crater. Instead they found that the region is of volcanic origin. With the big ring structure perhaps being the remnant of an old volcanic caldera.

Personally, the 2017 paper seems much more solid than the old research by Wu. In particular the methods are much better.

3

Wooden_Ad_3096 t1_is4xohj wrote

Hard to tell for me, but I don’t think so.

It’s not circular and there isn’t raised land completely surrounding it.

1

rodeler t1_is1d74d wrote

Why don't I see satellites after sunset or at night during the winter? Is it due to the angulation of Earth relative to the sun? Is it due to air density? Is it a combination of factors?
Background: I live in upstate NY where the skies are generally free of light pollution. I star gaze nearly every night that it is clear. I have noticed that when the air gets cold that I do not see any manmade satellites passing overhead.

3

Moonkai2k t1_is1dwf5 wrote

You see satellites when they have light to reflect. If there's no moon or sun light to reflect in your direction, there's nothing to see. Most of what you see for a reflection is off large flat surfaces like solar panels. If the sun is far enough south you may not get the right angle to see anything at the times you're trying to view. Add to this the fact that most satellites will try to keep their solar panels flat to the sun and you compound the effect.

5

righthandtypist t1_is1ect9 wrote

If near FTL speeds were ever achieved, or even some of the speeds that current satellites are going, how would they effect the human body?

I assume due to the size of the earth and how small we are the speed isn't registered by us due to relative sizes, does this mean that any vessel we create to travel those speeds needs to be proportionally scaled to say moon sized?

3

AtticMuse t1_is1l9d9 wrote

Speeds don't affect the body, only acceleration. So it's not because of the size of the Earth that we don't feel our motion through space, it's because there's fundamentally no difference between being at rest and moving with constant speed relative to something. Think about being on an airplane, apart from any turbulence you feel completely at rest and can move around the cabin normally when cruising, even though you're travelling at several hundred kilometers per hour with respect to the ground.

11

righthandtypist t1_is3de9w wrote

Ah, I wasn't sure if speed mattered in the case of an air plane or not, i guess not looking at the speed of the sr-71 being 2200 mph.

157,000 mph in an airplane just sounds absolutely insane. How would you survive the stop?

2

AtticMuse t1_is3npe6 wrote

The same way you survived the acceleration up to that speed; spread it out over time. Astronauts on the space station are going over 17,000 mph relative to the ground, and getting up to that speed they have to pull a couple of g's in a rocket, which is tough but doable for a few minutes. On their way back to Earth the atmosphere slows them down a little more gradually and they only experience 1-1.7 g's.

And not that we would ever want to stop relative to these things, but just sitting at your desk you're moving incredibly fast through the universe. The Earth is moving ~67,000 mph around the sun. And the sun is moving ~490,000 mph around the center of the galaxy.

1

Nepeta33 t1_is1gckm wrote

Could we make boat sails out of solar panels?

3

remarkablemayonaise t1_is1utli wrote

Yes, but solar panels are designed to be rigid to be structurally sound. There is research to putting thin layer type solar panels where something else is supporting them like on cars. It isn't typically cost effective for most uses, but it's a matter of time.

4

Nepeta33 t1_is1wjbp wrote

there was an article on here a while back about an oil tanker using 6.something % less fuel by using sails in addition to normal propulsion. so i was like, why not use those sails to maybe generate solar energy? if in some far flung future we could make electric motors strong enough to use on tankers, solar sails would be seriously helpful for keeping the batteries going mid trip!

2

Indemnity4 t1_ismxkrz wrote

Interesting thought experiment. It's usually positioned as how much area of solar panels are required to move a train.

At the moment, it seems impossible to build an electric container ship to replace current shipping methods. The goal has moved to building smaller electric boats with batteries that get swapped out at the port. They also make more stops than current ships, which presents an interesting problem with shipping queues at ports...

Panamax style ships have engines about 80 MW in size. Crudely, the batteries required for the duration of the voyage would weigh more than the carrying capacity of the boat. Batteries are really inefficient with poor energy density when compared to almost any liquid/gas fuel.

On-board generation of even 5% of that required energy is 400kW. Plug that into any calculator for roof top solar and you will find the area required is massive.

You also want the solar panel to be angled correctly towards the sun. That's going to decrease the solar efficiency even further. For instance, your sail is probably going to be positioned roughly vertically, instead of the more ideal angled towards the sun or position on a tracking system to orient to the best angle.

1

atomfullerene t1_is6zh7o wrote

The angle wouldn't be great for solar collection. You want to be at right angle to incoming sunlight, it drastically increases the amount of energy you collect.

2

Fewluvatuk t1_is1rdcz wrote

I have a question about Quantum Entanglement.

If I understand things correctly, massless particles travel at the speed of light, and at the speed of light, within the frame of that particle, time is frozen.

If time is frozen within the frame of the particle from the moment it is.... created?.... then is this the explanation for why Quantum Entanglement works the way it does? The two particles are split but no time is passing for them so their orientation can't be set, but when we interact with the particle we interfere with it's frame causing time to begin moving within that frame which is what causes the system to collapse into it's final state? If the two particles had started life not moving at the speed of light would they have already collapsed?

Thanks, really appreciate all of you :)

3

Luenkel t1_is21ef3 wrote

No, this doesn't really make sense. We can and do entangle things which are definitly not moving at the speed of light all the time. So your premise doesn't work.

Also, there aren't any valid frames of reference moving at the speed of light. It doesn't make sense to talk about something "from the perspective of a photon". Just look at the lorentz factor: you're dividing by 0. The only thing you can really talk about is what happens as you approach the speed of light. You could say that time freezes in the limit perhaps.

5

Wooden_Ad_3096 t1_is4xuvu wrote

Anything moving at the speed of light does not have a frame of reference.

1

microcosm315 t1_is1hs6o wrote

I’m still not grasping the concept from the recent nobel prize awarded for proof of the non reality of local space. Am I just misunderstanding the mathematical definitions of words like reality?

2

Wooden_Ad_3096 t1_is4xsqt wrote

Probably.

All it says is that the states of particles aren’t determined until they are observed.

2

microcosm315 t1_is4yapz wrote

Did they demonstrate that in a new way? Seemed like science had already proven that one. It seems similar to the cat in the box (schrodengers?) concept and also to is it a wave or a particle….

1

Wooden_Ad_3096 t1_is4yn05 wrote

Yes, it has been proven some time ago.

Nobel prizes are awarded decades after a discovery.

And Schrodinger’s isn’t true btw.

2

PeanutSalsa t1_is1i9pw wrote

What are some really good books you recommend reading in the Astronomy and Planetary Science fields?

2

Dokino21 t1_is1levy wrote

If our Moon was tidally locked to the Earth, from the beginning, how would the side not always facing the moon be impacted if at all?

Example: Moon in a position that doesn't impact wobble and tilt and is always facing the Eastern Hemisphere.

​

(I'm writing a story and trying to give a scientific reason why life exists on this one continent and thought this could be a reasonable reason why life didn't develop to the same level anywhere else. I'm probably wrong)

2

Brickleberried t1_is1ygag wrote

The Moon is tidally locked to the Earth, but the Earth is not tidally locked to the Moon.

I think if both were tidally locked to each other, such that one side of the Moon always faced one side of Earth, things would be less dynamic. You wouldn't have tides. Earth would be cooler because it wouldn't be flexing and squeezing and stretching from the Moon's shifting gravity (not sure if only a tiny bit or not).

I don't really know of a reason to make it so that it would be better for life on one side or the other of Earth.

The only related idea I can think of it that the Moon's far side has a thicker crust than the near side, which caused more lava flows on the near side. Maybe a similar thing could happen on Earth due to the Mars-sized object that hit the Earth to create the Moon where it knocks off a bunch of crust late in formation? It might not be scientifically possible, but sci-fi just needs to sound somewhat plausible.

3

atomfullerene t1_is6zq58 wrote

>You wouldn't have tides.

You'd still have solar tides, which are about 1/3 of our current tides.

1

atomfullerene t1_is6zv9o wrote

Well, you'd have month-long days. It wouldn't cause life to be on only one side of the planet though.

1

Dokino21 t1_is7rmst wrote

Why would the moon only facing one side of the planet impact the length of days?

1

atomfullerene t1_is7ttc8 wrote

The moon takes a month to go around the earth. If one side of the the earth faces the moon, it must therefore also take a month to rotate.

Granted, a "month" might be much shorter on some other planet if the moon was much closer. For example, pluto's moon charon faces only one side of the planet, but it only takes 6.4 days to orbit.

1

Dokino21 t1_is81el3 wrote

I'm still confused. Why would the moon always facing the eastern hemisphere dictate the duration of the day? The moon would just be up there, staring at us, menacingly day and night. Wouldn't it?

1

Rex_Mundi t1_isaw39q wrote

The presence of the Moon (which has about 1/81 the mass of Earth), is slowing Earth's rotation and extending the day by about 2 milliseconds every 100 years.

2

atomfullerene t1_is82z96 wrote

Think about what it means for the moon to be visible in the sky...that side of the planet has to face the moon. Which means the planet has to take the same time to spin around once as the moon takes to travel around the planet once. Otherwise that side of the planet would get ahead of the moon or get left behind it.

1

Dokino21 t1_is8ln59 wrote

I think I'm missing some vital piece of information in my brain because in my wee brain, I am talking moon is always above my head all the time, it does moon stuff, maybe it rotates like a good boy, but it's always there while the planet does it's rotation around the sun and does it's daily rotation. In my mind, the moon and earth are holding hands while the earth does it's 24 hours a day, 365 a year.

So I am really missing some kind of epiphany in understanding.

1

PeanutSalsa t1_is207y6 wrote

Why does the earth not move closer or farther to/from the sun over time and how solid is the theory explaining why it doesn't?

2

TheMightySwiss t1_is23mlk wrote

It kind of does actually. If you read up about Mylankovitch cycles, you’ll see that there are periods of time where earth spends more time per year further away from the sun, and if you take that and run the simulation let’s say for 1 million years, you’ll see that at some point the climate is plunged into an ice age state, then the cycle reverses and it becomes warmer again (interglacial period), which is where we are now and probably one of the big reasons why we even exist as Homo Sapiens and evolved how we did. However, if you’re talking about a gradual one way movement (like moving closer or further away) over time, then no, it’s not really happening. The orbital radius of Earth should remain the same as long as earth and the sun retain the same mass.

2

Wooden_Ad_3096 t1_is4xyc7 wrote

It does, it’s orbit isn’t a perfect circle.

But if you mean it’s average distance, well it also does, but barely.

Since there really isn’t anything in space, earth isn’t being slowed down by anything, but space isn’t completely empty, so there is a tiny bit of friction.

1

Pitiful_Oven_3425 t1_is2i7kd wrote

Is our understanding of quantum physics limited by how intelligent the human brain is? I. E. Do we need an Einstein to come along every now and then to understand it and be able to convey it in simpler terms to other intelligent people?

2

RippSir t1_is2tkys wrote

I would say quantum physics is mostly math. Some people understand math better than others :)

2

Indemnity4 t1_ismyl9p wrote

Not even close.

Even Einstein got his Nobel prize for discovering the law of the photoelectric effect - not this theory of relativity or quantum mechanics.

Example: almost all quantum physic

Any scientific field is advanced by many eminent thinkers making incremental improvements. "Standing on the shoulders of giants" is the wonderful catch-phrase.

Anytime we look at a list of Nobel prize winners - we tend to find a lot of very clever and hardworking people who have lots of time and experience in their field. They had to work very hard to get lucky.

You also tend to find a larger number of equally skilled people who found the same lucky break just a little bit later, or their work went left on step 47 when the current author went right. They both did really great for the first 46 steps!

The limit is twofold: funding and the public desire to continue that funding.

1

Elektriman t1_is2q9nt wrote

Have we found an exoplanet that rotates so fast that the speed of an object on its surface exceeds the orbit velocity ?

2

Heimskr74 t1_is3c5z6 wrote

Is time quantized? Can there be a smallest unit of time?

2

Indemnity4 t1_isn0831 wrote

Planck time, or the amount of time it takes light to travel one Planck length.

How fast is a Planck time? Planck time is roughly 10^−44 seconds

1

Retiredmech t1_is3m02s wrote

If a alien civilization, say 10 to 50 million light years away developed a JWST and pointed it at our solar system. What and how much information they would they discover about us? I ask this because the JWST is promising to find exoplanets and their composition. I was wondering what it would look like from the opposite side to hopefully understand better on how the telescope works. (this is hypothetical, so imagine the the civilization is 10 to 50 million years in the future and looking at present day)

2

Wooden_Ad_3096 t1_is4y60d wrote

10 to 50 million light years away, they could see the milky way, and that’s about it.

3

Retiredmech t1_is7uvms wrote

I guess my question was a bit vague. How about, at the distance the telescope could detect exoplanets, what they would find out about our solar system?

2

DoctorWho984 t1_isauirw wrote

This article may interest you: It's what the Earth would look like through JWST at 40 light years away.

However, none of the planets in our solar system are particularly amenable to being detected by an instrument like JWST, see here and here. JWST is best at finding exoplanets via transit light curves, and these mostly find "Hot Jupiters" or "Warm Neptunes", planets with larger masses that are much closer to their star than any of the giants in our solar system are to the sun. JWST can also do direct imaging of planets, but that works best for planets that are very far out like Neptune, but also massive, ~10x the mass of Jupiter. So our solar system is not a very good candidate for finding anything at all with just JWST. They'd be most likely to find Jupiter through radial velocity measurements using a optical telescope with better spectral resolution, for example the Keck observatory has likely detected a Jupiter twin.

2

Froggmann5 t1_is1fmuj wrote

Hypothetical question

Imagine you had a 1x1x1 cubic ft area of nothing but space. This is all that exists. Now imagine you teleported in a particle into the middle of this area. Does the total amount of space inside the cube increase, decrease, or stay the same? Does the space inside "move out of the way" to "make room" for the new object?

EDIT: To make it a bit more clear, I'm changing the example from a bowling ball to just a single particle.

1

Brickleberried t1_is1wzmq wrote

Space is just emptiness. It won't expand if you put something in it. Just think of it as an imaginary grid.

3

Froggmann5 t1_is20tr1 wrote

> Space is just emptiness.

I know enough to know that this isn't even remotely true, which is what prompted my question to begin with.

Regardless, this also doesn't answer my question even if it was the case that it was just "emptiness". Since space is a dimension through which all things have relative positions/directions, does the distance across the cubic ft of area I outlined increase, or decrease, if we were to add a particle of matter to it?

If it's 1ft in distance across this space, does adding a particle also add a particles worth of distance to that space?

2

Wooden_Ad_3096 t1_is4y1ez wrote

Nothing changes about the space in that area, since space literally is just nothingness, like the previous guy said.

1

Froggmann5 t1_is5j1pf wrote

> Nothing changes about the space in that area, since space literally is just nothingness

This goes against every paper I can find on Google scholar about the subject. Do you have a source for this?

1

Wooden_Ad_3096 t1_is5j6et wrote

That’s just the definition of space, is it not?

1

Froggmann5 t1_is5k6bl wrote

No. "Nothingness" implies the lack of space. When people talk about the vast distances between objects they talk about "empty space" but not a lack of space itself. Space is separate and distinguishable from nothingness.

1

Indemnity4 t1_ismz8ai wrote

Depends on the walls of the container.

Essentially, you are describing a compressor or something like a bike pump.

In a rigid container you will get a pressure change, but not a volume change.

Example: you have a shipping container and inside is a balloon that is plumbed through the floor into an external air pipe. Suck all the air out of the container. It's full of space (or another way to put it, there is almost zero particles of anything inside the container. For ease of numbers, lets say the pressure in the container is about 10^-4 Torr. Now, pump air into the balloon to expand. You will be compressing the tiny amount of particles inside the container. The walls won't expand, so all you are doing is increasing the pressure in the "empty space". So maybe the pressure goes up to 10^-3 Torr by filling up the volume inside your container with something else.

1

Froggmann5 t1_isofrnw wrote

> Depends on the walls of the container.

The 'walls' of my 'container' are the same 'walls' our universe would have at its 'edge' if it isn't infinite.

The space I'm describing is effectively its own universe, a small 1x1x1 sqft space of space, and that's all there is.

The ultimate end of my question rests on whether or not particles are a type of space. If they are, then they should have a measurable effect on the amount of "space" in an area when present. If they are not then no matter the amount of particles that are inside that space they won't have any impact on how much space is in this universe. (for instance, you could have the same amount of particles that our sun has in its sum total in that same small space and the size of the space would be unaffected completely by the presence of the gargantuan amount of particles).

> You will be compressing the tiny amount of particles inside the container.

This begs the question that I'm asking though, whether or not a particle is a type of space. If it is, then it stands to reason that it would cause a compression effect on the space around it. If not then it would only compress the particles around it and leave the space unaffected.

1

Indemnity4 t1_isv0bnc wrote

> Terry Pratchett — 'In the beginning there was nothing, which exploded.

IMHO your problem is about words and not mathematics. Here are a couple of definitions that hopefully help.

Space is typically defined as absence of "stuff". It has no volume, zero mass, zero momentum, zero electric charge. You can't push it around, or expand it, or do anything to it. Space is dependent on things happening to other stuff.

Particles do have mass, volume, momentum, electric charge, etc. They affect their surroundings.

Interstellar space contains about 100,000 particles per cubic metre. That sounds like a lot, hundreds of thousands!, but it's relatively empty.

Your hypothesis changes depending if you define "space" as interstellar space or as a hard vacuum with all particles removed.

Real world: a random area of interstellar space. If you add one more particle, nothing changes as you've increased the density by a tiny immeasurable amount.

Thought experiment: big container with rigid or flexible walls and absolutely nothing inside. You add one particle. Nothing changes. One particle isn't exerting force on anything, it's not pushing on anything, it's not interacting with your magical thought experiment walls. Nothing changes.

End result of your thought experiment is nothing changes.

1

Froggmann5 t1_isvqxc1 wrote

> Space is typically defined as absence of "stuff". It has no volume, zero mass, zero momentum, zero electric charge. You can't push it around, or expand it, or do anything to it.

You have this completely wrong. The easiest thing I can point you to is that space itself is literally expanding. This has been known, demonstrated, and studied for a long while now.

> Particles do have mass, volume, momentum, electric charge, etc. They affect their surroundings.

This is also at least partially incorrect. Particles like Photons do not have mass for example.

> Your hypothesis changes depending if you define "space" as interstellar space or as a hard vacuum with all particles removed.

I suppose I'll supply this definition of space instead then to make it easier for you to understand the hypothetical:

> the dimensions of height, depth, and width within which all things exist and move.

Moving forward this also shows your misunderstanding of my hypothetical when you try to rebut it with your own example:

> big container with rigid or flexible walls and absolutely nothing inside. You add one particle. Nothing changes. One particle isn't exerting force on anything, it's not pushing on anything, it's not interacting with your magical thought experiment walls. Nothing changes.

This is disanalogous, because your first sentence contradicts. If "Nothing" is inside, how is there an "inside" of the container at all? Saying there's an "inside" implies there's some amount of space within the container for something to be.

In fact this just inspires a better question: If you had a universe of absolutely nothing with no space/time/anything at all, and you add a particle to it, does this also add space to that universe?

> End result of your thought experiment is nothing changes.

I'm afraid your misunderstanding of the very nature of space (and consequently from that, you misunderstood, my hypothetical) led you to this conclusion.

1

Indemnity4 t1_isvznvg wrote

I think a sticking point in any discussion you have is "space"=nothing/vacuum/emptycontainer versus "space"=interstellar medium (where stars and spaceships do their business).

Every person who has responded to you has assumed you are talking about a container full of vacuum. Because that's what those words mean.

One answer to your question about a universe without particles and how to measure it is may be what happened before the Big Bang? The "universe" was a singularity about the size of a peach. However, it was full of stuff and not empty.

The other answer is what is outside our universe? e.g. you have an area of "space" with nothing in it, then you add a particle, what happens?

The answer is... nobody knows. The observable universe has always had stuff in it, so the size/distance/volume is measure by taking two of those points. Physics no longer works when you are talking about a universe without particles. There is no distance unless you are measuring how far apart two things are. There is no pressure without having a container.

Your scenario of a "universe" with nothing it but somehow it has reference points for scale 1m x 1m x 1m, that can't happen. There is no way to get a reference point.

Maybe the closest you will get is within string theory - it lets you have a "universe" without particles. At some point the universe was a mass of 1 dimensional strings vibrating (so we don't have 3 dimension like 1m x 1m x 1m anymore). One of those flipping in a weird way that lead to the formation of the first particle. That caused a chain reaction which created more and more particles that lead to the universe.

1

Cartmansimon t1_is1vq84 wrote

Gravity is measured at 9.8m/s. Would we notice a difference if that somehow changed to 9.75m/s, or would the change have to be more drastic to notice a difference?

1

Yaver_Mbizi t1_is2a91r wrote

The unit for free-fall acceleration (as well as all other accelerations) is m/(s)^2, by the way, not m/s. m/s would be a velocity.

3

Brickleberried t1_is1x5qy wrote

It would be very noticeable to a great many things, but probably not if you're just walking around. It would be around 1 pound of difference you would feel in your weight.

2

OlympusMons94 t1_is2lu3h wrote

If you just went to a place where the free fall acceleration was 9.75 m/s^(2), you wouldn't notice any difference unless you measured it. The average American would weigh about 1 lb or 0.5 kg-weight less than they usually do. Just due to eating and other bodily processes, your weight varies by more than that over the course of a day.

There is nothing special about the *exact* value of 9.8 m/s^(2) (or the standard gravitational acceleration of 9.80665 m/s^(2)) other than that it is a standard chosen for convenient reasons. It is just the approximate average free fall acceleration on Earth's surface. The actual value varies over the surface of Earth because it is not a perfect sphere. Not only are there an equatorial bulge and flattened poles, but there is topography like mountains. The acceleration due to gravity decreases with the square of distance from the center of mass, so it is higher at the poles and lower at the equator, and lowest (on the surface) at mountaintops near the equator. Centrifugal acceleration from Earth's rotation also acts to reduce the effective or net acceleration. Centrifugal acceleration is zero at the poles and highest at the equator. Altogether, the average acceleration the equator is about 1% lower than at the poles. The lowest acceleration on Earth's surface is about 9.76 m/s^(2), at the summit of Mt. Chimborazzo in Ecuador.

Now, if something happened to the physical constants of the universe or even just the properties of Earth so that the average acceleration became 9.75 m/s2, that could be significant--quite possibly an "everybody dies" scenario.

1

mudplugg t1_is3mt6r wrote

If the big bang comes from an ¿infinitely? dense point, and black holes crush things to an ¿infinitely? dense point - could every black hole be the big bang of another universe? Or are there fundementals of science that makes this impossible?

1

Wooden_Ad_3096 t1_is4y9es wrote

Common misconception.

So first, the singularity in a black hole and the one at the big bang are not the same.

The one in the black hole is an infinitely dense point, while the one at the big bang is just infinitely dense.

Second, those singularities don’t actually exist, they are just a product of our incomplete theories.

1

timhamlin t1_is3xvud wrote

Since space is expanding ( I assume that means all space). Is there a known measurement of that amount? And isn’t it true that we r all larger by that proportion? As measured on a cosmicly meta scale (outside of space).

1

Wooden_Ad_3096 t1_is4yi6h wrote

The universe is expanding at a rate of 73.3 kilometers per second per mega parsec.

And no, everything isn’t getting bigger because of that. Gravity counteracts the expansion, so it has no affect at our scales.

The expansion really only affects intergalactic scales.

1

timhamlin t1_is5dugg wrote

Ok. The expansion on human scale is tiny? But not zero? So on a scale that is external to space (measuring from outside the perspective of being IN space) how much bigger r we compared to the past. Or am I totally off on this?

1

Wooden_Ad_3096 t1_is5e3is wrote

We are the same size because gravity and electromagnetism counteracts the expansion.

Basically the expansion “pushes” two things apart, but if they are close enough, their gravity will just pull them together faster.

3

ExamOk4257 t1_is4og7j wrote

If space is foldable, what would happen if 2 black holes with same mass, speed and size, fold on top of each other, do they fizzle out, combine or just mantain the status quo?

Another one, can space be considered a 2 dimension and the universe is made out of an infinite 2 dimension planes layered on top of each other ?

1

Wooden_Ad_3096 t1_is4yk72 wrote

  1. Not sure what you mean by “foldable”.

  2. I guess? I don’t know why you would though.

1

[deleted] t1_is545jm wrote

[deleted]

1

Wooden_Ad_3096 t1_is548r0 wrote

Why did you think repeating the same exact comment would help me understand what you’re trying to say?

1

ExamOk4257 t1_is553hs wrote

The thing i was saying it is said that space-time can be warped or bent to such a degree that it can become a infinite closed loop, as my question i wondered that would happen to 2 black holes of the same size, speed , mass, that exist on the same 2D space-time "sheet" would overlap on top of each other.

1

Wooden_Ad_3096 t1_is558zt wrote

They would… merge, I guess.

What you’re saying just sounds like a convoluted way of describing a black hole collision.

1

ExamOk4257 t1_is56sqy wrote

I was asking about the oposite of an Einstein-Rosen Bridge, since both black holes have the same stats, with infinite gravity would they feed of each other in an infinite loop or fizzle out. But i guess this is just hypothetical question.

1

PeanutSalsa t1_is625c2 wrote

When it's said the universe is expanding is this only referring to the galaxies moving away from each other or does it include space around the galaxies too?

1

cb3f554 t1_is65hpy wrote

Currently expansion exists only on the largest scales (between galaxies). The space around the galaxy is also expanding, but the gravity of the galaxy keeps itself together so no expansion inside (yet)

1