Milky Way Andromeda fusion

[leroy]

Milky Way Andromeda fusion

I´ve been having this question for years, I tried to find the answer on google and I failed, I tried to find an answer in yahoo answers and I failed, so I will simple give it a try in this forum.

The question is:
If the galaxy is moving towards Andromeda by gravitational attraction, why can´t feel this movement? Why can´t we perceive that the galaxy is moving?
I am making 2 assumptions

1 Humans can´t feel constant speeds, but we can feel accelerated movements.

2 we are moving towards Andromeda at an accelerated speed.
Given these assumptions that as far as I know are obviously true, shouldn´t we feel the accelerated movement in our galaxy?

 

[Inferno]

Wikipedia

I don't know if your assumptions are correct, but let's assume they are. The collision will take place in a few billion years (roughly 4 billion), so that's a long way off. There are a lot of other forces out there, so my guess would be:
1) It's too little attraction.
2) The tug and movement inside our solar system is much greater than that of the Andromeda Galaxy.

That being said, I'm not sure your premise is correct, though others are better versed in this.

 

[Deleted member 619]

I am making 2 assumptions

1 Humans can´t feel constant speeds, but we can feel accelerated movements.

2 we are moving towards Andromeda at an accelerated speed.
Given these assumptions that as far as I know are obviously true, shouldn´t we feel the accelerated movement in our galaxy?

3. That the reason that Andromeda and Via Galactica are moving toward each other is because of gravity.

All of these assumptions are incorrect.

Dealing with the question itself, there's a very good approach to answering it, namely to ask why you don't feel the gravitational attraction of Jupiter? The answer is that the attraction is there, but it's far outweighed by the gravitational attraction of the Earth. Indeed, I often note when dealing with astrology types who insist that the mechanism behind the influence of the planets on our lives is via gravity that their charts should also take into account the position of the midwife, whose gravitational influence on a delivering mother far outweighs that of any of the planets.

It also might be worth finding out precisely what 'acceleration' means in physics, because that's a source of much misconception, as it doesn't reflect the vernacular meaning.

ETA: Can you feel the acceleration of Earth throughout its orbit? Work out the answer to that question and you'll have it all worked out.

 

[leroy]

I am making 2

ETA: Can you feel the acceleration of Earth throughout its orbit? Work out the answer to that question and you'll have it all worked out.

No, because in that case the acceleration is Zero

.
However since we are moving towards Andromeda at a speed of 300 k/h and WITH POSITIVE acceleration we should feel the movement.

 

[Dragan Glas]

Greetings,

No, because in that case the acceleration is Zero
.
However since we are moving towards Andromeda at a speed of 300 k/h and WITH POSITIVE acceleration we should feel the movement.

Due to gravity we don't experience any movement - whether the Earth's rotation/orbit, the solar system's or galaxy's movement through space.

Even the acceleration isn't detectable.

Kindest regards,

James

 

[Master_Ghost_Knight]

1 Humans can´t feel constant speeds, but we can feel accelerated movements.

Actually, no you can't.
What you can feel is the difference in acceleration between 2 different parts of your body, but that is because that difference in acceleration causes the geometry of your body to change, and become either farther apart or closer together than they were before, and your internal sensors would detect this stretching. If every part of your body is accelerated by the same amount, there is literally no experiment that would allow you to tell if you were accelerating or not. Just to point something quickly, as we move around the sun the earth and by extension us are being constantly accelerated, do you feel the thug of the sun?
We can still devise very sensitive equipment that can detect that.

But if we are talking about wider bodies and larger distances in proportion to your experiment, meaning that the distance between your experiment and that celestial body is much much larger than the farthest distance between 2 sensible points of your experiment, and the apparent width of the celestial body in proportion to its distance is much much larger than that of the experiment. Which certainly Andromeda does qualify in relation to any experimental apparatus that we ever devised, the gravity field would have been so smooth that the most sensitive of instruments wouldn't able to register. No to mention the fact that any change of registering anything is completely drowned by the fact that you have a gigantic source or gravitational noise called the sun, planets... well the solar system.
In such a condition, it is almost impossible to devise an experiment that could tell either or not it was under the influence of an acceleration while inside a black box.

Of course if you were not in a black box you could know because you would see things coming closer and closer to you at ever faster rates.

However since we are moving towards Andromeda at a speed of 300 k/h and WITH POSITIVE acceleration we should feel the movement.

As I explained, no you shouldn't feel it at all. But that point I have already made, I want to point something else.
There is indeed an acceleration, do you have any idea how much that is? Just a ball park figure, how much? Because that is extremely important. I will tell you later if you can't do it yourself.

 

[leroy]

As I explained, no you shouldn't feel it at all. But that point I have already made, I want to point something else.
There is indeed an acceleration, do you have any idea how much that is? Just a ball park figure, how much? Because that is extremely important. I will tell you later if you can't do it yourself.

So are you saying that the reason why we can´t feel it is because the acceleration is very small?

So if our galaxy suddenly stops moving, would we experience something? I mean if you drive a car and you suddenly stop, you obviously feel something, (you move forward)

While I was typing the answer, I think I kind of get it. The reason why we feel the acceleration (change in speed) in cars is because they change at a different rate than us, in the case of our galaxy, this change in speed occurs in all the galaxy at the same rate. ¿is that correct?

thanks

 

[Master_Ghost_Knight]

So are you saying that the reason why we can´t feel it is because the acceleration is very small?

Well the reason why you can't fell it is because the gradient (i.e. how the force changes from one point in space to the next) is imperceptible at our scales even if the acceleration was enormous. But that was not what I was trying to say with that last part, what I was trying to say is that the acceleration is not even great.

What I was saying with that last bit was the intensity of the effect matters, and in this case the acceleration is so small, that even if I were to ignore certain bits of physics like that previous part about the gradient, there wouldn't be enough acceleration for you to notice.

I mean if you drive a car and you suddenly stop, you obviously feel something, (you move forward)

But the reason why you feel it when you drive a car is because the acceleration is transmitted through your skin. When you break, your seat belt pushes on the skin on your chest that goes on to push on your rib-cage, your butt cheeks gets pulled by the fridges of your seat, while your head and your guts keep moving forward in accordance to newtons first law, just to find out that the rib-cage now stands in the way and that your neck is lagging behind. This will cause parts of your body to squish and pull, and it is the squishing and pulling that you feel.
But gravity is different, gravity permeates through your entire body, and it will pull through your entire body almost the same way, so it will move all your body parts the same amount, thus there is no pulling or squishing, and thus you can't feel it.

The reason why we feel the acceleration (change in speed) in cars is because they change at a different rate than us,

Yes, you get it.

in the case of our galaxy, this change in speed occurs in all the galaxy at the same rate. ¿is that correct?

Well almost, it is not the same through out the entire galaxy. It is just that at small distance scales, let's say our solar system, the change in speed (i.e. acceleration) feels as if it was the same everywhere.
But yes, you get the idea.

 

[leroy]

thanks