Ask a physicist anything. (6)

[hisgrace26]

You mean, are you asking if your god could have made a young universe look as if it were old? Well, in principle, sure, why not? Your god is claimed to be all-powerful, after all. In principle, an all-powerful god could do anything at all. But the problem with that is that it presupposes that your god is deceptive. And if you believe there is an all-powerful deceiver god out there, then you can't trust anything at all.

No.... God is not deceptive. It is our human flaws and limited scientific tools to even measure these distances. Are you crazy? God could have just made it recently and flung the heavens out when in fact it's only few thousand years. Stars are very far away indeed. But to measure these distances based on the redshift and the brightness of these stars - that's just impossible.

 

[hisgrace26]

Well, there are two ways in which gravity can affect the redshift. One is if the light is coming from very, very close to an extremely dense object, such as a black hole. The other is due to intervening space-time curvature.

As far as the light coming from very close to an extremely dense object is concerned, well, this generally isn't a problem, because the vast majority of things we observe are not matter falling into black holes. And of those that are matter falling into black holes, typically we see not only matter that is just about to enter the black hole but also matter that is further away, so we can easily correct for the effect.

As far as intervening space-time curvature is concerned, well, that's the same as relative velocity. That may sound a little bit strange, but in General Relativity, whether a far-away object is moving away from us or not depends entirely upon what coordinate you use. I can describe a far-away object as moving away and the intervening space-time curvature as being flat, or I can describe a far-away object as being stationary and the intervening space-time curvature as being highly curved. In either case, I get the same redshift. It just depends on what coordinates I use. Whether the expansion is due to space-time curvature or velocity are just two different ways to talk about the exact same physical effect.

And something can absorb the light and only be like 20 feet away. You can make the wrong assumption thinking that because it's far away, therefore it must take that same amount of time for light to get here. Error in logic right there.

 

[Tim the Plumber]

No.... God is not deceptive. It is our human flaws and limited scientific tools to even measure these distances. Are you crazy? God could have just made it recently and flung the heavens out when in fact it's only few thousand years. Stars are very far away indeed. But to measure these distances based on the redshift and the brightness of these stars - that's just impossible.

No. The stars very far away are very far away.

The light has travelled billions of years to get here. This is very proovable.

The degree to which the figures the astrophisicists come out with are precisely acurate are often a bit vague. However when they say that such and such a galaxy is 10 billion light years away they are acurate to the degree of + or - 1 billion years. It's a very very very very long way away whichever number you use.

 

[Wiccan_Child]

Consideroing the spin down rate of the earth. How long was the first day?
How much sun light and how how long was the darkness?

4.5 billion years ago, when the Sun and Earth first formed, the Earth took about 6 hours to rotate. This equates to 3 hours of sunlight, 3 hours of daylight, not factoring in seasonal variation.

 

[Cabal]

No.... God is not deceptive. It is our human flaws and limited scientific tools to even measure these distances. Are you crazy? God could have just made it recently and flung the heavens out when in fact it's only few thousand years. Stars are very far away indeed. But to measure these distances based on the redshift and the brightness of these stars - that's just impossible.

Got an actual refutation to the very detailed explanations you were given other than your personal belief that it's "impossible"?

 

[Jazer]

4.5 billion years ago, when the Sun and Earth first formed, the Earth took about 6 hours to rotate. This equates to 3 hours of sunlight, 3 hours of daylight, not factoring in seasonal variation.

Ok, if the moon is moving away from the earth, how long ago did the moon bounce off of the earth.

 

[chris4243]

Got an actual refutation to the very detailed explanations you were given other than your personal belief that it's "impossible"?

BTW, what do you think of my avatar?

 

[Cabal]

BTW, what do you think of my avatar?

Why do you ask?

 

[Davian]

Ok, if the moon is moving away from the earth, how long ago did the moon bounce off of the earth.

Do you understand why the moon is slowly moving away from the earth? And why the earth rotation is slowing?

 

[Chalnoth]

Ok thank you...but is it right to say then that the relationship between the object and it's shadow is one of projection?

Right, exactly.

 

[Wiccan_Child]

Ok, if the moon is moving away from the earth, how long ago did the moon bounce off of the earth.

The Moon formed around the same time as the Earth did, about 4.5 billion years ago. Its original distance was about 20,000 km from the Earth, but as it recedes from the Earth, this distance has increased to its current value of about 384,000 km. However, this recession velocity is itself variable, and although it's a paltry 3.8cm/yr now, it was quite faster in the past. Nonetheless, the closet the Moon has been was 20,000 km - closer than today, but by no means bouncing off the Earth.

 

[Wiccan_Child]

BTW, what do you think of my avatar?

I think it's quite darling.

 

[Wiccan_Child]

No.... God is not deceptive. It is our human flaws and limited scientific tools to even measure these distances. Are you crazy? God could have just made it recently and flung the heavens out when in fact it's only few thousand years. Stars are very far away indeed. But to measure these distances based on the redshift and the brightness of these stars - that's just impossible.

Err... no, it's not. Chalnoth and myself just went through how it works. Why do you think it's impossible? What fundamental logical flaw have we made that renders it impossible?

 

[Chalnoth]

No.... God is not deceptive. It is our human flaws and limited scientific tools to even measure these distances. Are you crazy? God could have just made it recently and flung the heavens out when in fact it's only few thousand years.

Let's say a strange comes up to you. He says that aliens created the Earth, and gave it a green sky. You tell him, "What are you talking about? Look up! The sky is blue!" He says to you, "But that's just our flawed and limited understanding. It's really green. The aliens just put a filter on the sky to make it look blue to us."

What would you say back to him?

Stars are very far away indeed. But to measure these distances based on the redshift and the brightness of these stars - that's just impossible.

It's not trivial, but it is nowhere near impossible. To people that have actually studied this stuff, telling them that you can't measure distances to stars is like telling somebody they can't look up and see the blue color of the sky. It's nuts. The way it is done in reality is through a large variety of methods which are checked against one another for consistency. Each method has different assumptions, and if you change the laws of physics in one way, e.g. by changing the speed of light at early times, then different distance measurement methods will give you very different results.

The simplest and most direct method of measuring distances is parallax. To measure the distance to a star via parallax, we first look at the star one night, then we wait six months and look at the star again, measuring how much that star has shifted.

The idea here is that in six months, the Earth travels halfway around the Sun: it moves by a distance equal to the diameter of Earth's orbit (nearly 200 million miles). And if the star shifts in its position by a measurable amount, then that makes for a triangle: the amount it shifts gives us the angles of the base of the triangle, and with the angles and the length of the base, we can calculate the distance to the star. This method is useful for measuring the distances to stars up to a few thousand light years, allowing us to calibrate our other distance measurements.

 

[Chalnoth]

And something can absorb the light and only be like 20 feet away. You can make the wrong assumption thinking that because it's far away, therefore it must take that same amount of time for light to get here. Error in logic right there.

It's not an assumption. Not in the least. Because light is an electromagnetic wave, its behavior is intertwined with the behavior of the electromagnetic force. You cannot change the speed of light without changing the behavior of the electromagnetic force, and thus the behavior of matter. So when we see matter very far away that is acting in a manner consistent with the laws of physics we measure here on Earth, we gain confidence that the speed of light cannot have been very different when the matter emitted that light.

 

[Insane_Duck]

Here is a silly question I have:

Helium balloons rise because they are lighter than the surrounding air. Since a helium balloon's contents is sealed off from the surrounding air, how does it know to rise? (if it can't interact with the surrounding air)

Could these sort of disturbances be used to transmit information instantaneously?

 

[Tinker Grey]

Here is a silly question I have:

Helium balloons rise because they are lighter than the surrounding air. Since a helium balloon's contents is sealed off from the surrounding air, how does it know to rise? (if it can't interact with the surrounding air)

Could these sort of disturbances be used to transmit information instantaneously?

I'll take a stab at it. (Hope it doesn't pop!)

It is because the sum of the mass of the ballon fabric and the helium is lighter than the surrounding air (less dense). That is, the whole balloon including the mylar/elastic/whatever is less dense than the air.

Imagine a balloon of a traditional size made of lead. It doesn't rise because the whole object including the lead is too dense.

ETA: I don't know what you mean by distrubances. Sorry.

 

[pgp_protector]

I'll take a stab at it. (Hope it doesn't pop!)

It is because the sum of the mass of the ballon fabric and the helium is lighter than the surrounding air (less dense). That is, the whole balloon including the mylar/elastic/whatever is less dense than the air.

Imagine a balloon of a traditional size made of lead. It doesn't rise because the whole object including the lead is too dense.

ETA: I don't know what you mean by distrubances. Sorry.

Ya just need a larger balloon for the lead balloon to work

 

[Jazer]

closer than today, but by no means bouncing off the Earth.

So how does the moon tilt the earth?

 

[Insane_Duck]

Ya just need a larger balloon for the lead balloon to work

Mythbusters actually got a lead balloon to fly.