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Physics, Astronomy & Cosmology / Re: Are Black Holes Real? Is Time Travel Possible?

« on: 16/01/2025 16:40:03 »

Black holes do exist, as we have actually been able to image one. As for the singularity, that is an open question.  While some might describe it as a point of infinite density, it would be more accurately described as the point where our math breaks down.  It is very possible that when things get that small, other effects come into play which would prevent this from occurring.  As for being a passage to other points and times, while this isn't entirely ruled out by the math, the likelihood his small. Any representation of time travel you come across in a novel, TV show, or movie isn't going to be scientifically based, as the rules for such time travel will molded to fit the story being told. 

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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 15/10/2024 17:58:34 »

You have put your finger on  the misunderstanding that pervades much of this discussion!

Accelerating a clock alters its tick rate, so when the traveller returns, the discrepancy between the elapsed times of the erstwhile twins depends on how long he has been away and what accelerations he has experienced in the trip.

No, it does not effect it's tick rate, it alters how it would consider other clock's tick rates compared to it own.  Clocks in the direction of the acceleration would be ticking faster compared to his own, and those in the opposite direction slower ( this is in addition to any Doppler shift due to relative velocity).   The difference in tick rate increases with distance in these directions.

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New Theories / Re: Do light particles have the mass density of black holes?

« on: 10/08/2024 15:35:36 »

Photons can never be at rest, they don't have any "rest mass", and c is not a valid inertial frame to which you can apply the Lorentz contraction.  That's three strikes right there.

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Physics, Astronomy & Cosmology / Re: Where are the round rocks on Mars ?

« on: 20/05/2024 16:47:18 »

They probably never existed, or haven't yet evolved.

Rocks tend to fracture with straight edges. You need the erosive action of grit-laden water or wind to polish them into smooth shapes, and Mars seems somewhat deficient in both.

The alternative source of mineral rotundity can be a volcanic eruption of liquid that freezes slowly as it descends through a viscous atmosphere. but again Mars isn't the best place to manufacture lead shot by that traditional process.   

Umpteen years ago the New Scientist published a question about the distribution of flat stones on a seashore. My 6-year-old son pointed out that all the good ones will have been thrown into the sea by small boys, so you won't find many above the high water mark. Extrapolating from that wisdom, and from the Apollo program of exporting human stupidity to other planets, I think you might find round rocks inside the so-called craters that form the Mars crazy golf course. 

Your son is amazing !

I would have thought over the zillions of years with all the epic sand storms  that weathering would have happened by now. However, I acquiesce to your your sons prodigious wisdom ! 😉

The "dust" storms on Mars are not all that epic.  The highest wind speeds have only reached ~60mph, and this isn't typical. And given that the atmosphere is only 1/100 as dense as the Earth's they don't have much punch.  They may be "epic" in size, covering vast areas of Mars, but not in strength.

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Question of the Week / Re: QotW - 24.05.17 - Are the laws of physics are the same across the universe?

« on: 10/05/2024 12:40:26 »

We receive electromagnetic radiation of all kinds from different parts of the universe; radio waves, visible light, infrared, etc.  When we examine that light, we see the same lines in the spectrum as those produced by elements here on Earth, and no evidence that the basic principles governing behavior there differs from those locally. 
That is not to say that we have discovered all these basic principles, as there are  number of unanswered questions. So it would be possible for said civilization to have pierced the veil more deeply and has a better understanding of those principles than we do.  This would not constitute a change in the rules, but just a better understanding of what they are.

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General Science / Re: Why is each solar day a couple of minutes faster or slower than the previous?

« on: 22/04/2024 16:46:14 »

How long before the slowing of the earth's rotation will force us to choose between retaining 86400 seconds in a day and retaining the current definition of the second?

At a rate of 1.7 ms per century,  58,000-59,000 years for the Earth's rotation to increase by 1 sec. The definition of a sec is unlikely to change, as it it tied to so many things in physics.  What will happen is that, as time goes on, leap seconds will be added more and more frequently.  But by the time it becomes necessary to add one a day, I'm sure our clocks will be able to do it pretty much automatically as needed.

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General Science / Re: Why is each solar day a couple of minutes faster or slower than the previous?

« on: 20/04/2024 16:59:53 »

Just to clarify on Halc's post at bit.  As stated, the physical rotation of the Earth remains pretty constant.  The Solar day, however is a result of this rotation and the Earth's orbit around the Sun. In a Sidereal day, the Earth has traveled a bit under 1 degree of it orbit. So, in order to Bring the Sun back to it noon position, the Earth has to rotate a bit more. Thus the Solar day, is roughly 4 min longer than the Sidereal day. 
The Earth's orbit is not perfectly circular, and due to orbital mechanics, varies its orbital speed over its course.  This alters slightly how much of its orbit it travels in  a sidereal day, and thus the length of the Solar day.   The Earth's axial tilt also plays a role in the apparent solar day length during the year, since the Earth's axial rotation is not aligned with its orbital one.

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Physics, Astronomy & Cosmology / Re: Did the Sun change from orange to white 15 years ago?

« on: 11/04/2024 15:21:03 »

I can tell you this: The Sun has not changed color in the 65 yrs that I've been around.

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Physics, Astronomy & Cosmology / Re: Does time dilation and length contraction apply to light?

« on: 07/04/2024 15:59:27 »

Krytptid's thoughts here mirror mine very closely and it seems I have a major gap in my understanding of SR(not surprising really). If one could travel at the speed of light surely one's rapidity would be infinite and hence time and space would have no existence- why does this not apply to light?. I have heard several physicists state that "light does not experience time or space" or something similar expressed more accurately: I cannot remember any names other than the mathematician Roger Penrose(who can be controversial at times). This question of mine is a bit muddled but I could not find a better wording. 

"If one could travel at the speed of light ..."  That's the issue.  Anything that travels at c would be in the same boat as light.
Consider the equation for relativist KE:
KE = mc^c (1/sqrt(1-v^2/c^2)-1)   if v=c, then it reduces to :
KE mc^2(1/0-1) 
Note the 1/0.  1/0 is undefined, thus the KE of a mass traveling at c would be undefined. Just like the singularity, the math doesn't give an answer for this scenario.
So when you post "If one could travel at the speed of light ...", you are essentially saying, "If Relativity doesn't hold..."

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Chemistry / Re: What ingredients are in the withdrawn Takata airbags?

« on: 14/03/2024 14:48:59 »

The problem was that the airbags used phase stabilized Ammonia Nitrate, and that they did not include a desiccant.  Over time, humidity and high temps degraded the Ammonia Nitrate.  This led to it burning too quickly.  This, in turn, led to pressures inside the inflators beyond that which they could withstand, causing them to explode, spewing shrapnel.

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Physics, Astronomy & Cosmology / Re: If Red Light cures everything, why aren't hospital lightbulbs red?

« on: 27/02/2024 15:12:33 »

Red light does indeed penetrate the epidermis to a greater extent than blue, but all the "red light therapy" installations I have seen (I get involved with a lot of "fringe" stuff!) also produce a fair bit of radiant heat, free coffee, and pleasant music. Plus handsome, enthusiastic, young therapists.

 The dark-adapted human eye is  more sensitive to red light, which is why it is used in cockpits and ships' bridges at night.

No. It is because red light doesn't trigger the transition from night vision to day vision. Night vision uses the rods of our eyes, and they start activating due to the production of rhodopsin, which takes a good bit of time become fully effective.  It reacts with and decays rapidly when exposed to high enough levels of light.  Thus when your eyes have become dark adaptive, and you look at a bright light, this neutralizes the rhodopsin, shuts down the rods, and you lose your dark adaptation.
Rhodopsin is not sensitive to red light*, so it doesn't break down, thus preserving your dark adaptation.  The red light in ship bridges and cockpits at night is to preserve the occupants' night vision, allowing them to see outside better. 

* The photosensitive chemicals used for black and white photography are the same way, which is why you can use a red "safe-light" in a darkroom while developing.

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New Theories / Re: Mechanics of comet motion

« on: 25/02/2024 15:54:41 »

This guy has been posting this stuff on other sites, and his posts and responses here are word for word what he's posted elsewhere.  So, all you're likely to get as a response is a copy and paste.

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Physics, Astronomy & Cosmology / Re: Would a gigantic stick out of neutronium bend around the Sun?

« on: 22/02/2024 16:47:16 »

This part I don't get (science is not my strong suit). I thought that space is bent around the star, so how can this stick defy space that is bent, even if equipped with EM field?

"Space-time" is said to be "curved".   In Relativity, space and time are not the separate and distinct things they were considered in Newtonian physics.  So, we have three spatial dimensions, Up-down, left-right, front-back. and a time dimension, past-future.  and they are all "connected" in a way.   

And saying that space-time is curved means that it doesn't adhere to the Euclidean rules of geometry.
Now, that being said, it is also important to remember that space-time is not some rigid structure that everything is fixed within. If that were the case, then movement would be impossible. Everything would be frozen in its point in space-time.
Nothing is "forced" to follow the local space-time curvature.  In can exert an influence, but it is not in insurmountable.  Local influences and forces can take precedent.
For example: The universe is expanding, and this is explained by space itself expanding. But this does not mean everything in the universe is expanding.  You are not expanding. Earth is not expanding, the solar system is not expanding, our galaxy is not expanding. This is because there are other influences (molecular forces, gravity) that hold these things in shape despite space itself expanding.

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General Science / Re: Can there be water on the moon?

« on: 13/02/2024 16:15:29 »

I see talk of an expedition to find water at one of the lunar poles. I would have thought any frozen water would have sublimed in the high vacuum that exists on the moon.

As long as the water is in a crater or other permanently shaded spot, it shouldn't be any more susceptible than ice in a comet far from the Sun. If mere exposure to a vacuum were enough, by now there would not be any icy bodies in the Solar system. 

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Physics, Astronomy & Cosmology / Re: If Andromeda is red shifted how can we collide with it?

« on: 28/01/2024 16:17:25 »

Andromeda is moving away from us as it is red shifted.  And yet we are going to collide with it. So how can we collide with an object that is red shifted?

It should be blue shifted if it is heading our way regardless of the universe expansion.

If the local gravity is overcoming the expansion and that is the explanation for our collision then how can it be red shifted when we observe it? 

(local dynamics, such as the gravitational interaction between the Milky Way and Andromeda, cannot explain why Andromeda's light appears redshifted if it is indeed moving towards us).

Andromeda is blue shifted.   It is part of our local group of galaxies which are gravitationally bound to each other.  The Universe is composed as a hierarchy of structures.  Star systems group together to form galaxies, individual galaxies form groups, groups form clusters...  It isn't until you get beyond the cluster stage that you begin to see the effects of the expansion.  So when it's said that the galaxies are receding from each other, it really means that structures that are formed from galaxies and are beyond a certain size are receding from each other.

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General Science / Re: Yellow and Purple.

« on: 21/12/2023 16:52:07 »

alancalverd is likely on to something; You find Purple depressing because you associate it with something depressing in your past. 

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Physics, Astronomy & Cosmology / Re: Has E=mc2 been proved practically?

« on: 09/12/2023 17:18:52 »

AC electricity moves at the speed of E/M light and is massless just like photons. So 50/60 cycle per second domestic electricity could  just be very low frequency E/M light. 
Further problem is particles cannot accelerate to light speed without a huge amount of energy being pumped in.
So we need to rethink how we visualise electricity and the parameters surrounding photons inside a conductor.

No, it doesn't.  The drift velocity of the electrons is really quite low, and even the effective speed ( like the time it takes between flipping a switch and the light coming on) can be as slow as 2/3c, depending on the conductor. 
Quite frankly, it sound like your objections to the present model for the conduction of electricity is based on a lack of knowledge of what the present model actually is.

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Physics, Astronomy & Cosmology / Re: Why do the Earth's satellites orbit longer than the Moon's?

« on: 08/12/2023 17:01:02 »

I'm going to take a stab at what he might be getting at.
He may be talking about the stability of orbits around these two bodies.
If that is the case, then yes, low lunar orbits do tend to be less stable than low Earth orbits.
This is caused by mascons (mass concentrations)  randomly scattered under the Moon's surface. These are regions where the density is significantly higher than average, and this, in turn, tends to make the gravitational field nearer to the Moon a bit uneven which can disrupt the orbits of objects there.

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Physics, Astronomy & Cosmology / Re: Has E=mc2 been proved practically?

« on: 08/12/2023 16:46:23 »

Electro-magnetic energy is fundamental energy has the formula = V*A *Cosineϴ*Time.
But if Cosineϴ is zero then even with volts and amps present we have no power energy only quantum power energy

That formula refers to  specific situation when you are dealing with an alternating current and a circuit with either capacitive or inductive reactance.  In such an instance, the voltage and current can be out of phase with each other, the difference in phase angle is what you are taking the cosine of to get effective  power usage of the circuit.  If the circuit were purely resistive, than there is no phase difference and you can just multiply volts times amp to get watts and then that by time to get energy usage.
 It has nothing to do with the "fundamental energy" of electromagnetic energy.

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Physics, Astronomy & Cosmology / Re: Has E=mc2 been proved practically?

« on: 06/12/2023 16:32:22 »

Yes,   E = hf. but what length or area dimension are you measuring in.  Energy must occupy a volume it cannot be described physically without volume in cubic Metres x,y,z especially as it has no mass in Kg. Time in Seconds is relative.
 MKS has a problem describing electricity and electro-magnetic light.

Energy is a property.  It makes no more sense to say that energy must occupy a volume than it does to say weight must have a length.