A Visual Model of Relativity

Updated 22 Sep 26

I've updated and re-instated this document on the RetroMat website. It goes from Special Relativity to a specific case from General Relativity using a simple visual model, some reasonable assumptions and relatively (!) simple maths, with not a tensor in sight!

'Upgrading' a Linux PC

A departure from my usual retro theme...

Until last year, I'd been happily using a laptop bought in 2008! It had been shelved for many years and when I retired was brought back into service, but running Lubuntu, a lightweight distribution of Ubuntu Linux for the desktop. Incredibly, it served me well for about four years.

Last year, my wife replaced her laptop, so that she could run Windows 11. It was a mere(!) 7 years old and had (and still has IMO) a decent spec., but Microsoft had decided they weren't going to support it, so I took it over. Lubuntu were abandoning the lightweight aspect, so I decided that I may as well use another distribution and settled on Linux Mint instead, another Ubuntu variant.

It was OK, but the mouse pointer was often replaced by a spinning icon, indicating the system was a bit too busy to devote itself to my needs. There was the odd glitch and Ubuntu itself is now becoming resource-hungry, with a (crazy, IMO) minimum memory requirement of 6 GB, so I decided to replace it and chose Fedora Workstation.

I started and seemingly made reasonable progress at first. True, it was a faff trying to boot from a USB key with the new OS, but that's BIOS (or UEFI) for you. (A further complication for me is that not all USB ports on my laptop can be used for booting).  The OS seemed to get installed, but I was left with a simple screen, no menu and just (so I thought) the ability to alter some settings by right-clicking the mouse. I rebooted the machine, thinking that would fix it, but was left with the same thing. In desperation I clicked on the top left of the screen which showed a sort of dash and a dot that I'd never seen before. Doing this then revealed the 'apps' with which to use the system - not a menu in sight! (Now, perhaps I should have read the documentation, or been a little more inquisitive, but I genuinely thought there was a problem). What a crazy decision to minimize everything on a new installation, where there is a high chance that the user, like I was, is new to the UI. It seems to be a triumph of aesthetics perhaps over common-sense and what a poor introduction to the UI (Gnome)! After several hours of playing around, I really hated it anyway and installed the KDE UI, which I had been using with Linux Mint. I did so, but couldn't fully get rid of Gnome, so decided to start again and to install Fedora KDE Plasma Desktop instead!

At this point, I discovered the fun was only just beginning! The main problems I encountered with this new OS:

• Whilst I'd been able to write the Fedora Workstation iso file to the USB key OK from Linux Mint and boot from that without too much difficulty, trying to do so for the new OS on Fedora Media Writer was a problem -  I just couldn't boot from the USB key at all. It seemed that Legacy (BIOS) booting was no good and I had to use UEFI instead.
• After that, it booted from UEFI, but then it couldn't see the internal disk on the laptop! So, after much digging around, I found out that I had to change SATA operations to AHCI from RAID in BIOS/UEFI.
• I took the option to overwrite the existing Fedora installation, but that failed, so I chose to write to the entire disk.
• Finally, having installed the OS, I then installed Chrome and encountered a weird error with it. The issue was that while I could log in to my Google account, I couldn't see my bookmarks. Searching the issue came up with lots of helpful advice about synching the bookmarks, but I just couldn't see an option to do that. After, much digging, I had to enter chrome://sync-internals into the browser, then enable something called Sync-The-Feature. I got some pop-up about security and after that, the synch options became available and I was able to finally see my bookmarks! A pure Chrome issue or a combination of Chrome and new OS, I wonder?

I had a career in IT and am a reasonably competent user. Even so, I estimate it took at least 8 hours for me to do the 'upgrade' to Fedora. The experience puts me in mind of the difficulties I used to encounter decades ago, when nothing was ever simple with PCs and you needed to be a real 'tecchy' to get things working. Since then a lot has changed and we should expect things to work with minimal fuss. Software - OSs, UIs and applications - should be lightweight, intuitive, robust and not require extensive problem-solving.

As to what happened, perhaps part of the problem is that there are too many flavours of Linux and UI out there and they have to work across a wide range of hardware. It's all very fragmented, as indeed was the Unix world before Linux. Maybe things would work better if there was less choice?

(Oh and by the way, simple copy-and-paste doesn't seem to work with the mouse on my new system!)

Finding longitude before the invention of the marine chronometer

In recent posts about estimating the size of Astronomical Unit, I've stated that this couldn't have been done accurately before the advent of the marine chronometer to establish longitude.

Not so - it was the problem of the accurate measurement of longitude at sea, to determine the location of a vessel, that the marine chronometer solved.

Long before that, the use of astronomical tables, specifically of Jupiter's moons, allowed longitude to be measured with sufficient accuracy on land.

The relevant posts have been corrected.

Old devices refusing to be repurposed

(Originally posted on the RetroMat site in May 25, but sits better here). 

Buoyed by the successful rescue of an old Android phone (see below), I've just tried some other old devices that were lying in my electronic junk box, but unfortunately, for different reasons, I was unsuccessful:

•  Another Moto smart phone, different model, that simply fails to power on when connected to a power supply. Plug and phone get vaguely warm and when disconnected, there's a brief flash from the light at the front. Cause: battery failure.
•  An HTC Desire phone from around 2010. It starts promisingly: the battery gets charged, the phone powers up and displays a logo and vibrates and buzzes loudly, but the screen goes blank after a while. Sometimes it comes back on and the buzzing is repeated insistently, but it won't  go beyond that initial screen. Suspecting the removable battery could be at fault, I've checked it with a multimeter, but the voltage was pretty close to the specified value. I've been able to get to the Android menu by pressing and holding volume down and then the power button. I've then tried a few of the options there, such as erasing data, selecting the 'rescue' (reset?) option and even 'fastboot', whatever that is, but all to no avail. Back it goes into that box! Cause: hardware failure of some type.
• A Hipstreet W7 tablet. IIRC, this came free with a phone contract many years ago. No-one found it remotely useful at the time, so it was consigned to the box of unwanted devices soon after. Perhaps it could find some use at last as a media player? When plugged in, after some time, it starts up and displays a family member's name and a password prompt. There's a reset button, but all that does is restart the tablet, not reset it to factory settings. It seems, in order to rescue the device, it needs to be booted up with a previously-created rescue 'disc' in the usb port. Needless to say, there isn't one. Unfortunately, but not unsurprisingly, said family member doesn't recall the password after all this time. Cause: security policy.
• A 4 GB Sony Walkman (NWZ-A816) from around 2008. It was used often until I had my first smart phone a few years later. The battery had started to expand a while ago, so it was removed and disposed of at the recycling centre. It still powers up, though, if plugged into a power supply by USB cable. It can even be made to continue to function as a media player (music, photos, videos).  What it steadfastly refuses to do, however, is to reliably accept files that I try to transfer to it from my laptop - I keep getting message libmtp error: could not send object. IIRC, I had a similar message when trying to send files directly to the Moto G rather than to a MicroSD card mounted locally on my laptop. It's quite possible that the problem arises from the file transfer protocol as implemented in my laptop's OS (Linux Mint). However, given the limited usefulness of the device (small capacity, no battery, no support for flac files!), it's probably not worth pursuing further. Cause: incompatible standards?

Repurposing an old Android phone

(Originally posted on the RetroMat site in May 25, but sits better here).

For some time, I've been looking for a way to play my digital media through my Onkyo 'hifi' receiver from 2006 which has no USB port or SD card slot. I like the machine - it sounds great, is solidly-built and as well as a  CD player, has a radio, including MW, which I use for receiving distant stations. We have a Chromecast Audio that can be connected to it for on-line audio streaming. In all other respects, it meets requirements and I'm in no rush to replace it.

(I tried using an old QNAP NAS system, but it was a faff. IIRC, I was able to use it from our TV, using twonky, a now defunct standard, but would have had to move the receiver to the TV in order to connect the two and that wasn't convenient. Plus the TV won't play flac files. I think I tried using the NAS from my phone and casting from there, but couldn't find a way to stream from the NAS and instead had to download files. After that, I just gave up).

Years ago, when I had an Android phone with external storage, I'd connect the phone directly to one of the inputs. Since then, I've had hand-me-down iPhones and can't do that and my digital media has been restricted to my laptop.

There are impressive looking machines from Brennan. In time, I'd like to rip (losslessly) my entire CD collection, so one of these could make sense. However, they are bulky and somewhat over-specced for my needs: first I already have a CD player in the Onkyo, second I can rip CDs on a PC, and third, I don't really require all the high-tech connectivity they provide.

I could use a modern mp3-type player, but don't want or need a high-end device from the likes of Astell & Kern, or FiiO. Sony Walkman's are within my budget, but you have to pay up considerably if you want a decent amount of (non-expandable) internal storage. Plus, as with smart phones, such devices seem to be intended to be disposable, having batteries that may not be easy to replace.

For now, I've decided to re-use an old Android Moto smart phone with a MicroSD slot, with support for up to 512 GB of storage. I wasn't overly-optimistic at first that this would work after so many years. In fact, two other candidate phones couldn't be started. However, as I began to charge this one, it started OK and the battery seems OK. I've removed or disabled as many apps as I can, disabled wi-fi and bluetooth and as there's no  sensitive information any more, I've removed the screen lock, leaving what is in effect just an mp3 player. The google search prompt won't budge, but it's not a big deal. For now, it has just a 4 GB card in it and it's being used to play a mix of mp3, wav and flac format files. I'm planning to replace the card with a much larger one - how well it scales up in practice, we shall see.